EFFECT OF DIFFERENT REST INTERVALS ON THE EXERCISE VOLUME COMPLETED
DURING SQUAT BOUTS
Department of Physical Education and Sports Science, Razi University, Kermanshah,
13 June 2005
Journal of Sports Science and Medicine (2005) 4, 361
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purpose of this research was to compare effect 3 different rest intervals
on the squat volume completed during a workout. Twenty college-aged
men volunteered to participate in this study (age 20.73 ± 2.60 years;
body mass 80.73 ± 10.80 kg). All subjects performed 3 testing sessions,
during which 4 sets of the squat was performed with 85% of a 1RM load.
During each testing session, the squat was performed with a 1, 2,
or 5-minute rest interval between sets. Volume was defined as the
total number of repetitions completed over 4 sets for each rest condition.
Statistical analysis was conducted separately for the squat. One-way
repeated analyses of variance with Bonferroni post hocs demonstrated
significant differences between each rest condition for both exercises
tested (p < 0.05). The 5-minute rest condition resulted in the
highest volume completed, followed in descending order by the 2- and
1-minute rest conditions. The ability to perform a higher volume of
training with a given load may stimulate greater strength adaptations.
WORDS: Strength training, recovery, squat, recruitment.
you intend to use added strength will dictate how you should train.
Training is specific in terms of angle, range of motion and even
velocity of contractions (Sharkely, 1990).
Strength training programs can be designing to emphasize muscular
strength, power, hypertrophy, or endurance (Kraemer et al., 2002).
When designing strength training programs, many variables such as
intensity, volume, frequency, repetition, velocity and rest between
sets must be considered (Baechle et al., 2000;
Kraemer et al. , 2002).
The manipulation of training variables as mentioned above is determined
by the goals of the program and the needs of the individual. Mistakes
in any of these variables in the progression of a program could
theoretically result in an overtraining syndrome, therefore the
manipulation of these variables must be correct done (Kreider, 1998).
Training volume is a summation of the total number of repetitions
performed during a training session multiplied by the resistance
used. Training volume has been shown to affect neural (Hakkinen
et al., 1987;
hypertrophy (Dolezal, 1998),
metabolic (Collins, 1986),
and hormonal (Gotshalk, 1997;
responses and subsequent adaptations to resistance training.
The amount of rest between sets has been considered an important
factor that can be manipulated to fit the goal of a program this
factor significantly affects the metabolic (Kraemer et al., 1987),
hormonal (Kraemer et al., 1990;
and cardiovascular (Fleck, 1988),
responses to an acute bout during resistance exercise, as well as
performance of subsequent sets (Kraemer et al., 1997)
and training adaptations (Pincivero et al., 1997;
Robinson et al., 1995).
When training for increased strength, longer rest periods of 2 and
5 minutes have been recommended to allow for greater recovery and
maintenance of training intensity (Baechle et al., 2000;
Kraemer et al., 2002;
Willardson et al., 2005).
Previous studies have shown that the amount of rest between sets
has a significant effect on the total volume completed during a
workout, which may affect subsequent strength adaptations (Robinson
et al., 1995).
An investigation using the effect of a 3-minute rest interval versus
a 1-minute rest interval on the total number of repetitions completed
over 3 sets of bench press and leg press with a fixed 10 repetition
maximum (10RM) load. When resting was 3 minutes between sets, each
player was able to complete 10 repetitions for all 3 sets. However,
when resting was 1 minute between sets, a significant reduction
in the total number of repetitions was observed (p < 0.05), (Kraemer
et al. , 1997).
One study examined the effect of 3 different rest intervals on the
total number of repetitions completed over 4 sets of squats with
85% of a 10RM load and reported that no significant differences
were observed among 3 different rest intervals [The 3 rest intervals
included (a) a post- exercise heart rate (HR) equal to 60% of age-predicted
maximum HR, (b) a timed 3-minute interval, and (c) a work : rest
ratio of 1 : 3] each rest condition for the total number of repetitions
completed. However, within each condition, the number of repetitions
performed for each set declined significantly between the first
and the fourth set (p < 0.05), (Larson et al., 1997).
Weir et al. (1994)
studied the effect of 4 different rest intervals on a repeated maximal
bench press. Each subject performed 2 maximal bench presses, separated
by a 1-, 3-, 5-, or 10-minute rest between sets. Results demonstrated
no significant differences between rest intervals in the ability
to perform a repeated maximal bench press (p < 0.05).
