POWER-TYPE STRENGTH TRAINING IN MIDDLE-AGED MEN AND WOMEN*
dissertation presented on the 11th February 2005 at the Auditorium
of The Petrea Rehabilitation Centre, Peltolantie 3, Turku, Finland
by permission of Faculty of Medicine of the University of Kuopio,
Department of Physiology, University of Kuopio, Department of Physiology,
Finnish Institute of Occupational Health, Kuopio, Finland
© Journal of Sports Science
and Medicine (2005) 4, Suppl.9, 1 - 36
Google Scholar for Citing Articles
review is based on the following original publications, which will be referred
to in the text as Studies 1-5:
Surakka, J., Alanen, E., Aunola, S., Karppi, S-L. and Pekkarinen, H. (2005)
Effects of external light loading in power-type strength training on muscle
power of the lower extremities in middle-aged subjects. International
Journal of Sports Medicine (in press).
2. Surakka, J., Alanen, E., Aunola, S. and Karppi, S.L. (2001)
Isoresistive dynamometer measurement of trunk muscle velocity at different
angular phases of flexion and extension. Clinical Physiology 21,
3. Surakka, J., Aunola, S., Alanen, E., Karppi, S.L. and Mäentaka,
K. (2004) Effect of training frequency on lumbar extension and flexion
velocity. Research in Sports Medicine 12, 95-113.
4. Surakka, J., Aunola, S., Nordblad, S., Karppi, S.L. and Alanen,
E. (2003) Feasibility of power-type strength training for middle-aged
men and women: self perception, musculoskeletal symptoms, and injury rates.
British Journal of Sports Medicine 37, 131-136.
Surakka, J., Alanen, E., Aunola, S., Karppi, S.L. and Lehto, P. (2004)
Adherence to a power-type strength training programme in sedentary, middle-
aged men and women. Advances in Physiotherapy 6, 99-109
strength declines with increasing age, and the power-type strength
characteristics decline even more drastically than the maximal muscle
strength. Therefore, it is important to design training programmes
specifically for sedentary middle-aged people to effectively improve
the power-type strength in leg and trunk muscles. To be suitable
for the target group, the exercise programmes should be feasible,
motivating and easy to practice. The aim of this study was to design
and investigate the effects and feasibility of a power-type strength
training programme in 226 middle-aged men and women, with 26 persons
as non-training controls. The subjects trained three times a week
during 22 weeks, in 12 groups with exercise classes of 10-20 subjects,
and using no or very little external equipment. All training sessions
were controlled and supervised by an professional instructor. Vertical
squat jump, standing long jump, 20 metre running time, maximal anaerobic
cycling power, maximal oxygen uptake, and angular trunk muscle flexion
and extension velocities were measured before and after the training
period to evaluate the training effects. Questionnaires concerning
employment, physical activity, smoking, musculoskeletal symptoms
and exercise motives were also filled in before and after the training
period. The greatest improvements were achieved in vertical squat
jump (18%) and in angular trunk flexion (14%) and extension (16%)
velocities. An external loading totalling 2.2 kg (attached) in ankles
increased the height in vertical squat jump by 23% and maximal anaerobic
cycling power by 12%, these improvements were significant compared
with subjects in no load training group (p = 0.03 in vertical squat
jump and p = 0.05 in maximal anaerobic cycling power). Exercise
induced injuries occurred in 19% of men and 6% of women. Low back
symptoms decreased in exercisers by 12% and knee symptoms (increased)
by 4% during the intervention. Of all subjects, 24% dropped out
during the training period. In summary, improvements were achieved
in several physiological performances reflecting the power-type
strength qualities, especially in vertical squat jump and trunk
muscle flexion and extension velocities. Improved perceived health
and fitness among the participants who completed the training programme,
and the relatively low number of injuries also indicate the feasibility
of the programme. The training programme is simple, and it also
seems to be practical among middle-aged, sedentary subjects. It
may be useful in preventing the decline of power-type strength characteristics
in middle-aged subjects.
WORDS: Adherence, feasibility, middle-aged, power-type strength,
training effects, training programme.
power, which is the product of the velocity and force of muscle
contraction, is needed for performing daily habitual tasks and activities.
Muscle strength declines with advancing age, starting at the beginning
of the sixth decade, and the power-type strength, i.e. the capacity
to produce explosive muscle force, declines more drastically than
the maximal muscle strength (Izquierdo et al., 1999;
Anton et al., 2004).
Mechanisms contributing to this development may include the loss
of Type II fast-twitch motor units (Lexell et al., 1988),
or intrinsic changes in muscle force and power production capacity
(Frontera et al., 2000).
The age-related strength decrease has been previously reported to
be faster in lower extremities than in the upper body (Asmunssen
and Heeboll-Nielsen, 1962;
Bemben et al., 1991).
Recently, Anton et al. (2004)
demonstrated similar age-related declines both in the arm and leg
Strength and power-type strength training are recommended for middle-aged
and even elderly people for the purpose of maintaining the functional
capacity (Häkkinen et al., 1998;
Izquierdo et al., 1999;
Jozsi et al., 1999).
This is important especially with increasing age, in connection
with daily activities and even in prevention of falling (Bassey
et al., 1992;
Skelton et al., 2002).
People are commonly engaged in and familiar with endurance training
and resistance training. In natural human movements, however, several
physiological functions interact simultaneously, and therefore,
all the components of muscular performance should be trained equally.
It has been suggested (Häkkinen et al., 1998)
that strength training in combination with some explosive types
of exercises be recommended as a part of overall physical training
to maintain the functional capacity in middle-aged and elderly people.
For explosive muscle performance, the underlying factors are muscle
fibre type, muscle hypertrophy and enzymatic and neural adaptations.
It is also important to investigate the impact of power-type strength
training on the low back and knee muscles and joints, as well as
the injury risks and adherence and motivation to training. For being
effective in improving the explosive muscle performance, training
programmes should be designed so as to be motivating, easy to achieve,
effective concerning the time spent in exercises, low in expenses,
and they should give consideration to the exercise history and present
exercise activity, health status and musculoskeletal symptoms and
diseases of the individual. Even the socio-economic status and the
social and economic environment should be taken into account when
evaluating the actual possibilities for completing the planned programme.
The exercises should be integrated in everyday life and take place
on a regular basis.
Both in physical training and in the rehabilitation of middle-aged
people, the endurance type training is commonly used, e.g. walking,
jogging, cycling or swimming. The effects of endurance exercises
are well known, and various training modes are established and widely
adopted by non- athletic people. However, in everyday life the explosive
muscle qualities are also needed in various tasks and reactions,
e.g. prevention of falls. Training that affects the explosive muscle
qualities should therefore not be ignored, especially when it is
known that explosive type strength declines with ageing more drastically
than maximal muscle strength. However, physical training has been
shown to be effective in preventing the decline of muscle power
provided that the intensity, duration and frequency of training
For decades, resistance training has been used for the purpose of
achieving strength and power, but this type of training needs special
training facilities and equipment. The purpose of this study was
to find out an alternative method for exercising the explosive muscle
characteristics that would use no or very little equipment, be simple
and effective, and feasible for middle-aged sedentary people. The
programme should also motivate the participant to continued physical
activity after the intervention.
OF THE LITERATURE
strength in leg and trunk muscles
Muscle actions are either isometric or dynamic. In isometric actions
the muscle length does not change, while dynamic contractions affect
the length. Dynamic muscle contractions can further be classified
into concentric and eccentric. In concentric contraction the muscle
length decreases and in eccentric contraction it increases. Human
movement is seldom based on purely isometric, concentric or eccentric
muscle contraction. Body segments are periodically organised to
impact forces, for instance, in running or jumping, where external
forces lengthen the muscle. In these phases, muscles act eccentrically,
and the concentric action follows for achieving positive work (Cavagna
et al., 1968).
A combination of eccentric and concentric muscle actions constitutes
what is called stretch shortening cycle (Komi, 1984;
Cavanagh, 1988). The eccentric
action influences the subsequent concentric phase so that the final
contraction is more powerful than a concentric action alone would
have been (Komi, 1984).
Strength is defined as the maximal amount of force a muscle can
generate in a specified movement at a specified movement velocity.
The power of muscle contraction is a measure of the total amount
of work that a muscle can produce in a given time period. This is
determined by the strength of the muscle contraction, by the distance
of contraction and the number of contractions in a time period.
A performance of daily activities requires both strength and power-type
strength, and therefore, muscle conditioning and strength training
should be supplemented by exercises with higher velocities. Typical
performances requiring explosive power-type strength include various
jumps, where the maximal strength level must exceed the load to
be moved (i.e. own body). The power-type strength is needed also
in high-velocity training requiring acceleration, fast running,
and rapid changes of direction (e.g. football, tennis).
Trunk muscles protect the spinal structures against potentially
harmful loads and sudden movements (Floyd and Silver, 1955;
The measurements of trunk muscle velocity, acceleration and torque
are important for investigating the stress components of the spine
(Beimborn and Morrissey, 1988).
Muscle biopsies from diskectomy patients have revealed selective
atrophy of fast-twitch fibres in low back muscles (Mattila et al.,
Zhu et al., 1989),
with physical inactivity presented as one of the possible explanations.
Poor trunk muscle function is a potential risk factor for low back
disorders (Suzuki and Endo, 1983;
Lee et al., 1995).
Measurements in power-type strength training studies
Force production and velocity of the neuromuscular system are the
major elements of power-type strength. Vertical jump tests are widely
used to evaluate the power-type strength of lower extremities. Measurement
of the vertical jumping height is a simple and reliable (reproducibility
r = 0.92) method for measuring the explosive force of leg muscles
(Bosco et al., 1982;
Bosco et al., 1983).
The height of vertical jump correlates with 60 m sprint running
(Bosco et al., 1983),
and also with the maximal power of Wingate cycling test (Maud and
Margaria's (Margaria et al., 1966)
staircase running test is another simple and reliable test of anaerobic
power. Standing long jump has also been widely used in sports research
in measuring horizontal explosive force of leg muscles (Bosco et
Vandewalle et al., 1987;
Manning et al., 1988;
Moir et al., 2004).
