TRAINABILITY OF YOUNG ATHLETES AND OVERTRAINING
Children's Health and Exercise Research Centre, School of Sport and Health
Sciences, University of Exeter, UK.
15 March 2007
Journal of Sports Science and Medicine (2007) 6, 353 - 367
Google Scholar for Citing Articles
|Exercise adaptations to strength, anaerobic and aerobic training
have been extensively studied in adults, however, young people appear
to respond differently to such exercise stimulus in comparison to
adults. In addition, because overtraining in young athletes has received
little attention, this important area is also discussed. Resistance
training in children can be safe and effective. It has the potential
to improve sport performance, enhance body composition and reduce
the rate of sport incurred injury. Furthermore, with the appropriate
stimulus, prepubertal and adolescent athletes can show significant
increments in muscle strength (13 - 30%). Children can improve anaerobic
power (3%-10% Mean Power and 4%-20% in Peak Power), although the mechanisms
responsible for the improvements in children remain unclear. Children
show a 'reduced' trainability of peak VO2 in comparison
to adults. Nevertheless, their aerobic power is trainable, with improvements
reported at approximately 5%. Moreover, improvements in other variables
like exercise economy or lactate threshold may occur without significant
changes in peak VO2 The limited evidence available indicates
that overtraining is occurring in young athletes (30% prevalence),
highlighting the importance of further research in to all the possible
contributing factors - physiological, psychological and emotional
- when investigating overtraining.
WORDS: Prepubertal and adolescent athletes, trainability, mechanisms,
resistance training, anaerobic training, aerobic training, overtraining.
Can children be physically trained? Is training healthy for children?
Can a child become overtrained? These are just some of the questions
that exercise and sports scientists have debated over in the past;
however conclusive answers to these issues remain elusive.
As Armstrong and Welsman, 2002
state, "children are not mini-adults" indicating that
our understanding of the exercise physiology of an adult cannot
just be scaled down and applied to children; Indeed the very process
of growth and maturation complicates our understanding of the trainability
of children as this process mimics the effects of training (Baxter-Jones
et al., 1995;
Naughton et al., 2000)
and thus needs to be accounted for when determining the success
or failure of an exercise training programme. Additionally with
the majority of studies being cross-sectional in nature it is difficult
to partial these aforementioned maturational effects on the training
response. With these caveats understood the available literature
suggests that children can show improvements in strength (Falk and
Payne et al., 1997;
aerobic fitness (Baquet et al., 2003;
Baxter-Jones et al., 1993;
Kobayashi et al., 1978),
and anaerobic fitness (Rowland, 2005;
with exercise training.
TRAINABILITY DURING CHILDHOOD
the increasing participation in youth sports (American Academy
of Pediatrics 2000;
Baxter-Jones and Mundt, 2007),
young athletes, like adults, strive to achieve higher performances
through improving their health and fitness, with resistance
training being used to enhance an athlete's performance in
sport (Kraemer et al., 1989).,
The development of muscle strength through resistance training
in children is still the subject of some debate and criticism.
In the past, clinicians would consider resistance training
contraindicated in children due to the risk of epiphyseal
plate injury and because it was believed that children were
incapable of increasing their strength or muscle mass through
such exercise (Myer and Wall, 2006).
Although early studies suggested that resistance training
did not lead to significant improvements in strength (Vrigens,
subsequent studies have suggested that children are indeed
able to increase their strength (Blimkie, 1992;
Blimkie and Bar-Or, 1996;
Mahieu et al., 2006;
Myer and Wall, 2006;
Ozmun et al., 1994).
Muscular strength can be defined as the maximal force or tension
a muscle or a group of muscles can generate at a specified
velocity (Knuttgen and Kraemer, 1987).
The positive effects of resistance training on adult athletes
have been well documented in the literature (Chilibeck et
Sailors and Berg, 1987;
Staron et al., 1994);
isometric strength training in adult men can result in increases
in strength of 92% and in muscle size of 23% (Ikai and Fukunaga,
dynamic weight training can increase strength by 30% (Moritani
and DeVries, 1980).
Both types of training are also effective in increasing strength
in pre-pubertal children and adolescents, with both groups
also showing considerable improvements (Rowland, 2005; Tolfrey, 2007).
The findings of two meta-analyses on resistance training in
children support these claims. Falk and Tenenbaum (1996)
analysed 28 studies involving girls and boys under the age
of 12 and 13 years, respectively, with nine of these studies
subsequently included to calculate effect size (ES). Findings
indicated an overall mean ES of 0.57 (0.12), suggesting a
significant improvement in strength is achievable in children.
The typical gains in muscle strength were approximately 13
- 30%, greater than that which should be expected from growth
and maturation. It was interesting to note that the largest
absolute and relative gains in strength were seen in the youngest
aged children (Falk and Tenembaum, 1996).
Similar findings were observed in the other meta-analysis
by Payne and colleagues (1997), which included 28 studies and reported a mean ES of
0.75 (0.57). Participants were categorized into "younger"
or "older" groups based on the average age at peak
height velocity (PHV). The authors concluded that, regardless
of participant or study characteristics, children and youth
can demonstrate considerable increases in muscular strength
as a result of resistance training (Payne et al., 1997).
Although the overall picture suggests that children can in
fact improve muscular strength, the studies on which these
conclusions are based are not without their problems; a lack
of control for a learning effect that could account for early
strength gains, not reporting adherence rates, non-randomization
into the training and control groups, and a over-reliance
on boys as study participants. Finally, apart from 2 studies
that were longer than 20 weeks, all other studies were of
relatively short duration, making it difficult to delineate
whether a dose response factor operates with resistance training.
do children get stronger?
The mechanisms underlying strength improvements and muscle
hypertrophy in adults arise through an interaction between
neural and hormonal mechanisms. However, in the pre-pubescent
population, muscle hypertrophy is not believed to be the primary
factor in strength improvement. When an adult undertakes a
resistance training programme, the gains in strength that
arise in the first three to five weeks occur primarily through
neural mechanisms, after this period, increased muscle fibre
size is the main contributor to strength improvements (Tolfrey,
It is still unclear whether children's improvements in muscle
strength are accompanied by increases in muscle size. Vrijens
compared strength development in prepubescent and post-pubescent
boys who trained isotonically 3 times per week for eight weeks.
Using roentgenography to measure muscle cross-sectional areas
(mCSA), no significant changes were observed in either arm
or thigh mCSA in the pre-pubertal boys (1.2% and 0.6% increments
for thigh and arm muscles, respectively), whereas muscle area
increased significantly for both limbs in the adolescent group
(8.5% and 6.2% increments for thigh and arm muscles, respectively).
The lack of change in mCSA in prepubertal children is supported
by Sailors and Berg, 1987, who determined muscle size using anthropometric and somatotype
techniques, but failed to show any training-induced muscle
hypertrophy even though a significant increase in strength
was reported. Comparable results have also been reported in
adolescent females (Blimkie et al., 1993).