Finally, Willardson et al. (2005)
studied a comparison of 3 different rest intervals on the total
number of repetitions completed over 4 sets of squats with a 8RM
load, results demonstrated that the 5-minute rest condition resulted
in the highest volume completed, followed in descending order by
the 2- and 1-minute rest conditions. The ability to perform a higher
volume of training with a given load may stimulate greater strength
The results of these studies suggest that the repeatability of performance
over multiple sets is dependent on the amount of rest between sets
and the load being lifted. However to our knowledge, the impact
of 1, 2, or 5-minute rest interval on the squat volume completed
over 4 sets with 85% of a 1RM load has not been reported, And resistance-trained
athletes, such as bodybuilders or power- lifters, must perform exercises
at maximal or near maximal intensities with repeated efforts in
order to enhance muscular hypertrophy and/or strength. Recovery
between efforts for these athletes may be a critical issue for maximizing
performance; however, to our knowledge no investigations have examined
this issue. Therefore, the purpose of this study was to compare
the effects of 3 different rest intervals on the squat volume completed
over 4 sets with 85% of a 1RM load.
approach to the problem
A group of 20 college-aged men volunteered for this research study
(age, 21.53 ± 2.50 years; body mass, 77.83 ± 5.50 kg). All subjects
were classified as experienced recreational lifters by having consistently
performed a minimum of 3 strength workouts per week for the previous
2 years and none of the subjects had an experience with such training
styles before the study.
Data collection occurred over a period of 4 weeks with 1 testing
session each week. In the first session 1RM in the back squat exercise
was determined during preliminary testing. The squat was performed
in a power cage. The pins in the power cage were adjusted to allow
the subject to descend to the point where the tops of the thighs
were parallel to the floor. A successful parallel squat required
descending by flexing the knees and hips until the proximal head
of the femur reached the same horizontal plane as the superior border
of the patella and then 85% of a 1RM load was selected to purpose
the load used in testing. Warm-up consisted of performing 5-10 repetitions
at 40-60% of perceived maximum, a 3-5-minute rest and stretching
period, and the completion of 3-5 repetitions at 60-70% of maximum.
3 to 5 subsequent lifts were then made to determine the 1RM with
5 minutes of rest between lifts. An attempt was considered successful
when the movement was completed through a full range of motion without
deviating from proper technique and form. Spotters were present
to provide verbal encouragement and safety for the subjects. To
ensure that all subjects were moving at approximately the same velocity
for each repetition, each set was timed using a handheld stopwatch.
The spotter called out a cadence for the eccentric and concentric
phases of each repetition. The repetition velocity consisted of
a 3-second eccentric phase followed by a 1-second concentric phase.
During the next 3 testing sessions, 4 sets of the squat was performed
with a 1-, 2-, or 5-minute rest interval between sets. A counterbalance
procedure was used to determine the order of exercises and the rest
interval between sets for each testing session. Subjects were allowed
to continue with their normal workouts throughout the duration of
the study with the following exceptions: (a) subjects were instructed
not to perform the squat in their personal workouts, and (b) subjects
were instructed not to work out on the day of their scheduled testing
The results were analyzed with SPS11.5 statistical software. Values
from the different sessions were compared using a 1-way analysis
of variance (ANOVA) with repeated measures. The alpha level was
set at 0.05 in order for a difference to be considered significant.
Intraclass reliability was assessed between the last 3 testing sessions.
Volume was defined as the total number of repetitions completed
over 4 sets for each rest condition. When a significant session
effect was detected, a pairwise comparison of the sessions was done
using Bonferroni's post hoc test to identify significant differences
volume completed for the squat was significantly different between
the 1- and 5-minute rest conditions and between the 2- and 5-minute
rest conditions (p < 0.001, 0.002; see Table
1). However, the volume completed was not significantly different
between the 1- and 2-minute rest conditions (p = 0.190; see Table
1). Intraclass reliability for the squat was 0.97.
results demonstrated that, as the rest interval between sets increased,
the total number of repetitions completed also increased. There
was not a significant difference in the squat volume completed between
the 1- and 2-minute rest conditions (p = 0.190).
When lifting a submaximal amount of resistance, the slow and fast-twitch
muscle fibers are recruited but at first the slow-twitch muscle
fibers exert force and when the slow-twitch muscle fibers become
progressively fatigued, the fast-twitch muscle fibers continue to
produce sufficient force. Finally, when all available muscle fibers
are fatigued and cannot produce sufficient force, the set is ended
(Sale et al., 1987;
When considering the rest interval between sets, slow-twitch muscle
fibers would require shorter recovery due to their oxidative characteristics,
whereas fast-twitch muscle fibers would require longer recovery
due to their glycolytic characteristics (Weiss, 1991).
Because fast-twitch muscle fibers rely heavily on anaerobic glycolysis
for energy production, these fibers would accumulate higher levels
of lactic acid during high intensity exercise. The accumulation
of lactic acid has been shown to lower intracellular pH through
the dissociation of hydrogen ions (H+), which results in muscle
fatigue (Jones et al., 1986;
Taylor et al., 1990),
But Robergs, et al 2004
demonstrated that there is no biochemical support for lactate production
causing acidosis, Lactate production retards, not causes, acidosis.
Similarly, there is a wealth of research evidence to show that acidosis
is caused by reactions other than lactate production (Corey, 2003;
Every time ATP is broken down to ADP and Pi, a proton is released.
When the ATP demand of muscle contraction is met by mitochondrial
respiration, there is no proton accumulation in the cell, as protons
are used by the mitochondria for oxidative phosphorylation and to
maintain the proton gradient in the intermembranous space. It is
only when the exercise intensity increases beyond steady state that
there is a need for greater reliance on ATP regeneration from glycolysis
and the phosphagen system. The ATP that is supplied from these nonmitochondrial
sources and is eventually used to fuel muscle contraction increases
proton release and causes the acidosis of intense exercise. Lactate
production increases under these cellular conditions to prevent
pyruvate accumulation and supply the NAD+ needed for
phase 2 of glycolysis (Robergs et al. 2004).