Twenty-metre sprint running is recommended as one of the methods
to measure maximal anaerobic performance (Rusko and Nummela, 1996;
Moir et al., 2004).
Rusko et al. (1993), Rusko and Nummela (1996),
and Nummela (1996)
developed a method that allows the evaluation of several determinants
of maximal anaerobic performance, including the changes in the force
of leg muscles and relative to speed in sprint running. Isokinetic
knee dynamometers have also been used to test the power of lower
extremities (Moffroid et al., 1969;
Osternig et al., 1977;
Several studies (Parnianpour et al., 1989;
Rytökoski et al., 1994;
Hutten and Hermens, 1997)
have shown the isoresistive dynamometer measurement of trunk muscle
flexion and extension strength and velocity to be reliable and valid.
Perceived health and fitness were assessed by using a five-point
Likert scale (poor, fairly poor, average, fairly good, good) that
has previously been used by, i.e., Moum, 1992
and Wolinsky and Johnson, 1992.
This method has shown to be reliable and consistent with the assessed
medical health and its functional consequences (Lundberg and Manderbacka,
Musculoskeletal disorders were inquired about by using the standardised
Nordic musculoskeletal questionnaire, which has shown to be a reliable
and valid method for that purpose (Kuorinka et al., 1987).
Effects of power-type strength training on leg muscles
Proteins are the major component constituting the contractile apparatus
of the muscle. There is a continuous process of protein synthesis
and degradation in the body (although the structure of the body
is stable). The half-life of proteins determines the rate of adaptation
to physical exercise training. The range of variation of the half-life
of proteins is from less than one hour to several weeks (Maughan
et al., 1997).
The contraction velocity of a muscle fibre is determined by the
isoform pattern of the contractile proteins. The muscle proteins
(i.e myosin heavy chains) Type I, Type IIa and Type IIb are the
prime determinants of the muscle contraction velocity. Type I represents
the slow and fatigue-resistant muscle contractions, while Type IIa
represents the fast, oxidative and fatigue-resistant muscle contractions
and Type IIb the fast, fatigable muscle contractions (Staron, 1997).
Upon initiation of training, changes in the types of muscle proteins
begin to take effect within a couple of training sessions (Staron
et al., 1994).
Heavy-resistance training promotes hypertrophy in all three fibre
types (I, IIa and IIb). The greatest growth is usually seen in Type
IIa, followed by Type IIb, and the least growth in Type I fibres.
Training with high velocity and at low loads does not lead to hypertrophic
changes in fibres. Transitions appear to occur within the Type II
subtypes, but there is no convincing evidence of transitions between
Types I and II (Deschenes and Kraemer, 2002).
Muscle training is the main contributor to strength and power gains
(Coyle et al., 1981;
Behm and Sale, 1993).
The influence of training is reflected both in neural adaptation
and muscle fibre composition (Komi, 1973;
Komi et al., 1978;
Moritani and DeVries, 1979;
Ross et al. (2001)
also speculated in their review that the nerve conduction velocity
might reflect the adaptation of nerve structure, with increased
diameter of axon and myelination. This adaptation may decrease the
refractory period of the nerve, which possibly allows increased
impulse frequency and potentially increased muscle activation. A
major part of the improvements in untrained subjects during the
initial weeks in power-type strength training is probably due adaptations
of the neural system, such as increased motor unit firing frequency,
improved motor unit synchronization, increased motor unit excitability,
and increase in efferent motor drive. Also, a reduction of the antagonist
and improved co-activation of the synergist muscles may explain
part of the changes (Häkkinen, 1994).
In a study of Aagaard et al. (2002),
the major part of the training induced improvements after 14 weeks
of resistance training were explained by increases in efferent neural
Power-type strength performance can be improved almost by means
of any training method, provided that the training frequency and
loading intensity exceed the normal activation of the muscle (Kaneko
et al., 1983;
Moritani et al., 1987,
Häkkinen and Häkkinen, 1995;
Häkkinen et al., 1998;
Izquierdo et al., 1999;
Jozsi et al., 1999;
Häkkinen et al., 2000;
Marx et al., 2001).
In investigating the strength and muscle power output in upper and
lower extremities in athletes engaged in various sports, Izquierdo
et al. (2002)
found that the maximal power output was produced at higher load
condition in lower extremities (45-60% of 1 repetition maximum)
than in upper extremities (30-45%). They suggested that the sports-related
differences might be explained, in addition to training background,
by differences in muscle cross-sectional area, fibre type distribution,
and by the different muscle mechanisms of the upper and lower extremities.
Kawamori and Haff discussed this finding in their review (2004)
and suggested that another possible explanation for the differences
may be the fact that during lower extremity exercises a larger part
of body mass must be lifted up, compared with the upper extremity
exercises. Several studies have shown enhancements in middle-aged
and in older subjects in maximal and fast force production (Häkkinen
and Häkkinen, 1995;
Häkkinen et al., 1998;
Izquierdo et al., 2001),
in explosive jumping performances (Häkkinen et al., 1998;
Häkkinen et al., 2000),
and isotonic muscle power output in lower extremities (Jozsi et
Cavagna et al. (1971)
were the first who showed that the elastic component of leg muscles
provides the additional power that is required for sustaining the
maximal velocity during sprint running. Furthermore, in studies
of Mero et al. (1981)
and Chelly and Denis (2001)
multi-jump performances correlated highly with sprint running in
young subjects. Consequently, Mero et al. (1981)
proposed the drop jump test to be useful in predicting maximal running
speed. Also, Young et al. (1995)
found a high correlation between concentric squat jump performance
and maximal running speed. Sprint running and initial acceleration
represent a complex movement where the stretch-shortening cycle
is dependent of the adaptation of the neuromuscular system and strength
(Mero et al., 1981;
Mero and Komi 1986,
Cronin et al., 2000).
Cronin et al. (2000)
found that for stretch-shortening cycle actions of short duration,
such in sprint acceleration, the greater maximal strength will lead
to greater instantaneous power production. The same authors pointed
out that in concentric actions which need high initial power production,
such as vertical squat jump, the neuromuscular ability to produce
the highest amount of power per time unit is more important than
maximal strength. Stone et al. (2003)
concluded that improved maximal strength was the primary component
in improving the jumping power. Explosive exercises (Linnamo et
and sprint training (Sleivert et al., 1995)
also seem to facilitate the neuromuscular system.
Three times a week of resistance training is generally recommended
for achieving enhancements in muscle strength and power in extremities
(Pollock et al., 1998;
Feigenbaum and Pollock, 1999).
Previous reports indicate that, to achieve training effects, the
minimum training frequency should be at least twice a week (Pate
et al., 1995;
DeMichele et al., 1997;
Feigenbaum and Pollock, 1999;
Kraemer et al., 2002).
Previous studies also show that detraining leads to a decrease in
strength and loss of training effect within a few weeks (Häkkinen
and Komi, 1983;
Narici et al., 1989;
Häkkinen et al., 2000).
One of the major exercise methods has been the use of heavy loads
to induce recruitment of high-threshold fast Type II motor units
by the size principle (Sale, 1988).
Another exercise method is to use light loads to maintain the specificity
of the exercise velocity and to maximise the mechanical power output.
Kaneko et al. (1983)
reported that 30% of maximal load resulted in the greatest improvement
in maximal mechanical power. There are several studies indicating
the specificity of power training (Komi et al., 1982;
Häkkinen and Komi, 1985;
Scutter et al., 1995).
Power-type strength training with lighter loads and higher shortening
velocities has been shown to increase the force output at higher
velocities, as well as the power development (Häkkinen and Komi,
Muscular power increased significantly when high training volume
and high-velocity exercises were used in training (Häkkinen and
Marx et al., 2001).
Previous reports support specificity of exercise type, i.e. the
greatest training effects are achieved when the same type of training
is used both in training and testing (Caiozzo et al., 1981;
Kanehisa and Miyashita, 1983;
Häkkinen and Komi, 1985;
Ewing et al., 1990;
Colliander and Tesch, 1990;
Morrissey et al., 1995).
Experimental studies examining the effects of power-type strength
training in middle-aged, sedentary men and women have usually compared
the pre and post training effects of resistance training. Most of
the intervention studies evaluating the effects of power-type strength
and resistance training are conducted with younger and physically
active subjects. Moreover, randomised, controlled studies in this
field are sparse. Especially few are training interventions evaluating
both the training effects and the feasibility aspects, including
injuries, adherence and motivation. A summary of previous studies
with power-type strength training programmes in the training protocol
is presented in Table 1.
of power-type strength training on trunk muscles
Despite the large number of different exercise protocols for trunk
muscles, scientific research investigating the specific effects
of power-type strength training on trunk muscle velocity in healthy
subjects is lacking. However, several studies concerning the exercise
effects in low back patients have shown that improved muscular fitness,
trunk muscle strength and power or spinal flexibility may prevent
future low back pain and spinal disorders (Biering-Sorensen, 1983;
Suzuki and Endo, 1983;
Mayer et al., 1985;
Lahad et al., 1994;
Harreby et al., 1997;
Abenheim et al., 2000).
Trunk muscles should be trained by various types of exercises (aerobic,
strength and power training) in order to provide many-sided and
sufficient loading for lumbar muscles. In a recent study of Pedersen
et al. (2004)
the authors showed that exercises which focused on reactions to
various expected and unexpected sudden trunk loadings together with
coordination exercises can improve the response to sudden trunk
loading in healthy subjects, without an increase in pre-activation
and associated trunk muscle stiffness. Lumbar exercises are recommended
in chronic and even in sub-acute low back pain, but not in acute
phase (Abenheim et al., 2000).