Clearly the hormonal environment plays a key role in determining
the magnitude of increase in muscle size. Although testosterone,
Growth Hormone (GH), Insulin-like Growth Factor I (IGF-I)
and insulin all influence muscle hypertrophy during growth
and maturation, their interaction with strength training in
children is not clear. It is thought that until the concentration
of testosterone in particular, starts increasing at puberty,
significant muscle hypertrophy is unlikely to occur with resistance
training in prepubertal subjects (Vrigens, 1978).
However, Mersh and Stoboy, 1989 reported significant strength-induced increases in muscle
size after 10 weeks of isometric training in prepubertal boys.
The trained leg increased in strength by 35% to 40% and in
mCSA by 4% to 9%. Likewise, Fukunaga et al., 1992 studied 50 boys and girls aged 6.9 to 10.9 years on a
12-week resistance-training programme, which resulted in significant
improvements in mCSA. This was particularly true in the older
children, in whom the average increase in mCSA was 15.1% for
the boys and 12.8% for the girls. Such observations suggest
that although muscle hypertrophy can occur, other factors,
beyond changes in muscle size, predominantly account for increases
in strength during pre and early puberty (Tolfrey, 2007).
Limited information is available on neural adaptations to
resistance training in young athletes, but the data suggests
that these play a significant role (Ozmun et al., 1994; Ramsay et al., 1990). While the hormonal influence on muscle tissue is important
in developing the potential for muscular strength, neuromuscular
interactions are essential for the functional development
of muscle tissue (Kraemer et al., 1989; Sale, 1988).
Based solely on the lack of evidence for muscle hypertrophy
seen in some studies, the strength gains in preadolescent
boys after resistance training have often been attributed
to undefined neurological and neuromotor adaptations (Blimkie,
1992; Blimkie and Bar-Or, 1996; Sailors and Berg, 1987). Such conclusions are supported by the work of Ozmun
et al., 1994, who used electromyography (EMG) to measure strength training-induced
changes in neuromuscular activation. They tested 8 prepubertal
boys who followed an 8-week-resistance-training programme
and observed improvements in isometric and isokinetic arm
strength of 22.6% and 27.8%, respectively. At the same time,
EMG amplitude rose by 16.8%, supporting the possibility of
improved neural activity within the muscle being trained.
Another technique to assess neuromuscular changes is the twitch
interpolation technique, which determines the contribution
of changes in motor unit activation (MUA) to muscle force
development; that is, a brief electrical stimulus is applied
to the muscle in order to evoke contraction. Ramsay et al.,
1990 tried to identify specifically whether changes in muscular
strength were due to hypertrophy and / or neurological activity.
After undertaking a resistance-training programme with 13
boys for 20 weeks the experimental group increased their strength
compared to the control group; training resulted in 13.2%
and 17.4% increase in MUA for elbow flexors and knee extensors,
respectively. Furthermore, the same authors also assessed
twitch torque (TT), a measure of intrinsic muscle strength,
using the same technique; they observed improvements of approximately
30% in evoked TT on the elbow flexors and knee extensors.
Since there were no corresponding increases in muscle size,
the resulting data suggested an improvement in twitch-specific
tension (strength per muscle cross sectional area) (Ramsay
et al., 1990).
In addition biomechanical factors such as changes in pennation
angle of the muscle, the level of skill and motor coordination,
the balance between synergist and antagonist muscle activity,
enhanced stores of ATP / CP (adenosine triphosphate / phosphocreatine),
improved glycolytic capacity and elevated psychological drive,
all may contribute to improving strength during a training
programme (Blimkie, 1992; Rowland, 2005),
and therefore require further study.
Muscle hypertrophy appears to be a consistent outcome of strength
training throughout adolescence in males, although in adolescent
females a more variable response and smaller increases in
muscle size are found. Also, the relative gains in lean mass
that can accompany resistance training during adolescence
and preadolescence are smaller than the relative gains in
strength (Blimkie and Sale, 1998).
There have been few studies that have looked at differences
in training induced strength improvements between genders,
but it appears that both sexes respond similarly. Kirsten
(1963) (cited in Blimkie, 1992),
studied the effects of 15 weeks of isometric training in groups
of boys and girls (ages 11-12, 13-14 and 15-16 years), and
found significant increases in strength in only the two older
age groups for the girls, and only in the oldest age group
for the boys - however the magnitude of change, when evident,
was similar between the sexes. Other work showed that 12 weeks
of dynamic strength training in prepubertal boys and girls,
resulted in similar increases in strength in both sexes (McGovern,
1984; cited in Blimkie, 1992).
The gender differences in muscle size are small until mid-puberty,
increase progressively with age during late puberty and adolescence,
and reach peak difference during early adulthood (Malina and
As discussed previously, strength training-induced muscle
hypertrophy has not been consistently observed in either prepubertal
or pubertal boys (Blimkie and Sale, 1998;
Fukunaga et al., 1992;
Mersh and Stoboy, 1989).
Due to a lack of investigations on girl's resistance training
responses there are few available data to make confident gender
comparisons, but training induced muscle hypertrophy has also
been reported in girls. Fukunaga (1976) (cited in Blimkie
and Bar-Or, 1996)
reported an 8.3% increase in upper arm lean area in 13-year-old
adolescent girls engaging on a 3- month isometric strength-training
programme. Conversely, Blimkie and colleagues (1996),
employing 26 weeks of heavy resistance training in adolescent
girls (14-17 years) observed significant strength gains but
found no increase in anthropometric measurements of the upper
arm girth or quadriceps mCSA determined by computerized tomography.
It appears that if muscle hypertrophy is seen after resistance
training it is a sex independent response (Blimkie et al.,
of strength gains
How persistent are resistance training- induced strength gains
in children after they stop training? Only few studies have
investigated this topic on adults and even fewer in children.
In adults, strength training-induced increases in muscle size
and neural drive appear to decay during detraining about the
same rate as they increase during training. Furthermore, detraining
in adults is characterized by a relatively rapid reduction
in neuromuscular activation and a more gradual reduction in
muscle size (Narici et al., 1989).
To date, only one study by Blimkie and colleagues (1989)
looked at the effects of 8 weeks of detraining in prepubertal
boys following 20 weeks of resistance training. The training-induced
strength gains regressed toward the growth-adjusted control
level during the detraining period, suggesting that alike
with adults, training adaptations are reversible (Blimkie
et al., 1989).
of resistance training
It appears that developing strength during childhood will
lead to improvements in sport performance (Faigenbaum, 2000;
Kraemer et al., 1989),
and diminish susceptibilities to injuries (American Academy
of Pediatrics, 2000).
Furthermore, resistance training has also been recommended
for girls as an osteoporosis preventive measure (Myer and
Strength training can be a safe and effective method of conditioning
for children and adolescents (Coutts et al., 2004;
Myer and Wall, 2006).