It is important to note that lactate production acts as both a buffering
system, by consuming H+, and a proton remover, by transporting H+
across the sarcolemma, to protect the cell against metabolic acidosis.
The cause of metabolic acidosis is not merely proton release, but
an imbalance between the rate of proton release and the rate of
and removal. As previously shown , proton release occurs from glycolysis
(An accumulation of NAD+H+ produced by the Glyceraldehyde
3-phosphat dehydrogenas reaction) and ATP hydrolysis. However, there
is not an immediate decrease in cellular pH due to the capacity
and multiple components of cell proton buffering and removal. The
intracellular buffering system, which includes amino acids, proteins,
Pi, HCO3¯, creatine phosphate (CrP) hydrolysis, and lactate
production, binds or consumes H+ to protect the cell
against intracellular proton accumulation. Protons are also removed
from the cytosol via mitochondrial transport, sarcolemmal transport
(lactate¯/H+ symporters, Na+/ H+
exchangers), and a bicarbonate-dependent exchanger (HCO3¯/Cl¯).
Such membrane exchange systems are crucial for the influence of
the strong ion difference approach at understanding acid-base regulation
during metabolic acidosis (Kowalchuk, 1988;
However, when the rate of H+ production exceeds the rate
of the capacity to buffer or remove protons from skeletal muscle,
or when no enough time to buffer or remove H+ production, metabolic
acidosis ensues and results in muscle fatigue.
Short rest intervals of 1 minute or less have been shown to significantly
increase lactic acid levels during heavy strength training exercise
(Kraemer et al., 1987).
The time needed for lactic acid clearance following high-intensity
exercise has been shown to be 4-10 minutes (Jones et al., 1986).
In the current study, the 5-minute rest condition likely enough
time to uptake H+ and delayed fatigue, which allowed
subjects to complete a higher volume of training, versus the 1-
and 2-minute rest conditions.
The results of the current study were different from those demonstrated
by Kraemer (1997)
who found that when subjects rested 3 minutes between sets, they
were able to complete all 10 repetitions over 3 sets of bench press
with a 10-RM load. In the current study, subjects failed to complete
maximum repetitions over 4 sets of squat with 85% of a 10RM load,
even when resting 5 minutes between sets the repetitions decreases
from set-1 to set-4 (see Table
1). These differences in results may be accounted for by differences
in the training status of subjects.
The subjects utilized by Kraemer (1997)
were Division I football players accustomed to training with maximal
exertion over multiple sets. These subjects possibly had adapted
to the point that more repetitions were possible with shorter rest
intervals between sets. By contrast, the subjects in the current
study lifted recreationally and rarely trained with maximal exertion
over multiple sets. Larson et al. (1997)
utilized a sample of recreationally trained men and demonstrated
results that were consistent with the current study, with a significant
decline in the number of repetitions completed over 4 sets of squats
with 85% of a 10RM load.
Weir et al. (1994),
however, showed no differences in the ability to repeat a maximal
bench press following 1-, 3-, 5-, or 10-minute rest interval between
sets. A limitation of this study was that subjects only performed
2 sets with 1RM load. Had more than 2 sets been attempted, longer
rest intervals may have resulted in superior performance. In the
current study, subjects were able to maintain training volume to
the greatest extent when resting 5 minutes between sets.
The data in the present investigation are in agreement with several
other studies involving the use of 3 different rest intervals on
the squat volume (Kraemer et al., 1987;
Larson et al., 1997;
Willardson et al., 2005).
Although Robinson et al. (1995)
demonstrated that a 3-minute rest interval resulted in a higher
training volume, a longer rest interval may have produced an even
higher training volume and, consequently, greater strength gains.
The current study demonstrated a dose-response relationship between
the amount of rest between sets and the volume of training completed.
However, the practicality of longer rest intervals must also be
considered, and there may be a point of diminishing returns, yet
to be determined, where a longer rest interval yields no additional
squat is a common exercise prescribed in strength training programs.
When designing strength training programs, the amount of rest prescribed
between sets is likely dependent on the goal, the training status
of the individual, and the load being lifted. This study demonstrated
that a 5-minute rest interval between sets allowed for the highest
volume to be completed when training with 85% of a 1RM load. The ability
to perform a higher volume of training with a given load may stimulate
greater strength adaptations (Robinson et al., 1995).
A limitation of the current study was that gains in strength were
not measured and subjects were not separated into groups designated
by different rest intervals. Future research should continue to examine
changes in muscular strength, dependent on differences in the rest
interval between sets.
is no significant difference in the squat volume between the 1-
and 2-minute rest conditions.
5-minute rest interval between sets allow for the highest volume
to be completed when training with 85% of a 1RM load.
Employment: Assistant, Department of Physical Education
and Sports Science.
Research interests: Physiology of resistance training.