According to previous reports, it appears that a training frequency
of 1-2 times a week elicits optimal gains in strength and power
in trunk muscles (Graves et al., 1990;
Tucci et al., 1992;
DeMichele et al., 1997;
Pollock et al., 1998).
Previous studies (Graves et al., 1990;
Pollock et al., 1989;
Tucci et al., 1992)
have investigated the effects of training frequency on increased
strength of lumbar extension muscles, which, unlike the other muscle
groups, have a large potential for strength gains. Improved lumbar
extension strength can be maintained up to 12 weeks with a very
low training frequency (1 session per 2 or 4 weeks), when the volume,
type and intensity of training are constant (Tucci et al., 1992).
of power-type strength training in middle-aged subjects
Ageing leads to a loss in muscle mass, a decrease of strength and
a decline of contractile velocity (Aniansson et al., 1981;
Frontera et al., 1991).
The main reason for age-related decrease in strength is muscle fibre
atrophy (Lexell et al., 1988)
and the decreased contractile velocity may be related to a reduction
of the relative proportion of fast Type II muscle fibres (Lexell
et al., 1988;
Proctor et al., 1995).
This process accelerates in the beginning of the sixth decade both
in men and women (Lexell, 1988; Häkkinen, 1994).
In a study among men and women aged between 20 and 84 years, Akima
et al. (2001) estimated that the leg extension and flexion strength
declined by 8% on decade in women and by 12% in men. Metter et al.
(1997) reported that the decrease of muscle power is 10% faster
than decrease of strength in ageing men. Savinainen et al. (2004)
investigated the changes in physical capacity (hand-grip-, trunk
flexion and extension strength and aerobic capacity) during a 16
year follow-up period and found a greater decrease of physical capacity
in men (ranging from 11.6% to 33.7%) than in women (ranging from
3.3% to 26.7%).
Muscle strength and the ability of the leg muscles to produce force
rapidly are of importance, especially with increasing age, in connection
with daily activities, and even in prevention of falling (Bassey
et al., 1992; Skelton et al., 2002). Samson et al. (2000) found that the decline of leg muscle
strength and functional mobility accelerated in women from the age
of 55 years onwards; in men the decline was more gradual. In healthy
urban population of 35-, 45- and 55-year-old men and women, the
vertical jumping height was 25% greater in 35-year-old men than
in 55-year-old men, but the 35-year-old men were only 15% stronger
in trunk muscles than 55-year-old men (Viljanen et al., 1991; Era et al., 1992). The average vertical jumping height was at least as
good in physically active subjects as in those who were 10 years
younger but physically inactive (Kujala et al., 1994). In the same study, the authors observed that mixed training
with varied types of exercises for the neuromuscular system enhanced
the jumping height most. Korhonen et al. (2003) showed in their
recent study that the age-related deterioration in sprint running
in former sprint athletes was associated with reduced stride length
and increased ground contact time.
For the purpose of maintaining functional capacity, strength and
power-type strength training are recommended for middle-aged and
elderly people (Häkkinen et al., 1998; Izquierdo et al., 1999). In strength training the minimum of two sessions a week
is recommended for the adult healthy population (ACSM, 1998; Feigenbaum
and Pollock, 1999; Kraemer et al., 2002). Probably the same frequency is also needed for maintaining
and enhancing the power-type strength characteristics.
Previous studies on supervised resistance training programmes (Tsutsumi
et al., 1997), controlled circuit weight training programmes (Norvell
and Belles, 1993) and anaerobic training programmes (Norris et al., 1990) indicate that these training modes are beneficial both
for physical and psychological health. The perception of physical
ability and perceived fitness have improved in physical training
interventions in adults, independently of the type of activity (Caruso
and Gill, 1992; Bravo et al., 1996). Studies evaluating the effects of power-type strength
training programmes in middle-aged and older subjects are sparse
(see Table 1).
For being effective in enhancing explosive muscle performance, the
training programmes designed for middle-aged and older subjects
should take into consideration, in addition to age and gender, the
existing musculoskeletal symptoms, previous injuries, and exercise
history. A population survey (Uitenbroek, 1996) showed that exercise-related injuries constitute a high
proportion of all injuries, particularly in men. The amount of previous
injuries and exposure time may also increase the risk for injuries
(Van Mechelen et al., 1992; 1996). Poor physical condition increases the risk of
training induced injuries (Lysens et al., 1991) and highly intensive fitness programmes may even have
non-beneficial effects on physical health among less fit subjects
in the form of injuries, increased muscle pain, muscle soreness
and other training-related inconveniences (Egwu, 1996). When an injury occurs, athletic and well-trained subjects
suffer more of post-injury mood disturbances (caused by the loss
of active training time) than less trained people (Little, 1969;
Exercise programmes should to be safe enough for the exercisers
to avoid injuries and musculoskeletal consequences. This is especially
important in programmes designed for middle-aged, sedentary men
and women. Injuries and musculoskeletal symptoms also influence
the exercise motivation. Approximately 30% of adult population in
Finland (Helakorpi et al., 1998)
and the United States (Caspersen and Merrit, 1995) are sedentary.
Physical activity generally declines with age, with a temporary
increase in activity at the time of retirement (Bouchard et al.,
The decline is greatest when the activity is vigorous and unorganised,
and the decrease is greatest in men. Also, men are engaged more
often in vigorous physical activities than women (Caspersen et al.,
In Finland, physical activity declines in early adulthood and begins
to increase again at the age of 45-54 years (Helakorpi et al., 1998).
Physical activity can be promoted by various kinds of interventions.
In group-based exercise programmes the adherence has been highest
in interventions of short duration (Bij et al., 2002),
but the effects are usually temporary (Dishman and Buckworth, 1996).
In an aerobic exercise programme, the dropout rate was approximately
50% within six months (Robison and Rogers, 1994).
Adherence to physical activity is a complex interaction of personal,
behavioural and environmental conditions, including perceived health
and fitness, marital status, smoking, obesity, lack of time, previous
exercise behaviour, socio-economic status and neighbourhood (Grzywacz
and Marks, 2001;
Trost et al., 2002). The adherence is lower in high-intensity training, but
high training frequency is necessarily not associated with low adherence
(Perri et al., 2002). Future adherent behaviour in supervised training programmes
is positively influenced by previous physical activity, perceived
health and fitness, the spouse's support, agreements and training
facilities (Dishman et al., 1985).
THEORETICAL FRAMEWORK OF THE STUDY
strength and power-type strength decrease with increasing age and
also with inactivity. The decrease accelerates at the onset of the
sixth decade both in men and women. The loss of muscle strength is
observed in all muscles in the body, but the loss may be earlier and
greater in the proximal part of leg muscles compared with arm and
trunk muscles, probably caused by a lower use of leg muscles compared
with the arms and trunk. Maintaining strength and power-type strength
capacities at increasing age is relevant for a number of reasons,
including prevention of falls, maintenance of joint mobility, and
performance of daily activities.
Training intervention studies, and especially randomised studies,
investigating the effects of power-type strength training on leg and
trunk muscles, and further evaluating the feasibility of the programme
in question are sparse. The results of exercise interventions where
explosive exercises have been used in groups of sedentary, as well
as athletic middle-aged and older people are promising. However, most
of the studies have been conducted with a small number of participants,
and the exercise mode has in most studies been strength or resistance
training combined with explosive exercises, rather than explosive
exercises alone (Table 1).
As far as we know, there are very few studies on purely power-type
strength training programmes in middle-aged and older men and women.
The feasibility of this type of training programme, including such
aspects as training motivation, training adherence, training induced
injuries, musculoskeletal symptoms, and the impact of perceived health
and fitness, should also be investigated by using reliable and validated
AIMS OF THE STUDY AND STUDY DESIGN
Aims of the study
The general purpose of this study was to investigate the effects
of a power-type strength training programme on leg and trunk muscles,
and to examine the training responses in men and women with high,
moderate and low training activity. Additionally, the feasibility
of the power-type strength training programme for middle-aged, sedentary
men and women was evaluated. The following qualities were set for
the programme design: the programme should be simple and practical,
and it should encourage and motivate middle-aged men and women to
increase their overall physical activity by getting accustomed to
and adopting power-type strength training.
The individual studies were performed to specifically answer the
the use of light external loading (totalling 2.2 kg) in lower
extremities increase the efficiency in power-type strength training
exercises? (Study 1)
training frequency is needed for improved angular velocity of
the trunk muscles in power-type strength training in middle-aged
men and women? (Study 2 and 3)
is the influence of power-type strength training on perceived
health, musculoskeletal symptoms and injuries in middle-aged men
and women? (Study 4)
is the adherence rate in men and women, and what are the reasons
for dropping out from the power-type strength training programme?
hundred and fifty-two (252) subjects volunteered to the study. A
total of 171 participants completed the training programme, and
55 subjects dropped out during the training programme (Study 5).
The control group consisted of 26 non-exercising volunteers (Figure
For evaluating the impact of light loads attached to the lower extremities,
the exercisers were divided into two subgroups, one with light loads
and one without any loads. The results of those exercisers whose
training attendance was at least twice a week (high training group)
were included in the analysis (Study 1).
For evaluating the training frequency vs. training response, the
participants were classified into three training frequency groups
according to their attendance at the exercises, and to a non-exercising
control group. The subjects with training attendance rate > 67%
(2-3 times a week) were classified as female and male high training
groups; the subjects with training attendance rate between 33% and
67% (1-2 times a week) were classified as female and male moderate
training groups, and the subjects with attendance rate < 33%
(less than once a week) or with at least six weeks of detraining
period at the end of the intervention were classified as female
and male low training groups. The numbers of subjects participating
in different physiological measurements are presented by the training
attendance groups in Table 2.
For analysing the effects of training frequency on trunk muscles,
the participants were classified into two training frequency groups
(Study 3). The design of the study is presented in Figure
The physical performance measurements were performed and questionnaires
were answered one week before the training programme started, and
same procedure was carried out one week after the training programme
ended. The study was completed within two years: a new controlled
and supervised exercise class started once 10-20 subjects had been
measured, and the group continued training together for the whole
training period of 22 weeks. The training programme included three
progressive periods. The orientation period consisted of basic strength
and conditioning exercises (6 weeks). The second period consisted
of training for explosive strength and velocity (10 weeks), and
the last period consisted of velocity training (6 weeks).