However, training programmes performed without proper supervision
can greatly increase the risk of musculoskeletal injuries
such as fractures of the epiphyseal plate, herniated intervertebral
disks, and lower back injuries in both children and adolescents.
However, beneficial adaptations in ligament tendon and bone
strength may reduce injury risk in a young athlete's chosen
sport (Fleck and Falkel, 1986).
Lenhard and colleagues (1996)
reported that adding a resistance training programme to a
male soccer team significantly reduced injury rates. Moreover,
Hejna and Rosenberg, 1982
reported that young athletes (13-19 years) who included resistance
training as part of their exercise regimen demonstrated decreased
injuries and spent less time in rehabilitation when compared
with their team mates (Hejna and Rosenberg, 1982).
Thus, resistance training may be considered not only a safe
activity but it also may reduce injuries in competitive athletes.
training programme prescription
The component parts of the training programme will play a
great influence on the extent to which a child improves strength;
those are: the resistive load, the number of repetitions used,
the number of sets, the rest in between repetitions and groups
of repetitions (sets), session frequency and the total length
of the programme. Furthermore, for the programme to be safe
and healthy, children should not engage in high-intensity
efforts (e.g. maximal or near maximal lifts with free weights
or weight machines), should avoid isolated eccentric training,
and exercise on a circuit-training programme in order to stimulate
possible cardiorespiratory benefits (Kraemer et al., 1989).
Young athletes should be allowed 2 to 4 weeks of adaptation
to basic resistance training that should consist of a minimum
of 2 sessions per week, with a limited number of sets (one
or two), basic exercises, moderate loads (12-15 RM) and adequate
recovery (approximately 48 hours). This is important whether
it is the first time an individual has weight trained or a
new programme is being started after weeks or months of no
training (Kraemer et al., 1989;
Furthermore, if experienced, children may be able to exercise
at higher intensities and with a higher frequency of training
per week; indeed high intensity and volume training has been
shown to be effective in children (Mersh and Stoboy, 1989;
Nielson et al., 1980).
Again, extremely high-intensities (very high loads) should
be avoided, especially during prepubertal years, as should
eccentric-type of training until the later stages of adolescence
(Blimkie and Bar-Or, 1996).
The data challenges the myth that resistance training in children
is dangerous, may result in growth plate injuries and also
that it is ineffective because young athletes are unable to
increase their strength without the "necessary"
Both prepubertal children and adolescents can demonstrate
significant gains in muscle strength with resistance training
(between 13 - 30%).
Muscle hypertrophy is limited in prepubertal children, but
is more frequently observed from puberty onwards, and may
reflect changes in circulating concentrations of growth and
Independent of changes in muscle hypertrophy, neuromuscular
adaptations underpin increases in strength in young children.
Resistance training can be a safe and effective type of exercise
for young athletes if programmes are well designed and supervised
by knowledgeable personnel.
Strength training has the potential of improving sport performances,
enhancing body composition and reducing the rate of sport
injury and rehabilitation time following injury.
trainability of the anaerobic system in young people has received
less attention compared to strength and / or aerobic fitness.
Nevertheless, anaerobic capacity and anaerobic power can impact
sporting performance and therefore the trainability of these
attributes is of interest to coaches, athletes and sports
The anaerobic trainability of young people is difficult to
study given the many facets of performance and capacity for
short-term, maximal intensity activities. One reason for such
a paucity of data is that the equipment and protocols for
studying anaerobic performance are quite complex compared
to those used for strength programmes; the latter only requires
the measurement of force whereas the former calls for the
simultaneous measurement of force production throughout time
(Blimkie and Bar-Or, 1996).
In addition, ethical factors have limited our ability to quantify
changes in muscle glycolytic activity at the cellular level
in children. Thus, these enhancements are inferred from changes
seen from the product of their activity (i.e. peak power).
Complicating this further is the fact that power production
during tests such as the Wingate or the Force-Velocity test
are a composite of not just glycolytic activity rate, but
of other factors such as muscle size and neural activity.
Also, when assessing speed trainability and other short-term
activities like high jump or countermovement jump, the plasticity
of neuromuscular coordination and motor skills must also be
considered (Blimkie and Bar-Or, 1996;
Finally, different approaches have been taken during investigations
of anaerobic power, but the most common has been the use of
repetitions of short-term activities lasting from 5 to 30
seconds. These activities have mostly involved cycling and
running at maximal intensities, with participants being tested
on a cycle ergometer and treadmill, respectively (Blimkie
and Bar-Or, 1996; Rotstein et al., 1986; Sargeant et al., 1985).
children improve anaerobic performance with training?
Adult studies have demonstrated the trainability of anaerobic
power - improvements after training of around 12% in peak
power (PP), and 6-7% in mean power (MP) (Barnett et al., 2004; Nevill et al., 1998; Sharp et al., 1986). These training induced changes in power output arose
through augmented intramuscular levels of PC, ATP, and glycogen,
increased activity of anaerobic enzymes, hypertrophy of fast-twitch
muscle fibres, augmented lactate production at submaximal
and maximal intensities, and an improvement in performance
in short-burst activities (McArdle et al., 2000).
Enhanced power output in children does occur with training
Grodjinovsky et al. (1980) (cited in Tolfrey, 2007)
found that mean power (MP) and peak power (PP) tested on the
Wingate test, increased by 3.4% and 3.9% respectively, after
sprint cycling or sprint running training. The small magnitude
of gains may be attributable to the low duration of the training
(15 minutes per session over 6 weeks), however other studies
have also demonstrated that children can improve their anaerobic
power through sprint training; MP (10%) and PP (14.2%) (Rotstein
et al., 1986; Sargeant et al., 1985).
in anaerobic power with mixed-type training
Twelve-weeks of complex-training (using dynamic constant external
resistance and plyometrics) with early pubertal boys resulted
in improved anaerobic power, jumping, throwing and sprint
performance, and marked improvements in dynamic strength (Ingle
et al., 2006). Similarly, Sargeant et al., 1985 studied 13-year-old boys during an 8-week mixed training
programme composed of short-burst activities and aerobic exercises.
They observed an improvement in PP of 4.5% compared with an
average 1.2% increase in the control group.
in anaerobic power with aerobic training
Studies dealing with the effect of aerobic training on peak
power in children have generally provided concordant results.
McManus and colleagues (1997) engaged 12 young girls either in an aerobic cycling programme
of 8 weeks duration. They observed a 10% rise in peak VO2,
yet they also saw a 20% increase in Wingate PP alongside.
Although the differences in the magnitudes of the changes
are reflective of the specificity of the training type, this
suggests that a cross-training effect may occur in children
(McManus et al., 1997). Likewise, Obert and his co-workers (2001b)
also reported changes in anaerobic parameters measured on
the force-velocity test after a 13-week aerobic (interval
and continuous) running programme on prepubertal boys and
girls. Participants improved peak power by 23%, which was
mainly attributed to the increase in optimal force (17%).