To be eligible for the intervention, the participants should be
middle-aged, healthy and sedentary. All participants were examined
by a physician to be qualified to participate. Medical screening
included cardiovascular, neurological and musculoskeletal examinations.
The physical activity level was assessed by interviewing the subjects
(those who trained sports regularly, at least three times a week,
or had been training in the past five years were excluded from the
Participants (n = 252) were recruited among the staffs of the local
university and polytechnic institutes, secondary schools and private
companies, or among the participants of retraining courses and the
members of a local association of the unemployed. The recruiting
information was the same for all. Brochures about the training intervention
were attached on billboards providing the following information:
"The aim of this study is to develop in practice power-type
strength exercises that are simple to perform and feasible for anybody.
Exercise sessions are supervised, and various physiological measurements
are carried out before and after the intervention". The groups
were also reached by e-mail and by visiting people at their jobs,
course centres and institutes with the purpose of recruiting volunteers
to the intervention. The subjects in the training group (men n =
86, women n = 140) and in the non-exercising control group (men
n = 11, women n = 15) were healthy and middle-aged, and most of
the subjects were sedentary (Table
3 and Table 4). All subjects
were informed of the purpose of the study before they gave their
written consent to participate in the study. The Ethical Committee
of the Research and Development Centre of the Social Insurance Institution
approved the study protocol.
After the medical examination the following measurements were carried
out on four different days: Vertical squat jump, Trunk muscle performances
and all inquiries (Day 1); Maximal anaerobic cycling power (Day
2); Maximal oxygen uptake (Day 3); and Standing long jump and 20
metre running time (Day 4).
Vertical Squat Jump (Study 1)
Vertical Squat Jump (VSJ) (cm) was used to measure the explosive
force of leg muscles before and after the intervention. Participants
had three attempts in vertical squat jump, with 1-3 minutes' rest
between the attempts. The best value (cm) of the three trials was
included in the statistical analysis. VSJ was measured by using
a contact mat (Newtest powertimer®, Finland). The recorded flight
time (s) was transformed to centimetres (cm) (Bosco et al., 1982; 1983). Participants were barefoot, with knees flexed
at 100 degrees, and they held a wooden stick behind the neck to
standardise the position of arms and upper body.
20 metre Running Time (Study 1)
20 metre Running time (20mRT) (s) was measured with a flying start,
and the first 5 metres were omitted from the calculation of the
running time. Participants had three attempts in running speed,
with 1-3 minutes' rest between the attempts. The best result was
used in the statistical analysis.
Standing Long Jump (Study 4)
Standing Long Jump (SLJ) (cm) was used to measure the explosive
force of leg muscles in horizontal direction. Subjects jumped from
a standing position, swinging of arms and leg counter-movements
were permitted. Participants had three attempts. The best result
was used in the statistical analysis.
Maximal Anaerobic Cycling Power (Study 1)
The Maximal Anaerobic Cycling Power (MACP) (W) test is a cycle ergometer
modification of an anaerobic power test on a treadmill (Rusko et
al., 1993; Rusko and Nummela, 1996). MACP consisted of 3-8 cycling bouts lasting 20 s each
with a 100 s recovery between the bouts. The pedalling frequency
was constant, 90 rpm for men < 40 yrs and 86 rpm for women and
men > 40 yrs. The work rate of the initial bout was determined
by the subject's body weight and estimated physical fitness, supposing
that sedentary subjects were within the range of average maximal
oxygen uptake of population (or less). The load was increased by
30-60 W in general, depending on the subject's age, gender and physical
fitness. The work rate was increased after every recovery in equal
increments throughout the test. Cycling power, pedalling moment
and pedalling frequency were recorded and saved on a computer. A
cycling bout was accepted if the pedalling rate was not decreased
by 5% or more from the target speed. The subject continued the test
until he or she could not cycle at the target rate. The test ended
at the moment when the pedalling rate was decreased by 5%. To be
acceptable, the final bout was not to be shorter than 12 s. The
maximum of the moving average over the 5 s period of cycling power
was applied for describing the maximal anaerobic cycling power of
the subject. The cycle ergometer used in the test was RE 820 (Rodby
Elektroniks AB, Södertälje, Sweden), which was modified to give
power output of 1000 W with high pedalling rate.
Maximal oxygen uptake (Study 1)
Maximal oxygen uptake (VO2max) (ml·kg-1·min-1) was measured to evaluate
the subject's endurance capacity. A 2-min incremental exercise test
on the electromagnetically controlled cycle ergometer (Rodby Ergometer
RE 820®, Södertälje, Sweden) until volitional exhaustion or fatigue
of the lower limbs was employed for measuring the VO2max. The subjects
pedalled at a constant frequency of 60 rpm. The test was preceded
by a 4-min warm-up at 30 W to become familiar with the pedalling
frequency, mouthpiece and nose clips. Thereafter, work rate was
increased every 2nd min, with equal increments throughout the test.
The increments were individually determined (10-25 W) on the basis
of the subject's physical fitness to reach the maximum work rate
in approximately 12-15 min. The test continued until the subject
was unable to maintain pedalling frequency above 45 rpm. Respiratory
gas exchange variables were determined continuously with a breath-by-breath
method suing the SensorMedics Vmax 229® equipment. The VO2 values
were averaged over the breath-by-breath values of the 30-second
intervals. VO2max was recorded as the highest averaged value at
the maximum work rate. The corresponding heart rate and work rate
were recorded and represented their maximums. Subjects rated their
perceived exertion using the Borg scale 6-20 (Borg, 1982) and the amount of fatigue in their lower limbs on scale
1-5 every 4 minutes at the beginning and every 2 minutes later on
during the test and at the end of the test in order to evaluate
subjective feelings along the whole exercise test and the character
of subjective maximum.
Isometric and dynamic trunk Flexion and Extension torques and
angular velocities (Study 2, 3)
Isometric trunk flexion (IsomFL) (Nm) and extension (IsomEX) (Nm)
torques, and the trunk flexion (FLTorq) (Nm) and extension (EXTorq)
(Nm) torques during dynamic actions, and the angular velocities
during flexion (FLvel) (deg·s-1) and extension (EXvel)
(deg·s-1) were measured by using a triaxial, isoresistive
lumbar dynamometer (Isostation B-200®, Isotechnologies, Hillsborough,
NC, USA). The system allows simultaneous measurement of the velocity,
angular position and torque of the three spatial axes of the body
Questionnaires (Study 1, 4, 5)
Questionnaires were used to inquire about the physical activity,
smoking, employment status, motivation for exercising, and perceived
health, fitness and musculoskeletal disorders. The participants
filled in a questionnaire asking yes or no questions about the present
and previous physical activity (excluding school-time sports activities),
smoking (yes or no) and employment (yes or no).
Perceived health and fitness were assessed by using a five-point
Likert scale (poor, fairly poor, average, fairly good, good) used
by, among others, Moum (1992) and Wolinsky and Johnson (1992). This
method has shown to be reliable and consistent with the assessed
medical health and its functional consequences (Lundberg and Manderbacka,
1996; Manderbacka, 1998).
For the assessment of musculoskeletal disorders, the standardised
Nordic musculoskeletal questionnaire (Kuorinka et al., 1987) was used. The subjects were inquired about the presence
of neck, shoulder, low back, hip, knee and ankle symptoms during
the preceding six months. Further, the participants were in advance
instructed to report the instructor about any injuries occurring
during the training programme, and to describe the injuries in detail.
In order to minimise the number of missing reports, the participants
were given a questionnaire form for reporting the injuries. They
were also asked to evaluate whether the injury was acute or a result
The power-type strength training programme was based on the general
training principle with the exercises performed with low loads,
but with high movement velocities. The aim was to activate the muscles
subject to training by various exercises to a high or maximal degree,
with a short activation time. This type of training leads to improvements
primarily in the earlier force portion of the force-time curve or
the higher velocity portions of the force-velocity curve (Häkkinen,
Training sessions were supervised and controlled by a qualified
instructor. The duration of the training programme was 22 weeks,
including 52 training sessions, which lasted 60 minutes each. The
targeted exercise frequency was three times a week. The training
programme (described in detail in original Studies 1, 3 and 5) was
progressive, with an emphasis on power-type strength training. The
programme included the following three periods: the first period
of 6 weeks consisted of basic physical exercises, the second period
of 10 weeks consisted of power-type strength training and the third
period of 6 weeks consisted of power-type strength and velocity
training. The purpose of the first period was to familiarise the
exercisers with physical training and to enhance muscle strength
and co-ordination skills. The second period consisted of power-type
strength training with submaximal and maximal intensity. The third
period consisted of power-type strength and high-velocity training
with maximal intensity. During the first exercise week the intensity
of training was determined individually for each participant on
the basis of maximal Number of Repetitions subjects performed during
60 s (NR). The maximal Number of Repetitions during 60 seconds was
calculated for various types of exercises. The exercises focused
on leg (approximately 60%) and trunk muscles (approximately 40%).
Training was carried out in male and female exercise classes of
10-20 subjects. After the first 6 week period exercisers were divided
into Light Load (LL) or into No Load (NOL) groups. Exercisers in
the LL group had 1.1 kg weights in each ankle during all exercises.
Each exercise class consisted of either LL or NOL exercisers.
General Linear Models Procedure (GLM) of the Statistical Analysis
System (SAS/STAT, 1989) was applied to compare the changes between
the groups and to evaluate possible interaction between group and
gender, and for multiple comparisons between the groups. Mean changes
and lower and upper 0.95 confidence limits of the outcome variables
in three different training activity groups and the control group
were calculated by gender. Means, standard deviations and correlation
coefficients were calculated by standardised methods.
For the comparison of the changes in the Light Load (LL) and No
Load (NOL) groups (Study 1), the individual data for VSJ, 20mRT,
MACP and VO2max at the baseline and after the intervention were
presented in scatter-plots. The chi-square test was applied to examine
the distribution of the type of previous exercise activity (four
categories: endurance type, power-type, no exercise history, and
other leisure activity than endurance or power-type), and the pre-training
shoulder-neck, low back, hip, knee and ankle symptoms. The t-tests
were used to analyse the differences between the mean values of
the baseline measures and the changes in the LL and NOL groups.
The Linear Structural Relationships (LISREL) model was used to analyse
the flexion and extension movement velocities and the reliability
of the measurement (Study 2). The LISREL model facilitated understanding
the nature of the measured flexion and extension movement, movement
velocity and range.
For the analysis of the trunk muscle performances (Study 3), one-way
analysis of variance (Procedure GLM of the Statistical Analysis
System) was applied to compare the changes of the outcome measures
between two (high vs. low training) groups by gender. The chi-square
tests were applied to investigate the differences in low back symptoms,
perceived health, physical activity, and smoking between the groups.
Mean changes and lower and upper 0.95 confidence limits of the outcome
variables in three different training activity groups and the control
group were calculated by gender. Means, standard deviations and
correlation coefficients were calculated by standardised methods.
The chi-square test and the GLM procedure analysis were applied
to examine the distribution of the musculoskeletal symptoms, smoking,
employment, perceived health, perceived fitness, overall physical
activity (present and previous) and smoking between the groups.
To investigate whether there were any changes in perceived health,
in perceived fitness, or in the incidence of knee and low back symptoms
during the training programme, the marginal probabilities of two-dimensional
contingency tables were used and analysed by gender using Proc Catmod
SAS/STAT (Study 4). The chi-square tests and the GLM Procedure analysis
were applied to investigate the associations with training activity
and employment, smoking and age (Study 5).
Study subjects and training effects on leg muscle performances
in exercisers and non-training controls
One hundred and seventy-one (171) participants (64 men and 107 women)
completed the training programme. The control group consisted of
26 non-exercising volunteers (11 men and 15 women). Of the initial
group, 55 dropped out (22 men and 33 women) during the training
programme. The overall dropout rate in this study was 24%. The overall
training activity was 63% for those (n = 171) who completed the
programme. The baseline characteristics of the subjects are presented
in Table 3 and Table
4, including age, body mass index, perceived health and fitness,
jump performance, and knee and low back symptoms. At the baseline,
the exercisers (n = 171) did not differ from the non-exercising
controls (n = 18) or dropouts (n = 55).
In performances requiring power-type strength the most visible training
effects were observed in vertical squat jump with 18% improvement
in exercisers (15% in men and 20% in women), while in controls the
increase was 1% (no change in men and 2% increase in women). Trunk
flexion velocity improved in exercisers by 14% (13% in men and 15%
in women), whereas in controls the increase was 3% (5% in men and
1% in women). The improvement in extension velocity was 16% (15%
in men and 17% in women) in exercisers, while the increase in controls
was 5% (7% in men and 3% in women). The exercisers improved their
results in standing long jump by 4% (1% decrease in controls), 20
metre running time by 5% (no change in controls) and maximal anaerobic
cycling power by 6% (1% increase in controls). In maximal oxygen
uptake, which was measured for individual endurance capacity, a
4% improvement was observed in exercisers (2% decrease in controls).
The changes in the non-training control group were not significant
in any of the measurements. The pre- and post-intervention values
and the percentage changes of the vertical squat jump (cm), standing
long jump (cm), 20 metre running time (s) and maximal anaerobic
cycling power (W) for the different training activity groups in
men and women are presented in Table
5 and Table 6.
There were significant differences in changes between the groups
in vertical squat jump (F = 19.33, df = 3, p = 0.0001), in standing
long jump (F = 4.20, df = 3, p = 0.007), in maximal oxygen uptake
(F = 3.10, df = 3, p = 0.03), in 20 metre running time (F = 11.35,
df = 3, p = 0.0001), and in maximal anaerobic cycling power(F =
4.83, df = 3, p = 0.0003). In vertical squat jump the changes were
higher in all of the training groups compared with the controls
(p < 0.05). In 20 metre running time, the changes were greater
in the high and moderate training groups compared with the controls
(p < 0.05). In standing long jump, in maximal anaerobic cycling
power and in maximal oxygen uptake the changes were greater in the
high training group compared with the controls (p < 0.05). In
maximal anaerobic cycling power the changes were greater in the
high training group compared with the low training group (p <
Mean changes and 0.95 confidence limits in vertical squat jump (Figure
2a), 20 metre running time (Figure
2b), standing long jump (Figure
2c), maximal anaerobic cycling power (Figure
2d), and maximal oxygen uptake (Figure
2e) are shown for the three training activity and control groups
and by gender.
No significant gender differences were observed in the changes of
vertical squat jump, standing long jump or in the maximal oxygen
uptake after the training programme. Women achieved greater changes
after the training in 20 metre running time (F = 10.62, df = 1,
p = 0.01), while men achieved greater changes after the training
in maximal anaerobic cycling test (F = 5.86, df = 1, p = 0.02).
Effects of external light load vs. no load on muscle power in
lower extremities (Study 1)
No significant differences were found between the light load and
no load groups concerning the type of previous exercise activity,
perceived health and fitness, and shoulder-neck, low back, hip,
knee and ankle symptoms at the baseline (Study 1), or immediately
after the intervention. No significant differences between the groups
were observed in body weight after the intervention. There were
no differences in exercise induced injuries between the light load
and no load groups. At baseline, no differences between the groups
were observed in vertical squat jump, 20 metre running time, maximal
anaerobic cycling power or in maximal oxygen uptake values (Study
1). After the intervention, subjects in the light load group (with
2.2 kg external loading in ankles) improved vertical squat jump
by 23% (p = 0.03) and maximal anaerobic cycling test by 12% (p =
0.05). The changes are significant compared with the no load group
(16% increase in vertical squat jump and 5% increase in maximal
anaerobic cycling power) (Study 1). No differences were observed
in 20 metre running time between the light load and no load groups.
Measurement of trunk flexion and extension velocities (Study
The analysis of the repetitive trunk muscle flexion and extension
velocities at three angular phases showed that the peak velocities
of the second phases of these movements (between 15° and 35° in
flexion and between 20° and 0° in extension) correlated highly (r
= 0.99) with the peak velocity of the whole movement (from -5° to
55° in flexion and from 40° to 20° in extension) both in flexion
and extension. Correlations were high both before and after the
22-week intervention. The LISREL analysis showed high reliability
in peak flexion (r = 0.78) and extension (r = 0.81) velocities between
the pre- and post-intervention values (Study 2).
of power-type strength training on trunk muscle performances (Study
The age, weight and height or lumbar spine measurements at baseline
of women and men did not differ between the groups (Study 3), and
no difference between the groups were found in self-reported low
back symptoms, perceived health and fitness, physical activity and
smoking at baseline (Study 3).
Differences were observed in training induced changes of peak flexion
velocity between the female and male high training groups vs. female
(F = 7.54, p = 0.008) and male (F = 4.86, p = 0.03) low training
groups, and in peak extension velocity correspondingly (F = 9.07,
p = 0.003 for women, and F = 12.31, p = 0.001 for men). The training
induced change in peak flexion velocity was 13 deg/s greater both
in the female and male high training groups than in the corresponding
low training groups (p < 0.05). The change in peak extension
velocity was 15 deg·s-1 higher in the female high training
group than in the female low training group (p < 0.05), and 18
deg·s-1 higher in the male high training group than in
the male low training group (p < 0.05).
Effects of training on perceived health and fitness (Study 4)
Both male and female exercisers perceived that their physical fitness
improved (p < 0.01 for men and p < 0.0001 for women) during
the intervention period. Perceived physical health improved in female
exercisers only (p < 0.001).
The male dropouts showed a significantly poorer perceived health
than the exercising men (p < 0.01). Men attended 62 ± 23% (mean
± SD) and women 66 ± 18% of the scheduled training sessions. Twelve
men and 25 women attended 80% or more of the scheduled training
sessions. Those with a training attendance > 50% showed
improved perceived fitness; in women the change was significant
(p < 0.05). While significant improvements occurred in perceived
physical fitness (men and women) and in perceived physical health
(women), the control subjects (n = 18) did not show any changes
in either of these variables.
Men with improved vertical squat jump performance showed improved
perceived health (p < 0.05) and women with improved standing
long jump performance showed increased perceived fitness (p <
0.05). No such trends were observed in the controls.
and low back symptoms, and training induced injuries during the
intervention (Study 4)
exercisers the number of men reporting no low back or knee symptoms
increased from 20 at the baseline to 25 after the intervention,
and in women the corresponding values were 49 and 55. The frequency
of low back symptoms decreased by 13% (p = 0.06) in men and by 10%
(p = 0.06) in women. Knee symptoms increased by 2% (p = 0.8) in
men and by 5% (p = 0.35) in women. Among the controls, low back
symptoms decreased by 11% and knee symptoms increased by 6%. Exercising
men who reported more knee symptoms after the intervention had higher
body mass index (28 ± 3, p < 0.05) than men on average (26 ±
3). The same was not observed in women. Of those participants who
had no knee symptoms before the intervention, 17% reported symptoms
in their knees during the programme, and 14% of the participants
who had knee symptoms before the intervention reported after the
programme that their symptoms had relieved.