Finally, a 7-week aerobic running programme with 20 girls
and 13 boys (training intensities of their maximal heart rate
(HRmax) of 78% to 95% HRmax), was able
to significantly increase maximal shuttle-running velocity
(Baquet et al., 2002).
Children seem therefore to be able to improve their anaerobic
power whether following a dedicated anaerobic training programme
or a mixed-type programme. These data help to support the
inference of children being metabolic non-specialists, but
care should be taken when interpreting these data since the
studies used a variety of training loads (duration, intensity
and frequency), employed differing methods to study anaerobic
system's responses to exercise (Wingate test, force-velocity
test, field tests, non-motorised treadmill, and isokinetic
dynamometer), conflicted training mode with testing mode,
failed to account for changes in anthropometric variables,
and mixed children of different maturities.
differences in anaerobic power
Studies looking specifically at gender differences in anaerobic
trainability in children are lacking. Though some studies
used both boys and girls as participants, subsequent analysis
on gender was not performed (Baquet et al., 2002; Bencke et al., 2002; Hawley and Williams, 1991; Obert et al., 2001a). Naughton and co-workers (1998) found male adolescents display a greater magnitude of
improvement in PP and MP after training, but no comparative
data for prepubertal children are available.
factors explain the changes in anaerobic power in children?
Information relating anaerobic metabolic changes with training
in young athletes is lacking, due in part to the practicalities
of measuring metabolic responses directly (e.g. enzyme activity
and muscle fibre histology), which are dependent on invasive
muscle biopsies. However, the limited data available do however
provide a window to attempt to explain the changes seen in
children's anaerobic power.
Rate-limiting enzymes and lactate
Fournier and colleagues (1982) studied the alterations in muscle PFK (phosphofrutokinase)
and fibre area in 6 adolescent boys (16-17-years-old) after
having undergone a sprint-training programme for 3 months.
After obtaining pre- and post- biopsies form the vastus lateralis,
no changes in muscle fibre size or percentage were reported
(Fournier et al., 1982). However, PFK concentration increased 21% over and above
that which could not be attributed to growth.
Despite possible glycolytic enzymatic changes-with training,
children do not normally show increments in maximal blood
lactate levels after anaerobic exercise training. Prado, 1997 studied 12 healthy boys (age 10) and 12 adult males (age
24) in a 6-week swimming training programme (3 times per week).
The training consisted exclusively in anaerobic series of
25m, 100m and a 45 second maximal swim distance. Adults improved
their performance in the 25m test and the 45s test after the
6 weeks, whereas no effect of training was observed on the
boys. Maximal lactate concentrations were significantly lower
in children than adults, but no changes were observed in maximal
lactate with training within either group. Such findings do
however cast doubt on the appropriateness of using maximal
lactate as a surrogate measure for glycolytic activity.
Sargeant et al., 1985 observed significantly greater improvements in lean body
mass (4.8% increase), and upper leg muscle (9.7% increase)
in the experimental group compared to the controls after 8-weeks
of mixed training; indicating the importance of muscle mass
in explaining training induced improvements in power output.
Thigh muscle volume has been shown to be the strongest significant
explanatory variable of PP in 12 to 14-year-old boys and girls
(Santos et al., 2003), but qualitative muscular and neurological factors are
also implicated (Obert et al., 2001a).
A study involving 11-13-year old Swedish boys who participated
in a 4-year sprint-training programme investigated the link
between anaerobic power and muscle morphological / histochemical
adaptations. Improved muscular endurance (50 all-out repetitions
of isokinetic knee extension) were associated with an increase
in mCSA, even though no changes in muscle fibre-type composition
occurred (Jacobs et al., 1982).
In another study addressing muscle fibre characteristics and
physical performance in athletic boys (sprinters, weight lifters
and tennis players) concluded that the size and morphology
of muscle fibre type are related to and influenced by the
characteristics of the sports being performed (Mero et al.,
The use of phosphorus nuclear magnetic resonance spectroscopy
(31P-NMRS) as a non-invasive technique to measure
intracellular inorganic phosphate (Pi), PC, ATP, allows us
a possible insight into muscular glycolytic activity. Kuno
and colleagues (1995)
reported a similar PC/(PC+Pi) ratio between untrained and
trained 12 to 17-year-old adolescents after performing exhaustive
exercise. However, the same ratio was higher when compared
to adults, reflecting a 'poorer' anaerobic response in young
populations (Kuno et al., 1995).
However this conclusion has been challenged by recent findings
in which a group of prepubertal and pubertal female synchronized-swimmers
had their glycolytic responses to short-term high-intensity
exercise assessed in their gastrocnemius and soleus muscles
using 31P-NMRS. The authors found no significant differences
for pH values or Pi/PC ratio and stated that the glycolytic
system of physically active children appeared to be independent
of maturity (Peterson et al., 1999).
training programme prescription
Based on the available literature is seems that an anaerobic
training programme can be successful on inducing positive
biochemical and performance adaptations in young children.
Nevertheless, the problems described for the limitations of
training studies also apply to the implementation of an anaerobic
programme; methodological concerns on the evaluation of performance
on anaerobic tests, and difficulties on sustaining the motivation
and interest of young children and adolescents. Therefore,
in order to keep the motivation levels high an anaerobic programme
that includes both aerobic and short-burst activities may
As such, an anaerobic programme should include a minimum of
3 sessions per week, of 30 minutes to hour duration. Children
should engage in short high intensive activities (not less
than 90% of maximal effort), like sprint running, jumping,
throwing, plyometrics, sprint cycling, interspersed with submaximal
aerobic activities. Finally, the duration of the anaerobic
exercises should aim 20-30 seconds (Armstrong and Welsman,
Improvements in MP ranging from 3% to 10% and in PP from 4%
to 20% are reported in children, showing that the anaerobic
fitness is to some degree trainable.
There is a lack of knowledge about the mechanisms responsible
for the improvements seen in anaerobic fitness in children
- muscle size, fibre type, neurological and biochemical changes
may underlie the response, but require future research.
adults, training-induced adaptations to aerobic training have been
extensively studied, and it is well documented that adults can improve
their cardiorespiratory (aerobic) fitness levels if they are given
the appropriate training stimulus. The focus of child-based studies
has largely centered upon improving fitness levels for either athletic
performance or for its relationship with health outcomes. Typically
the training programme design used with children mirrors that used
for adults (Rowland, 1985),
whether this is appropriate or not remains to be clarified, but
evidence indicates that higher intensities may have to be used to
initiate a response in children (Baquet et al., 2003;
Massicotte and Macnab, 1974).
Unfortunately, despite the abundant research on aerobic training,
the relationship between exercise training and adaptations in aerobic
metabolism are still not well understood in prepubertal and early
pubertal children (Baxter-Jones and Mundt, 2007;
Early investigations have generally assumed that young children
would have minimal or no response in aerobic fitness (peak VO2)
to endurance training, which was attributed to either a high inherent
level of physical activity (American Academy of Paediatrics, 1976;
Yoshida et al., 1980),
or to some unexplained limitations in the biological responsive
mechanisms related to maturation (Katch, 1983).