The injury rate during training sessions was on average 10% (n =
16); 19% for men (n = 10) and 6% (n = 6) for women. The injuries
included non-specific knee pain (19%), sprain or strain in thigh
(37%) and calf muscles (13%), twisted ankle (19%), muscle cramp
in low back (6%) and strained shoulder muscles (6%). Five participants
sustained overuse injuries during the intervention, including non-specific
knee pain (n = 2), low back pain (n = 2) and pain in calf muscle
(n = 1).
to training programme (Study 5)
analysis of the data concerning all the participants (n = 226) who
started to exercise showed that the training activity was associated
with unemployment (F = 15.2, p < 0.0001), smoking (F = 5.21,
p = 0.02) and age (F = 3.88, p = 0.05) with the younger subjects
having lower adherence to the programme. No association was observed
between training activity and gender, body mass index, shoulder,
neck, low back, knee or ankle symptoms, perceived health or fitness.
Twenty-two of the dropouts interrupted because of lack of motivation,
18 because of lack of time, 8 because of an exercise induced musculoskeletal
symptom, and 7 because of other reasons.
The subjects' age and body mass index, the distribution of smoking,
previous and present physical exercise activity, the rate of physical
leisure activity, perceived health, perceived fitness and musculoskeletal
symptoms are presented in Table
2 for men and in Table 3
Of all female smokers 57% dropped out of the training programme,
while only 15% of female non-smokers dropped out (p < 0.05).
Of all female participants the unemployed women smoked significantly
more (p < 0.01); this was not observed in men.
Among the subjects in age groups < 40 years, 40-49 years and
> 50 years who completed the training programme, the significantly
lowest training attendance (%) was found in women under 40 years
of age (58 ± 19%) (p < 0.05). The attendance rate was 66 ± 19%
in women > 50 years and 69 ± 16% in women aged 40-49 years.
The overall unemployment rate was 21%. The unemployment rate was
47% among the dropouts, while it was 8% in high training, 16% in
moderate training and 17% in low training groups. Nineteen (19)
percent of dropouts perceived their fitness good, whereas 48% of
exercisers had good perceived fitness (p = 0.02). Most of the subjects
trained both for physical and mental well-being (approximately 43%),
the second frequent motive for physical training was mental well-being
Training effects on leg muscle performances
The power-type strength training programme was effective in
improving the middle-aged participants' physical performances
requiring explosive muscle force, expressed here by the vertical
squat jump, 20 metre running time, standing long jump, and
their maximal anaerobic cycling power. The changes are comparable
with previous studies (Kaneko et al., 1983; Wilson et al., 1993; Aagaard et al., 1994).
In a study of Häkkinen and Komi (1985),
the measured jumping height increased by 21% in well-trained
young men who trained progressively mainly jumping exercises
for 24 weeks. In a study of Judge et al. (2003)
in highly skilled athletes, the increase in rapid isometric
knee extension was 24% after a 16-week sport-specific resistance
training, and in a study of Delecluse et al. (2003)
in young untrained women, 12 weeks of moderate resistance
training (10-20 repetition maximum) increased the dynamic
knee extension strength by 7%, but the explosive strength
(measured by countermovement jump height) remained unchanged.
In the present study, the enhancements attributable to the
power-type strength training were similar in men and women,
except for 20 metre running time where no change was observed
in the male low training activity group. Women's results tended
to show higher improvements in vertical squat jump. Women
in training groups showed lower baseline values than the female
controls, and it is known that, when they start to exercise
regularly, less fit people achieve higher gains in comparison
with well-trained individuals measured by most of the indices
of physical fitness (Blair et al., 1996; Winters-Stone and Snow, 2003). This may be one of the explanations for the higher changes
in women in the present study.
Greater improvements would probably have been achieved in
standing long jump, if the training had resembled more the
test performance. In addition to this training specificity
effect, standing long jump demands flexibility, and also certain
performance technique. Perhaps greater attention should have
been paid to the flexibility training to reduce muscle stiffness
and increase the elasticity. It can be assumed that the middle-aged
and mostly sedentary participants to this study were initially
within the normal range or below the average in terms of flexibility,
and further, it can also be assumed that they had no practice
in the standing long jump technique, neither before nor during
the intervention programme. Ageing and sedentary lifestyle
leads to a decline in the function of the tendons and decreased
strength of the joints (Kannus and Jozsa, 1991; Vailas and Vailas, 1994; Tuite et al., 1997),
and consequently, flexibility exercises are important for
reducing the stiffness of the muscles (Wilson et al., 1991).
The electromyographic activity was not measured in this study,
but it is presumed that a great part of the enhancements,
especially in vertical squat jump but also in the other physiological
measurements, were due to the neuromuscular adaptation (Moritani
and DeVries, 1979;
Cronin et al. (2000)
also stressed the importance of the adaptation of the neuromuscular
system in concentric muscle actions that require higher rates
of initial power production, such as vertical squat jumps.
Impact of light loading on muscle power in lower extremities
One of the aims of the study was to investigate the impact
of light external loading on the training effect in leg muscles.
The results show that an external loading totalling 2.2 kg
in ankles improved the jumping height and maximal anaerobic
cycling power, but not the sprint running performance. If
the training programme had been carried out with heavier weights
and with individually determined progressions of loading,
greater improvements would probably have been achieved. For
over 20 years ago, Komi et al. (1982)
showed that power-type strength training without external
resistance leads only to minor increases in the size of fast-twitch
All the subjects in the light load group used the same total
loading of 2.2 kg during the 16 training weeks, independent
of gender or body weight. The progression in our study involved
increased velocity and greater effort in exercises by time
period. Except for the light external loads in the light load
group, the training programme was similar in contents for
both groups. Mazzetti et al. (2000)
compared the effects of heavy-resistance training between
supervised and unsupervised training groups. The improvements
were higher in the supervised group, in which the training
load and progression were increased and adjusted by the supervisor.
The rate of progression was probably the primary factor contributing
to higher physical improvements in the supervised group, compared
with the unsupervised group.
Driss and co-workers (2001)
found in their study that when external loads of 5 and 10
kg were used, the instantaneous peak power in squat jump decreased
in untrained subjects, but not in volleyball players and weight-lifters.
The authors suggested that vertical jump height was associated
with previous training activity, and similarly, in sprint
running the running technique may also be related to previous
The use of light loads in the present study had an impact
on jumping height, but not on the 20-metre sprint performance.
In a study by McBride et al. (2002),
the men who exercised with loads corresponding to 30% of their
repetition maximum increased their jumping height significantly
more than the men who trained with loads corresponding to
80% of repetition maximum. The loads were heavier than in
the present study, but the trend is similar. However, in the
study of McBride et al. (2002)
there was no significant difference between the groups in
20 m sprint running time.
Cronin et al. (2000)
pointed out the importance of maximal strength in initial
power production in stretch-shortening cycle actions, but
according to the authors, the adaptation of the neuromuscular
system was even more important in concentric muscle actions
that require higher rates of initial power production, such
as vertical squat jumps. On the other hand, Stone et al. (2003)
found in their study that strength training with lighter loads
(between 10% - 40% of one repetition maximum) and squat jump
had high correlations (ranging from r = 0.84 to r = 0.90).
The authors concluded that strength training with loads from
10% to 40% of one repetition maximum is the primary component
in improved jumping height. This finding is supported by the
study of Moss et al. (1997),
in which they measured the elbow flexor strength, power and
angular velocity and found that performance velocity increases
at submaximal level when maximal strength increases.
Both strength training and high-velocity training are needed
for sprint running, and according to Delecluse (1997),
high-velocity training is particularly effective in enhancing
the acceleration phase at the beginning. In the present study,
5 metres only were omitted from the calculation of the 20
m sprint running performance. Therefore, it is highly probable
that part of the acceleration phase was actually included
in the measurement. The distance of 20 metres for sprint running
was chosen because the aim was to explore possible increase
of maximal leg muscle power. Including the end of the acceleration
phase in the measurement, this distance was supposed to be
a more sensitive measure than running a distance at maximal
running speed (in which case the distance should have been
at least 30 m). With a longer maximal running phase, the leg
muscle power might be concealed by a poor running technique
in sedentary subjects.
Sprint running perhaps needs more practice in elementary running
technique, and the use of loads is of minor relevance when
middle-aged, sedentary "beginners" are exercising.
When untrained subjects in a study of Mero and Komi (1985)
were towed to supramaximal running speed (above their normal
maximal speed), they were unable to increase the stride rate,
and instead, they responded to increased speed with inefficient
increase of stride length. Well-trained athletes succeeded
to increase both stride rate and stride length in the said
study. This difference in running techniques between untrained
and trained individuals indicates that with sprint exercise
(supramaximal exercises) it is possible to adapt human neuromuscular
performance to a higher level.
The explosive force production increased markedly in leg muscles,
as suggested by the significant changes in vertical squat
jump. The vertical squat jump performance demands only concentric
muscle work, and no stretch-shortening cycle occurs. The smaller
improvements in 20 metre running time in the previously untrained
participants may also be explained by the lack of elasticity,
as well as protective mechanisms in muscles and tendons in
trying to avoid injuries. In sprint running the effect of
elastic properties and the function of tendons is of greater
importance than in vertical squat jump. The role of protective
mechanism is supported by the finding of Schmidtbleicher and
that, in drop jump exercises from varied heights untrained
subjects responded with an inhibition (reduced agonist muscle
activity) during the stretch load phase (eccentric), while
trained subjects reacted with a facilitation (increased agonist
muscle activity). A reduction in the electromyographic activity
before the ground contact has been observed in untrained subjects,
and this is suggested to be a protective mechanism by the
Golgi tendon organ reflex, acting during sudden stretch loads
In the present study, all of the participants might have achieved
higher absolute results in performance tests with a more sufficient
warming-up before the tests. In a recent investigation of
Gourgoulis et al. (2003),
the vertical jump ability increased by over 2% after a proper
warming-up before the performance test, and the subjects with
high initial strength improved their jump ability by 4%. The
warming-up effect probably has similar effects in other performance
tests requiring explosive force as well.
of the trunk velocity measurement
The reliability of trunk muscle velocity measurement between
interventions was high. In the trunk flexion and extension
movements, the purpose was to achieve the highest velocities
possible. In order not to compromise the reliability of the
measurement, the resistance was set at 20% of the individual
maximal isometric torque. In previous studies, resistances
between 30% and 70% of isometric maximum have been used for
achieving good reproducibility (Parnianpour et al., 1989;
Rytökoski et al., 1994).
The angular phases from 15 to 35 degrees in flexion and from
20 to 0 degrees in extension represented the peak velocity
of the whole movement, and thus, a reliable peak value of
flexion and extension velocity can be achieved at a narrow
angular phase of 20 degrees. The LISREL analysis reflected
the way of performing the movement: the faster the start the
slower the end, and vice versa.
Training effects on trunk muscle performances
The training resulted in significant improvements in trunk
flexion (14%) and extension (16%) velocities in all exercisers.
The results indicate that the design and progression of the
programme were successful for the purpose of achieve improved
trunk muscle velocity in sedentary middle-aged subjects, in
spite of the fact that the training mainly focused on lower
extremity muscles (40% trunk exercises and 60% leg muscle
In the present study, the various training subfields (basic
strength training and co-ordination skills, strength training,
and power-type strength training) were not mixed with each
other during the same training period. Häkkinen et al. (1998)
found that a training programme that was composed of a mixture
of exercises increasing muscle mass, maximal force, and explosive
strength led to significant gains in maximal isometric force,
but not in velocity properties. The authors attributed this
to the mixture of three different performances, with too little
effort on developing the explosive strength.
After the training intervention, the subjects with a training
frequency of at least twice a week achieved significant improvements
in the peak velocity of the trunk flexion and extension, when
compared with subjects who trained once a week or less. This
is an important piece of information for establishing the
dose-response effect of power-type strength training. The
finding is in line with a previous study by DeMichele et al.
in which the relative improvement in torso rotation strength
was highest in the group that trained 2 times a week. In the
said study, the differences were not significant between the
groups training 2 times or 3 times a week, but the subjects
who trained 3 times a week complained more about minor muscle
soreness and fatigue than those who trained once or twice
a week. This may have influenced the higher improvements in
the results of the group that trained twice a week.
On the other hand, Graves et al. (1990)
suggested that as low a training frequency as once a week
was effective enough to improve isolated lumbar spine extension
strength, and Pollock et al. (1989)
demonstrated that lumbar extensor muscles have large potential
for strength improvements. Also, the strength and power are
usually 30% greater in trunk extension than flexion in most
conditions (Beimborn and Morrissey, 1988).
However, DeMichele et al. (1997)
and Graves et al. (1990)
applied the same apparatus and procedures both in training
and testing, whereas in the present study the movements in
actual training and during the measurement sessions differed
from each other. Several studies (Baker et al., 1994;
Morrissey et al., 1995;
Murphy et al., 1994;
Scutter et al., 1995;
Wilson et al., 1996;
Judge et al., 2003)
have shown a better transference of training gains to the
measurement situation when the movement velocity, resistance,
subject's position during performance, and type of muscle
contraction in trunk exercises are as similar as possible.
Trunk muscles should be trained by various types of exercises
(aerobic, strength and power-type strength training) in order
to provide many-sided and sufficient stimulus and loading
for trunk muscles. Therefore, for achieving this goal, power-type
strength training should also be included in the training
programs designed for the middle-aged and even elderly people.
Training frequency is an important factor in the prescription
of exercise for healthy subjects, who may benefit from power-type
strength training through a reduced risk of low back disorders
or low back pain.
of power-type strength training in middle-aged men and women
The injury rate in the present study was 19% in men and 6%
in women. The rates are relatively low, considering the training
mode, i.e. explosive exercises with maximal effort. Higher
injury frequencies have even been encountered in endurance
sports (Koplan et al., 1982;
Blair et al., 1987).
Any interruptions in training due to musculoskeletal symptoms
and injuries were short, suggesting that the disorders and
injuries were not serious. On the other hand, all training
sessions in the present study were controlled and supervised,
whereas endurance sports are usually practised individually
without guidance. The higher injury rate among men in the
present study was in line with a survey of exercise-related
injuries by Uitenbroek (1996).
Muscle strains occurred mainly during sprint or step-aerobic
exercising and twisted ankles during jump or sprint exercising,
whereas overuse symptoms and disorders in knees, leg muscles
and low back muscles were mostly caused by sprint or jumping
exercises. As mentioned before, the training programme was
supervised, which counterbalanced and perhaps prevented injuries,
in spite of the fact that the participants - middle-aged,
mostly sedentary men and women - are a risk group for injuries
(Van Mechelen, 1992). The cornerstones of the training were throughout the
intervention sufficient warming-up before training, muscle
stretching after training, not too fast progressing intensity,
variation in training sessions, and finally, no competitive
elements were included in the training programme.
Women rated both their perceived health and fitness and men
their perceived fitness better after the intervention. The
fact that low back and knee symptoms did not show any increase
after the training programme, certainly has contributed to
the increase in self- rated health and fitness among the participants.
Participation in an intensive training programme may have
influenced the exercisers' subjective perception of health
and fitness; after the intervention many participants probably
felt healthier and more fit than before because of a change
in lifestyle, even if the change were temporary. Similar effects
of participation in fitness programmes have been previously
reported (Shephard and Bouchard, 1995;
Sörensen et al., 1997).
The positive feedback concerning health and fitness in this
study was in line with previous observations (Allison, 1996;
Manderbacka et al., 1999),
indicating that health behaviours are associated with self-rated
health; subjects with low physical activity at leisure, and
with unhealthy dietary habits, as well as smokers show poorer
In a recently published study of Anton et al. (2004),
the authors gave support to the hypothesis that the age-related
decline is greater in the more complex performances which
require more of power-type strength and greater neuromuscular
co-ordination. Therefore, in designing training programmes
for middle-aged and even older subjects, the participants'
current health status, training status, physical activity
and previous training background will give valuable information
for the purpose of making up an optimal training programme
with relevant training intensity for the target group, and
thereby preventing exercise induced injuries and musculoskeletal
symptoms. This background information also assists the training
instructor in individually optimising the intensity and progression
of the programme.
Adherence to the training programme
Although the power-type strength training programme was initially
unfamiliar and demanding in terms of intensity for most of
the participants, the dropout rate in the present study was
low, when compared with other studies, as reviewed by Robison
and Rogers (1994).
The dropout rate was greatest during the first weeks, which
is in line with several earlier studies, as analysed by Dishman
and Buckworth (1996).
In the present study, one possible explanation for dropping
out at an early stage is the discrepancy between the subject's
own, probably unrealistic expectations of training and the
actual training with all its potential inconvenient side effects.
The discrepancy between the actual exercising and the image
of exercising may also be of practical nature, e.g. the lack
of time, the lack of means of transportation, and the family-related
demands certainly have an effect on training adherence.
The low training adherence among the unemployed was an interesting
finding in the present study. Unemployment may reduce a subject's
capacity to meet these different types of problems. Possibly
reduced capacity to handle problems is supported by a large
empirical study of Whooley et al. (2002) in which depressive
symptoms were associated with subsequent unemployment and
loss of income. Unemployment can be a powerful stressor (Ezzy,
Physical exercise has been shown to reduce anxiety in unemployed
(Grönningsäter and Fasting, 1986),
therefore it is important to encourage the unemployed to adopt
and maintain regular physical exercising. In the present study,
the unemployed smoked more than the employed, and the unemployed
dropouts smoked more and had more frequent knee symptoms than
the unemployed who completed the training programme. The unemployed
showing good adherence to the programme also perceived their
fitness and health better.
The higher training adherence among older participants may
be explained by the fact that they had more time to spend
in physical activities, and perhaps also a more realistic
picture of their own capacity to complete the intervention
programme. The latter aspect may partly explain why younger
female participants had lower adherence to this programme.
Evenson et al. (2002) suggested that the perimenopausal period
is a critical time at which focused and tailored physical
interventions may help women to adopt physical activity patterns
from the earlier periods of life in order to be physically
active in postmenopausal period.
With increasing age, health-related problems begin to appear
and individuals start paying more attention to health issues.
In general, the most common exercise motives both in men and
women are those connected to health and fitness. Women are
more often than men motivated by health and stress reduction,
and ageing adults seem to be more interested in exercising
for stress reduction and social reasons (Duda and Tappe, 1989;
Male dropouts presented a lower rate of physical leisure activities
than the men who completed the programme; the most popular
exercise and leisure activities were walking, home gymnastics
and gardening. Probably subjects with these light and moderate
activities had already done their contemplation of the exercise
(Prohaska and Clemente, 1983)
and were better prepared for the intervention programme, which
in turn resulted in higher training adherence.
The exercisers more frequently trained for mental satisfaction,
compared with the dropouts; otherwise the training motives
were similar for all groups and both genders. It can be assumed
that achieving mental well-being in connection with physical
training needs previous positive physical and mental experiences.
This may be reflected in the better adhering participants'
answers concerning their motives. The training motives may
be linked with the reasons given by the dropouts, such as
"lack of motivation" and "lack of time".
To be motivated to train physically, one needs to internalise
the subjective benefits.
There were no differences in health or in musculoskeletal
symptoms between the exercisers and dropouts. Therefore, the
main reasons for their different adherence behaviour are probably
the present physical activity at leisure, the perception of
one's own health and fitness, and the socio-economical status.
When interpreting the results of this study, one must also
take into consideration that many factors that are essential
for the evaluation of the reasons for dropping out were not
included in the study, for example, education, level of income,
marital status, children and several other environmental factors.
Previous studies indicate that exercise adherence is lower
among people with low education and low income (Yen and Kaplan,
Trost et al., 2002).
evaluation of the study
subjects in this study were heterogeneous concerning employment
status; both blue-collar and white-collar professions were
represented (majority of participants were engaged in light
office work), the age among subjects ranged from 29 to 69
years, and the exercise history also varied greatly. Most
of the participants were sedentary when the intervention started
and had been so for years. The type of training used in the
intervention is very demanding for the neuromuscular system,
and therefore it is important to keep the (duration of) exercise
bouts short and take care of sufficiently long recovery times
(at least 2-4 minutes). These criteria were difficult to meet
in the training programme for practical reasons: training
was conducted in exercise classes of 10-20 subjects, with
differing individual training experience and status within
each exercise class. The recovery times were for some of the
subjects almost always too short.