This apparent "inferiority" of children to develop aerobic
fitness was thought to be a reflection of the maturational differences
between pre- and postpubertal children. The 'trigger hypothesis'
implied that there would be a time (trigger point) in a child's
life - namely puberty - before which the effects of training would
be negligible, or would not occur at all. The prepubertal hormonal
environment of low GH and sex steroid concentrations were considered
not suitable to bring about measurable improvements in physiological
function and thus, enhanced aerobic fitness with training.
how much can children improve aerobic fitness?
According to the literature it is believed that children show a
reduced magnitude of improvements in aerobic fitness after endurance
type training than that seen in adults. Young adults typically show
an increase in peak VO2 of around 15-20%, although a
large intra- subject variation can be present (Bouchard et al.,
in children however this is reduced to <10%. The meta-analysis
of Payne and Morrow (1997)
analysed the data from 69 studies (of which 28 met the inclusion
criteria) that were either a cross- sectional comparison between
trained and untrained children or a pre-test/ post-test design.
Greater differences between trained and untrained participants (Effect
Size (ES) of 0.94 ± 1.00) were seen, but less than a 5% change in
peak VO2 (approximately 2mL·kg-1·min-1)
were noted in the pre-post studies (ES 0.35 ± 0.82). More recently,
Baquet et al., 2003
argued that improvements in peak VO2 of around 5-6% are
observed when the data are analysed independently by sex or pubertal
status. These authors also stated that when only studies that reported
significant changes were considered, peak VO2 improvements
rose to 8-10% (Baquet et al., 2003).
In line with the two previous studies, Rowland, 2005
compiled a series of what he considered to be well-designed investigations
in children and stated that the improvements in aerobic power were
indeed quite small, with the greatest improvement being 10%, but
the average change being 5.8%.
Is seems that children need to train at a higher exercise intensity
to elicit increases in aerobic fitness than for adults. Heart rate
has normally been used as a marker of training intensity, with recommended
intensities between 60-90% of HRmax, or 60% of HR reserve
(difference between resting and maximal HR) for adults. However,
the same target heart rates do not seem to be effective in children
as a sufficient exercise intensity is a necessary stimulus in order
to see improvements in peak VO2 (Rowland, 2005).
A study by Massicot and MacNab (1974)
involving three separate groups of nine boys (11-13 years) set different
training intensities for each group. Participants trained at heart
rates of 130-140, 170-180, and 150-160 beats·min-1, and
were compared to a matched control group. After having been matched
for baseline peak VO2 and then randomly assigned to the
four experimental groups, the boys undertook six weeks of aerobic
training. The results showed that only the boys who exercised at
the highest intensities (above 170 bts·min-1 - at least
88% HRmax) showed an 11% increase in peak VO2.
Indeed as long as the training intensity is high enough, improvements
have been seen in both prepubertal and adolescent children., Baquet
and colleagues (2002)
looked at the effects of a 7-week (twice per week) high intensity
intermittent training programme on peak VO2 of prepubertal
boys and girls. Peak VO2 increased by 8.2% compared with
a 1.9% reduction in the 20 maturity-matched control participants.
The results demonstrated that prepubertal children can increase
peak VO2 with high intensity aerobic exercise. Also,
the fact that children only exercised two times during the week
comes to reinforce the importance of intensity as a major stimulus
for peak VO2 improvements.
At present, there are few studies, which have addressed sex differences
in the trainability of aerobic fitness in children, with the majority
of studies recruiting boys as participants. Single sex studies using
girls however have reported that significant improvements in peak
VO2 are possible (McManus et al., 1997),
akin to that seen in boys. The data from those studies that have
directly compared the sexes suggest that boys and girls demonstrate
similar responses in aerobic trainability (Baquet et al., 2003;
Baxter-Jones et al., 1993),
even though boys' peak VO2 appears to be slightly higher
than girls (Naughton et al., 1998;
Obert et al., 2003).
Obert et al., 2003
had 10 girls and 9 boys participate in a 13-week endurance training
programme (3 X 1 hour per week, intensity: 80%HRmax)
and found that significant improvements in peak VO2 were
observed for both groups; boys increased peak VO2 by
15% and girls by 8%. Similar findings were reported by Baquet et
9.5% increase in peak VO2 for the prepubertal boys being
not significantly different from the 7.2% increment observed in
pre-pubertal children improve aerobic fitness?
To return to the hypothesis of Katch, 1983
discussed previously, it appears that prepubertal children are indeed
able to show increased aerobic fitness levels with training (Baquet
et al., 2002;
Kobayashi et al., 1978;
McManus et al., 1997;
Obert et al., 2003; Tolfrey, 2007). Indeed, work by Danis et al. (2003) with sets of prepubertal and circumpubertal monozygotic
twins - one acting as the control, the other undergoing endurance
training for 6 months, 3 times per week, with the intensity set
at 85-120% of their lactate threshold (LT) - saw improvements only
in the prepubertal children and not the circumpubertal twins, clearly
contradicting the postulations of Katch. Furthermore, one investigation
looking at the effects of two types of training (cycling and sprint)
during 8 weeks (3 times per week), on aerobic power of prepubertal
girls showed significant increases in peak VO2 (McManus
et al., 1997).
The literature suggests that prepubertal and adolescent athletes
are aerobically trainable, nevertheless, one should not disregard
Katch's hypothesis since prepubertal children seem able to improve
aerobic fitness to a lesser magnitude compared to adults.
mechanisms affecting aerobic fitness
What potential reasons have therefore been given to explain the
reduced magnitude of the training response seen in children compared
Adult data indicates that changes in the concentrations of hormones
such as GH, IGF-I, testosterone, oestrogen are responsible for the
anabolic effects seen with exercise training. It is not clear however
how these hormones are affected by endurance training in children
with much of the information being extrapolated from studies with
adults and animals (Boisseau and Delamarche, 2000).
It appears however that testosterone concentration is markedly up
regulated with training in children; sex-related increases in VO2,
muscle size and strength, and maximal arterio-venous oxygen (A-VO2)
difference, seem to be related with pubertal increases in testosterone.
The time when testosterone starts increasing during puberty matches
the age when aerobic trainability improves significantly (Rowland,
Mero and colleagues (1990)
measured resting serum testosterone, before, during and after a
year of training in 11-12-year-old boys. The boys engaged in different
activities like long distance running, sprint running, tennis and
weight lifting. After the training period testosterone was almost
3 times higher in the training group compared to the untrained boys,
and the mean testosterone level had approximately doubled after
a year of training. It was concluded that the increases in physical
performance and fitness were a direct result of the training induced
enhanced testosterone concentration even in early puberty (Mero
et al., 1990).
Furthermore, there is evidence showing that testosterone levels
can rise during acute bouts of exercise in adults, although not
in prepubertal subjects (Fahey et al., 1979).
The cardiovascular characteristics of young adult endurance athletes
have been well described. These athletes typically show a peak VO2,
which is approximately twice as large compared to the sedentary
population, a reflection of a superior cardiac output (CO) resulting
from a greater left ventricular size and consequent larger SV (Faria
et al., 1989;
Wolfe et al., 1986).
Intervention studies confirm that SV and ventricular size are eminently
trainable in adults, with SV increasing by 10-30% with exercise
training (DeMaria et al., 1979;
Stratton et al., 1994;
Wilmore et al., 2001).
An increase in peak VO2 in adults is related to both
central (increased maximal CO) and peripheral adaptations in A-VO2
difference (Wilmore et al., 2001).
In children, however, less information is available on this topic.
Cross-sectional studies of trained and untrained children suggest
that cardiac size and function, thus ultimately SV, are greater
in trained children. Nottin and colleagues (2002)
found higher SV values in the trained cyclists compared to controls
and stated that these increases were influenced by factors such
as cardiac hypertrophy, augmented cardiac relaxation and possibly
expanded blood volume. Furthermore, similar findings have been reported
in trained versus untrained distance runners (Rowland et al., 1998).
Intervention studies also indicate that cardiac size and function
are modifiable with training in children. Early work by Erickson
and Koch (1973),
using dye dilution technique, measured the cardiovascular responses
of prepubertal boys (11-13-years-old) to 16 weeks of training. The
authors observed decreases in resting HR, increases in heart size
and peak VO2 at the end of the programme; the latter
related to the increase in SV rather than through an increased A-VO2
difference (Eriksson and Koch, 1973).
In agreement with earlier work, a recent study looking at cardiac
adaptations after a 13-week endurance training programme in prepubertal
boys and girls (10.5 ± 0.3 years), saw that peak VO2
increased by 15% and 8% in the boys and girls respectively. The
authors reported significant increments in SV (boys: +15%; girls:
+11%) in both sexes, with this being the strongest explanatory variable
for the increases in peak VO2 (Obert et al., 2003).
Testosterone affects aerobic fitness by affecting changes in heart
size (Janz et al., 2000). It has been shown that during puberty, the size of the
left ventricle in males increases at a faster rate than it does
in females (Hayward et al., 2001),
which could work as an advantage for males during exercise by enabling
increases in SV (stoke volume) and end-diastolic volume, and consequently
CO (cardiac output).
With no difference in maximal A-VO2 difference being
reported in either cross-sectional comparisons or intervention studies
in children, this indicates that central factors rather than peripheral
usage may determine training induced adaptations in aerobic fitness.
However it appears that the magnitude of change seen in cardiac
factors is slightly lower than seen in adults and may contribute
to the reduced aerobic trainability of children.
In adults, improvements in performance, lower submaximal exercise
lactate production, and greater reliance on fat metabolism due to
endurance training seem to be associated with an increase in mitochondrial
numbers within the skeletal muscle (Holloszy and Coyle, 1984).
In one of the few studies in children to assess the changes in oxidative
enzymes with aerobic training, Eriksson et al., 1973 looked at the effects 6 weeks of endurance training on
muscle metabolic profile in 5 prepubertal boys (11-13 years old).
Via a muscle biopsy, the authors observed an increase in the concentration
of the oxidative enzyme, succinicate dehydrogenase (SDH) of 30%
post training. Work by the same authors in adults, reported that
endurance athletes show greater levels of SDH (50% higher) when
compared to sedentary people (Eriksson et al., 1973). Moreover, it has been reported that the concentration
of another aerobic enzyme, isocitric dehydrogenase (ICDH), is higher
in children than typically found in adults and also that there is
a lower ratio of ICDH to PFK (Haralambie, 1982),
suggesting that children might be preferentially adapted to aerobic
metabolism. Arguably this may leave less scope to improve the aerobic
enzymatic profile of the muscle with training potentially explaining
the blunted training effect in children, but with such little data
derived from limited numbers of children this has to remain speculation.
fitness: A blunted response or too narrow view of the concept?
From the presented data it is clear that children can experience
improvements in cardiorespiratory function after exercise training,
although not to the same extent as adolescents or adults. The majority
of the studies report increments in peak VO2 typically
around 6%, with exceptional cases when studies demonstrate improvements
greater than 15%. However methodological flaws related with the
intensity used during the training study, initial level of fitness
of the subjects, lack of controls, a mismatch of training type with
testing mode (e.g. swim training with cycle testing), insufficient
training intensities, all possibly contribute to the reduced aerobic
Another issue related with studying aerobic fitness may be related
with to the over-reliance on using peak VO2 as a 'gold
standard'. What if the concept of aerobic fitness has not been interpreted
fully in children? Does focusing on changing peak VO2
provide too narrow a focus for what is meant by the term 'aerobic
trainability'? After all peak VO2 is only one component
of the factors that contribute to endurance exercise performance.
According to Bosh, 2006, misunderstandings surrounding scientific dogma may have
influenced sport scientists' interpretation of the evidence that
is used to extrapolate and generalize results. As such, because
studies mainly used peak VO2 as a parameter of evaluation
it is hard to ascertain if other changes in aerobic fitness were
Indeed adult data indicates that peak VO2 is of limited
value to athletes, because exercise scientists and coaches cannot
use it as a predictor for future performance, or for the prescription
of potentially "optimal" training (Bosh, 2006; Jones, 2006).
Although peak VO2 might show limited scope for change,
other physiologic parameters known to be related to aerobic exercise
performance such as lactate and ventilatory thresholds, exercise
economy, and VO2 kinetic response might have been altered
favourably (Jones, 2006; Jones and Carter, 2000).
The longitudinal studies on Paula Radcliff (Jones, 2006)
and Lance Armstrong (Coyle, 2005)
epitomize this; both these world class athletes showed a relatively
stable peak VO2 during long periods of their careers,
yet economy and performance enhanced significantly in the same time.
In children the data indicate similar adaptations are evident. Welsman
et al. (1997)
found no changes in peak VO2 in prepubertal girls after
endurance training; however a significant reduction in submaximal
exercise lactate levels were noted in these same children. Haffor
et al., 1990
noted an improvement in lactate threshold in a group of 11-year-old
boys after interval training yet peak VO2 was unchanged
(Haffor et al., 1990).
Studies on young children have also seen improvements in running
economy and performance set against no changes in peak VO2
(Daniels et al., 1978;
Krahenbuhl et al., 1989).
Peak VO2 can significantly improve with training in children
by approximately 5%.
Why children show a 'reduced' trainability of peak VO2
in comparison to adults is still not clear.
Improvements in exercise economy, lactate threshold and performance
may occur without any change in peak VO2.