The evidence of the intervention would have been more powerful
if the study population had been randomised. However, randomisation
would have been very difficult in this study in which the
subjects were asked to perform physical exercises with maximal
effort. Volunteers in physical training programmes usually
have a positive approach, but the subjects may also have expectations
concerning the effort they have made, and this may cause a
bias, compared with the non-training controls, who may have
quite opposite attitudes to physical strain.
The number of non-training controls should have been greater
in this study. The small number of non- training controls
does not allow any larger generalisations. As a matter of
fact, a kind of simple group-wise randomisation took place
when the population was divided into No Load versus Light
Load groups; before the training started, the participants
did not know whether they would have external loads totalling
2.2 kg in their ankles or not during the power-type strength
At baseline, the subjects were similar in anthropometrical,
some behavioural, and habitual characteristics, and also in
the distribution of low back symptoms. However, the classification
of participants according to the attendance rates is a limitation
of the study, because some unmeasured characteristics of those
with high and those with low attendance rates may have been
missed. It can be assumed that subjects with high adherence
were more motivated to try harder and achieve higher improvements
in measurements. This sub-grouping of the subjects may also
have caused some disadvantages. The number of subjects in
some sub-groups became small, resulting in a lower statistical
power. Sub-grouping was justified by the fact that the participants
adhered differently to the training, and by the aim of investigating
the outcome of exercise dose vs. response.
Unfortunately, the subjects did not keep a diary of their
physical activities besides the training programme. That would
have been very helpful for achieving greater accuracy of the
training dose versus response analysis. As it now stands,
the minimum training dose is known, but the dose vs. response
is not accurate in those participants who exercised in their
leisure time more than the programme required.
The effects of power-type strength training were measured
by numerous and various methods, including semi-objective
and subjective measurements. This was done for obtaining a
comprehensive picture of the changes after the power-type
strength training intervention, not only changes in leg and
trunk muscle performances. The measurement methods used in
this study were all validated: vertical squat jump (Bosco
et al., 1982;
Moir et al., 2004),
20 metre running time (Mero et al., 1981;
Moir et al., 2004),
maximal anaerobic cycling test (Rusko et al., 1993;
Rusko and Nummela, 1996;
and standing long jump are widely used in testing physical
performance, especially among sports athletes. Also, the questionnaires
on perceived health, fitness and physical activity, and musculoskeletal
symptoms (Kuorinka et al., 1987,
Wolinsky and Johnson, 1992)
have been shown to be valid. All possible interfering factors
were, however, not included in the study. After the initial
measurements, the subject should have been measured again
after four weeks, before the training started, for controlling
the effects of the measurement. Muscle strength for the leg
muscles should have been included in the measurements, as
it was done for the trunk muscles. The leg muscle strength
would have been a reference parameter for the various power-type
strength measurements of leg muscles. Also, participants should
have been measured approximately six weeks after the training
started for controlling the neural effects in performances.
Training in exercise classes was supervised by the one and
the same instructor, and there were three to four exercise
classes training simultaneously.
This research was needed for planning and designing training
programmes that are both sufficient in intensity for achieving
training effects and safe enough to keep exercise induced
injuries and musculoskeletal symptoms at a low level. It was
also important to find out what are the motives of middle-aged,
sedentary men and women to exercise and by what means their
exercise adherence could be maintained. The daily activities
of the subjects in this target group often include little
of physical activities both at work and at leisure. Further,
the combination of sedentary lifestyle with normal ageing
process will inevitably decrease their functional capacity,
and various diseases may appear with increasing age and sedentary
For further research, the effects of power-type strength training
should be investigated preferably by randomised controlled
trials. Also, it should be examined whether the intensity
of this type of training could be increased in sedentary,
middle-aged subjects without increasing the injury risk or
musculoskeletal symptoms. The motivation for training in higher
intensity programmes should also be considered.
main conclusion of this study is that power-type strength
training is to be recommended for middle-aged men and women.
The training effect seems to be sufficient; training frequency
should be at least twice a week for achieving visible training
effects. The training programme presented here is simple and
practical to carry out among middle-aged, sedentary people.
The outcome of this study may be of assistance in planning
and designing training programmes for middle-aged and even
older subjects. With increasing age, rapid force production
is important for the performance of daily activities and also,
e.g., in preventing of falling.
In addition, the study shows that training improves power-type
strength performances in leg muscles, and a small progression
with light external loads (totalling 2.2 kg) in ankles increases
the efficiency, especially in vertical squat jump and in anaerobic
capacity of leg muscles. The improvements in other performances
than those mentioned were moderate.
The trunk muscle flexion and extension measurement proved
to be a reliable method for assessing the maximal angular
velocity of the trunk muscles. This intervention indicates
that power-type strength training improves the angular velocity
of trunk flexion and extension, provided that the training
frequency is at least twice a week.
As a whole, this study showed the feasibility of group based
power-type strength training for sedentary middle-aged men
and women. Perceived health and fitness increased among the
subjects who completed the training programme. The relatively
low incidence of training induced injuries and the unchanged
or decreased level of musculoskeletal symptoms during the
training indicate the feasibility of the programme.
The adherence to the programme was acceptable, especially
among women older than 50 years, among the employed men and
women, and among the non-smokers. The main reasons for dropping
out were lack of motivation and lack of time. The subjects
who completed the programme perceived their fitness and health
better after the training programme.
work was carried out at the Research and Development Centre
of the Social Insurance Institution in co-operation with the
University of Kuopio. I wish to express my sincere respect to
the former Director General Pekka Tuomisto and the other members
of the Board of the Social Insurance Institution, my former
superiors at Social Insurance Institution Director Mikael Forss,
PhD, Professor Esko Kalimo, PhD, and Professor Jorma Järvisalo,
MD. I thank the staff in the Research and Development Centre
for the support they gave to me. Several persons have contributed
to the different phases of my work and I wish to express my
profound gratitude to all of them. I also express my gratitude
to the Department of Physiology at the University of Kuopio
for providing a flexible possibility participating in master's
programme and in doctoral programme in exercise medicine.
I express my gratitude to my present superiors at National Public
Health Institute, Professor Arpo Aromaa, MD, the chief of the
Department of Health and Functional Capacity and Mr Antti Jula,
MD, PhD, the chief of Laboratory for Population Research for
supporting me in this study with their encouragement and by
providing facilities to complete this thesis.
My deepest gratitude to my two supervisors, Ms Sirkka Aunola,
PhD and Docent Heikki Pekkarinen, MD, PhD, for their expert
guidance, encouragement and tiredless support during all phases
of this study.
I wish to thank Professor Ari Heinonen, PhD, and Docent Antti
Mero, PhD, the official reviewers of my manuscript for their
rapid communication and constructive evaluation.
I owe my sincere gratitude to Docent Erkki Alanen, PhD, for
his valuable expert help in statistical work and for his advice
and insightful comments during the preparation of this work.
I warmly thank also my other co-authors, Ms Sirkka-Liisa Karppi,
MSc, Ms Pirjo Lehto, MSc, Mr Kari Mäentaka, MSc (Eng) and Ms
Tiina Nordblad, PT for pleasant collaboration and valuable advice
during my work.
I wish express my gratitude to Docent Markku T. Hyyppä, MD,
PhD, for discussions to help me to understand better many aspects
of the scientific research.
The staff of the Laboratory Department has made the most valuable
contribution to this research work. I sincerely thank all of
them, particularly the nurses Ms Sirpa Reiman-Kiiski, Ms Ritva
Läärä and Ms Mailis Äyräs, and the physicians Mr Hannu Karanko,
MD, Mr Antti Mikola, MD, and Docent Asko Seppänen, MD, PhD and
Mr Turkka Koivusaari BSc (Eng), for technical support.
I am very grateful to Ms Tuula Aaltonen, MSc, and Ms Arja Kylliäinen
for performing statistical analyses quickly and precisely, and
to Ms Kylliäinen for various kinds of assistance in data processing
and preparing study reports.
I sincerely thank Ms Marja Heinonen and Ms Riitta Nieminen for
careful drawing of the figures and the make-up of this thesis.
I am grateful to Ms Lea Heinonen-Eerola, MA, for revising the
English language of my manuscripts in both the original study
reports and this thesis.
I wish to thank the personal of the library in Social Insurance
Institution and National Public Health Institute for kind help
in obtaining the literature.
I wish to thank all those who have contributed to this study
for their collaborative work and useful advice. It is my pleasure
to thank Ms Taina Alikoivisto, Docent Jukka-Pekka Halonen, MD,
PhD, Mr Olli Impivaara, MD, PhD, Mr Erkki Kronholm, PhD, Docent
Jouko Lind, PhD, Docent Jukka Marniemi, PhD, Mr Reijo Rosvall
and Ms Mariitta Vaara, MSc, and Ms Eija Viholainen.
I thank Ms Riitta Ahjokivi, MSc and Mr Markko Keto-Tokoi for
their excellent work in supervising and instructing the participants
in exercises, and I also thank all the volunteer subjects, who
participated in the study and made this work possible.
I am also grateful to my brother Jorma of his valuable advice
during the study, and the support of his family is also warmly
Finally I owe my warmest thanks to my wife Arja, for her love
and patience in our everyday life, and to our dear son Miikka
who always reminds me what is real important in life.
The financial support from the Social Insurance Institution
of Finland is gratefully acknowledged.
Employment: Senior Researcher, National Public Health Institute,
Department of Health and Functional Capacity, Population Research
Degree: PT, PhD
Research interests: Exercise physiology, muscle function,
functional capacity, rehabilitation (especially Multiple Sclerosis).