IN YOUNG ATHLETES
development practices and structures direct children to specialize
in one or two sports from an early age, especially if they seek
to aspire to perform at the very highest levels. The "catch
them young philosophy" that matched the beliefs of many coaches
who think that in order to achieve success at senior level it is
necessary to start intensive training well before puberty (Baxter-Jones,
2007; Baxter-Jones and Mundt, 2007),
has meant many of our youngsters are training intensively and for
considerable hours by the time they become adolescents. This is
of great importance as they are often asked to train at levels that
could be considered exhaustive even for adults, but also they are
assumed to be capable of withstanding the physical and psychological
pressures that participation in elite sport can entail (Borms, 1986;
Kentta et al., 2001).
It is this success driven environment, that potentially causes the
athlete to engage in very hard training without being aware if it
really is of benefit for his / her own performance (Kentta et al.,
In addition to the long hours of intensive, repetitive training
and strict dietary regimens, it is also important to consider the
impact on the young athlete's socio-cultural life; separations from
the family to train or compete away from home, the impact on academic
performance and the reduced opportunities to make school friends
etc (Coakley, 1992;
Kentta et al., 2001;
Consequently, the combination of heavy training, inadequate recovery
and limited social support networks for the young athlete can result
in overtraining in even young and aspiring elite athletes (Coakley,
Kentta et al., 2001).
It is therefore important that sport scientists, coaches, medics
and parents start to become aware of the potential negative health
implications (physical, physiological and psychological) of such
training practices in young athletes (American Academy of Pediatrics,
According to Kreider et al. 's (1998) definition of overtraining, this state results
from an accumulation of training and non-training stressors that
has a detrimental long-term effect on performance, with a recovery
period that may take several weeks or months. Overreaching, which
is considered to be a normal process of training, is defined as
an accumulation of training and non-training stressors that lead
to a short-term decrease in performance, which can be overcome with
recovery lasting days or a few weeks (Kreider et al., 1998). However overreaching may develop into overtraining
if sufficient recovery time is not given, indicating that overreaching
and overtraining are just two ends of the same continuum.
Overtraining is fundamentally an imbalance between training fatigue
and non-training stressors, and recovery. Furthermore, it is associated
with a variety of symptoms that often vary considerably across individuals
(Kentta et al., 2001). The latter has led to disagreements as to which signs
and symptoms need to be present for an athlete to be defined as
being overtrained or overreached (Meesuen et al., 2006; Uusitalo, 2006). A recent position statement by the European College
of Sports Sciences tried to provide clarity to the definition by
recommending that overreaching was divided into two different stages,
functional overreaching and non-functional overreaching, with the
latter eventually leading to the overtraining syndrome (Meesuen
et al., 2006). However, the statement did not provide guidance over
the duration of each stage (Uusitalo, 2006), making it hard to distinguish which state is the athlete
in and also, when does functional overreaching turn into non-functional
overreaching and ultimately overtraining? With disagreement over
not only the presenting symptoms of but also the definition of overreaching
and overtraining, the simplicity of the categorizations provided
by Kreider et al., 1998
seems more useful to employ.
in adults and young athletes
Overtraining syndrome has been extensively studied in adult athletes,
and therefore data on its prevalence are known. Morgan and colleagues
reported that approximately 10% of male collegiate swimmers indicated
being overtrained, although rates of up to 21% have been noted in
other swimmers (Hooper et al., 1995;
O'Connor et al., 1989).
The signs and symptoms of overtraining appeared in more than 50%
of professional soccer players during a 5-month competitive season
(Lehmann et al., 1992),
and 33% in basketball players during a training camp of 4 weeks
(Verma et al., 1992).
In two separate research studies in elite US distance runners, Morgan
et al. found that 60% of women and 64% of men reported being overtrained
at some point in their career (Morgan et al., 1988b;
Morgan et al., 1987b).
Importantly, the rate of overtraining occurrence dropped to 33%
when non-elite women runners were considered (Morgan et al., 1987b),
which is indicative of the close relationship between performance
level and the prevalence of overtraining.
While overtraining is acknowledged to be of concern for athletes
both in endurance and non-endurance sports (Kentta et al., 2001;
Kreider et al., 1998),
less data are known regarding incidence rates in individual sports
compared to team sports. The few studies available report incidence
ranging from 10-64% in individual sports and between 33-50% in team
sports (Hooper et al., 1995;
Morgan et al., 1988a;
O'Connor et al., 1989).
overreaching and overtraining prevalent in young athletes?
Very few investigations have been directed to young athletes and
therefore, it is not known whether similar responses to chronic
over-exercising in adults are evident in children. Recently a study
involving adolescent swimmers (13-18 year old) looked at the prevalence
of overtraining across different countries (Japan, USA, Sweden and
Greece) and found that 35% had been overtrained at least once (Raglin
et al., 2000). Kentta and colleagues (2001)
observed higher incidence rates for individual sports (48%) compared
with team sports (30%) and less physically demanding sports (18%).
In addition, in 1992, Coakley identified 15 adolescents who had been overtrained
during their careers (ages ranged from 15 to 19 years); the author
concluded overtraining was grounded in the social organization of
sport and recommended changes in the organization of high performance
sports; Also psychodoping was acknowledged as a social problem that
restricts athletes from creating a "healthy" identity
due to their lack of control over their own lives (Coakley, 1992).
and symptoms in adult athletes
A considerable number of studies have investigated the common signs
and symptoms reported in athletes from a range of different sports.
Fry et al.'s (1991) review listed more than 90 different symptoms that are
reported by overtrained athletes. Unfortunately, such a long list
makes it difficult for a coach or an athlete to know which signs
or symptoms to be concerned about, but further complicating the
picture is the large interindividual variability found within athletes
practicing the same sport (Verma et al., 1992).
One of the main complaints from athletes is a decrease in performance
(Budget, 1998), coupled with chronic fatigue and apathy (Armstrong and
VanHeest, 2002), which will often be ignored. Nevertheless, the responses
of athletes to overtraining have essentially been measured from
2 categories of symptoms: physiological and psychological. Several
physiological markers have been proposed as important and potential
parameters for the diagnose of overtraining such as: decreased or
suppressed levels of immunoglobulin A (IgA) (Gleeson et al., 1999; Gleeson and Pyne, 2000; Ring et al., 2005), decreased salivary testosterone to cortisol ratio (Passelergue
and Lac, 1999), increased salivary cortisol (O'Connor et al., 1989),
decreased heart rate variability (Hedelin et al., 2000;
Pichot et al., 2002),
increased catecholamines (Hooper et al., 1995).
However, some of the parameters, like hormonal markers, should not
be used as a single measure, since they show a very high variability
(Urhausen and Kindermann, 2002).
As example, it has been proposed that a decrease in cortisol levels
occurs in the more chronic state of overtraining (Lehmann et al.,
whereas an increase would represent an acute higher physiological
strain (Kirwan et al., 1988).
There is unfortunately no single practical, valid and reliable physiological
marker that can be used to enable a clear and quick diagnoses of
athletes who are entering this state (Kentta et al., 2001).
Nevertheless, some symptoms appear to be more frequently reported
than others; such as a higher incidence in infectious disorders
(upper respiratory tract infections), loss of appetite, unexpected
weight loss, sleep disturbances and emotional disturbances (Armstrong
and VanHeest, 2002;
Fry et al., 1991;
Morgan et al., 1987a; Raglin et al., 2000).
and symptoms in young athletes
Although few investigations have collected data on athletes in regards
to overtraining, there is some evidence suggesting that the signs
and symptoms in young athletes are typically the same or similar
to the ones found in the adult population. The mentioned cross-cultural
study performed on swimmers found that the highest complaint from
swimmers was primarily an increased perception of effort, followed
by feelings of heaviness (Raglin et al., 2000), which resembles the results from another study on young
elite athletes (Kentta et al., 2001). Also, swimmers who reported to be unmotivated had
higher levels of mood disturbances at all assessment points compared
with overtrained swimmers who retained their incentive to train
(Raglin et al., 2000). The study by Raglin and colleagues (2000) further reported more symptoms associated with overtraining
like muscle soreness, sleep disturbances and loss of appetite. Furthermore,
athletes were also asked to report additional symptoms during the
overtrained periods; they found these to be essentially of psychosocial
nature, i.e. social problems (family, boyfriend / girlfriend, coach
or friends), negative feelings like decreased interest in training
and competition and frustration to continue training. Finally, many
other psychological problems have also been described like athletes'
decreased self-confidence and ability to focus, short temper, heightened
levels of irritability, depression, sadness, and elevated levels
of perceived stress (Kentta et al., 2001).
Since 20 years of research on overtraining indicates that objective
physiological markers have generally not proven useful to monitor
training and performance, therefore the need to increase athletes'
self-awareness, i.e. making them more aware of physical or psychological
stress has been highlighted (Kentta and Hassmen, 1998;
Kentta et al., 2001).
This latter issue is important as clinical depression has been reported
in overtrained athletes (Hooper et al., 1995; Kentta et al., 2006; Morgan et al., 1987a;
In regard to the psychological factors associated with overtraining
in youth sports, the use of the POMS (profile of mood states) scale
that assesses relevant emotional shifts in tension, depression,
anger, vigour, fatigue and confusion has proven useful. As overtraining
progresses the deterioration of positive moods and the increase
in negative moods can clearly be tracked by POMS. Furthermore, the
necessity to increase the awareness of youth sport coaches about
this issue has been stressed elsewhere (Hollander et al., 1995).
Likewise, parents can unduly pressurize their child by overemphasizing
winning, holding unrealistic expectations, criticizing them and
pushing them to play. All of these factors reiterate the need for
parents to be educated about their critical role in their child's
sporting development (Gould and Eklund, 1991).
It has been recently recognised that the overtraining signs and
symptoms are actually very similar to the ones encountered in the
condition traditionally known as depression (Armstrong and VanHeest,
According to the American Psychiatric Association, there are two
sub-types of this condition, but concerningly the one that most
closely resembles overtraining syndrome is known as major depression
(Yudofsky and Hales, 1992).
Major depression affects an individual's thoughts, feelings, physical
health, behaviour and ability to function on daily activities. Furthermore,
it involves at least two weeks of depressed mood or lack of interest
on nearly all life activities, with individuals reporting similar
signs and symptoms to the ones seen in overtraining - problems with
sleep, lack of appetite, irritable mood, loss of body weight, loss
of motivation (Yudofsky and Hales, 1992).
Finally, overtraining syndrome shares similar brain structures,
endocrine pathways and immune responses to the ones reported for
major depression (Morgan et al., 1987a; O'Connor et al., 1991).
In fact, Morgan and colleagues (1987a)
reported that approximately 80% of athletes with overtraining had
a psychopathology similar to people with psychological depression.
Moreover, even highly motivated athletes will have difficulties
coping with the way they perceive poor performance, because of their
desire to perform well and win (Coakley, 1992;
One of the reasons for the frustrations seen in these athletes who
are performing badly, has to do with the pressure they put on themselves
to achieve their goals (Hanna, 1979).
The frustration due to the lack of performance typically drives
the athlete to further increase the amount of training that he /
she is doing, which just exacerbates the situation by increasing
physical and emotional fatigue, with a consequent worsening in performance
(Kentta et al., 2001).
This cycle (process) manifests itself by changes in mood, sleep
disturbances, losses in appetite and body weight, and an increase
in depressive symptoms, eventually leading to depression (Armstrong
and VanHeest, 2002).
The limited data available suggests overtraining is prevalent in
young athletes, therefore finding ways to identify those children
with the condition or at risk of becoming overtrained, supported
by constructive ways to treat, or better still avoid, overtraining
would be invaluable.
Accordingly, it seems appropriate to address this topic by taking
a multidisciplinary view (Birrer and Levine, 1987;
Kentta et al., 2001);
we believe that psychobiologic parameterization of training can
offer an effective monitoring strategy for child athletes in the
detection and prevention of overtraining. Future overtraining research
should try to incorporate the collection of emotional parameters
questionnaires such as POMS, Training-Induced Distress scale (Raglin
and Morgan, 1994),
or overtraining questionnaires (Maso et al., 2004)
and, at the same time collect objective physiological markers such
as immunoglobulins (IgA), hormonal parameters (testosterone and
cortisol), heart rate variability etc. By so doing, this will allow
us to understand how variations in measures of mood correlate with
physiological markers (Kentta and Hassmen, 1998),
but also view the problem holistically. Treatment strategies can
therefore be focused not just on physiological recuperation but
also address the personal identity and emotional issues in parallel.
The limited available evidence seems to point to an occurrence of
overtraining in young athletes around 30% and therefore should be
investigated more extensively in the future.
Overtraining and clinical major depression share many similarities,
therefore overtraining should be studied by acknowledging this perspective.
Collection of physiological, psychological and emotional parameters
may be useful to improve our understanding of overtraining and to
provide new perspectives on how to look at this important issue
in child athletes.
Children's strength, anaerobic and aerobic power is trainable,
although the improvements may be smaller than seen in adults. The
underlying mechanisms responsible remain to be conclusively determined,
but improvements in non-invasive technologies will aid our ability
to investigate these issues for children in the future. Overtraining
seems to be present in some young athletes, yet we need more research
to allow us to recognize the key signs / symptoms along with identifying
the central determining factors to allow us to help prevent this
condition arising in the first place.
Children's strength, anaerobic and aerobic power is trainable,
although the improvements may be smaller than seen in adults.
can demonstrate significant gains in muscle strength with resistance
training (13 - 30%).
in mean power (3 - 10%) and peak power (4 - 20%) are reported
fitness can improve with training in children by approximately
available evidence indicates an occurrence of overtraining in
young athletes of around 30%.
Employment: PhD student at the Children's Health and
Exercise Research Centre.
Degree: BSc, MSc.
Research interests: Overtraining in young athletes.
Employment: Senior Lecturer and an Associate Director
of the Children's Health and Exercise Research Centre.
Degree: BA(Ed), PhD.
Research interests: Overtraining in young athletes
and children's cardiac function.