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Neuroendocrinol Lett 2018; 39(4):342–348
ORIGINAL ARTICLE
Neuroendocrinology Letters Volume 39 No. 1 2017
ISSN: 0172-780X; ISSN-L: 0172-780X; Electronic/Online ISSN: 2354-4716
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Pub Med / Medline: Neuro Endocrinol Lett
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Endocrine response to high intensity barbell
squats performed with constant movement
tempo and variable training volume
Michal W 1, Miroslav P 2, Michal K 1, Adam Z 1, Petr S 2
1 Department of Sports Training, The Jerzy Kukuczka Academy of Physical Education in Katowice,
Poland
2 Charles University in Prague, Faculty of Physical Education and Sport, Department of Sport Games,
Prague, Czech Republic
Correspondence to: Petr Stastny
Charles University, Faculty of Physical Education and Sport, Department of Sports
Games, Jose Martiho 31, 162 52 Prague, Czech Republic
.: +420 777198764; -: stastny@ftvs.cuni.cz
Submitted: 2018-08-24 Accepted: 2018-10-12 Published online: 2018-09-00
Key words: testosterone; cortisol; hypertrophy; resistance training; insulin-like growth
factor; growth hormone; time under tension
Neuroendocrinol Lett 2018; 39(4):342–348 PMID: 30531700 NEL39041814 © 2018 Neuroendocrinology Letters • www.nel.edu
Abstract
OBJECTIVE: Research indicates that among the many elements of resistance
exercise protocols, training volume and total training load are the key factors for
post-exercise increase in the secretion of testosterone (T), growth hormone (GH),
insulin-like growth factor (IGF-1) and cortisol (C). The aim of this study was to
determine the effects of resistance exercises with variable volume and constant
intensity and movement tempo on post-exercise concentrations of selected ana-
bolic and catabolic hormones.
MATERIALS AND METHODS: 28 experienced powerlifters (27.8 ± 2.9 years, with
6.64 ± 1.29 years of training experience, average body mass of 85.3 ± 3.3 kg and
body height of 165.8 ± 10.3 cm) who compete at the national and international
level performed three repetitions of barbell squats with a constant external load
of 90% 1RM and variable volume (3, 6 and 12 sets of squats) in three stages (pre-
exercise, immediately post exercise, and 1h after exercise) over three consecutive
weeks. Venous blood samples (10ml) were collected from the antecubital vein, to
determine pre- and post-exercise values of the following variables T, GH, IGF-1,
C, at rest, immediately after the cessation of the last set of squats, and after 60
minutes of recovery.
RESULTS: The T test showed that performing 6 and 12 sets resulted in increases
of post exercise GH (p<0.01). Performing 6 sets of squats resulted in post exercise
decrease (p<0.01) in IGF-1 and C. Performing 3 sets of squats resulted in immedi-
ate post exercise decrease of IGF-1 (p<0.01), which was not maintained 1h after
exercise. There were no other significant differences in analysed variables, with
the training volume of three sets of three repetitions, confirming previous data
suggesting that low volume is the limiting factor in increased post-exercise secre-
tion.
CONCLUS ION: This study demonstrated that in terms of endocrine response, the
optimal volume of high intensity strength exercise is six sets. Therefore, intention-
ally high volume (12 sets) or low volume (3 sets) are not an effective stimuli for
endocrine responses of trained individuals. The 6 sets of squats seems to drive
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Wilk et al: Response to barbell squat
hormonal responses of GH, C and IGF-1, which may
play a significant role in stimulating muscle growth and
tissue regeneration.
INTRODUCTION
Resistance exercises, especially those performed with
high intensity, cause significant endocrine changes,
both acute and chronic (Kraemer & Ratamess, 2005;
Uchida et al. 2009; Crewther et al. 2011). The endocrine
system is particularly sensitive to resistance exercise and
changes in anabolic and catabolic hormones have been
associated with the process of post-exercise rebuilding of
damaged muscle cells, and thus the magnitude and rate
of the post-exercise adaptation (Kraemer & Ratamess,
2005; Sedliak et al. 2007; Kadi, 2008). Hormones, par-
ticularly growth hormone (GH) and testosterone, have
a significant effect on the rate of protein synthesis, and
the type of substrates metabolized during and imme-
diately after exercise (Uchida et al. 2009). These hor-
mones also stimulate the activation and proliferation of
satellite cells which facilitate myofibrillar hypertrophy
(Kadi et al. 2005). GH has an anabolic effect on skeletal
muscles, stimulates the synthesis of proteins, facilitates
the transport of amino acids into skeletal muscles, thus
affecting hypertrophy of both Type I and Type II muscle
fibres (Hansen et al. 2001). Research has demonstrated
that blocking the effects of anabolic hormones reduces
the rate of adaptive changes and the effectiveness of
weight training programs (Kvorning et al. 2006). These
hormones play a significant role in mediating increases
in muscle mass and muscle strength (Kadi, 2008).
Some research indicates that among the many vari-
ables of strength training protocols, training volume
and total training load are key factors for post-exercise
increase in the secretion of various hormones (Krae-
mer et al. 1991). Other research results indicate that
duration of the force production and the length of
rest periods between sets are the most significant fac-
tors stimulating plasma and serum cortisol (C). These
hormonal responses are particularly intense in the case
of high-intensity, medium or high volume training
programs (Kraemer et al. 1991) and when the train-
ing protocol targets large muscle groups (Kraemer &
Ratamess, 2005). Research on the effects of strength
training on muscle hypertrophy showed an important
role not only of anabolic hormones like testosterone
(T), but also for growth factors, including the insulin-
like growth factor-1 (IGF-1). Serum IGF-1 elevations
are induced by strength training (Kraemer & Ratamess,
2005), but some studies suggested that this is the case
only when resting concentrations are low (Kraemer et
al. 1991). The divergent findings concerning the effect
of strength training on the process of adaptation and
response of the endocrine system may result from the
fact that most procedures did not specify the movement
speed for an exercise or the whole strength training ses-
sion. Only a few publications have analysed the effects
of movement tempo (cadence) on adaptive processes
in terms of strength, power, muscle hypertrophy or
endocrine responses (Wilk et al. 2018a; Headley et al.
2011; Hatfield et al. 2006; Sakamoto and Sinclair 2006;
Hunter et al. 2003; Keeler et al. 2001; Westcott et al.
2001). Repetition speed is the only variable which has
not been widely explored scientifically with respect to
adaptation and response of the endocrine system. In
most studies, the tempo of performing strength exer-
cises is volitional, according to the natural movement
rhythm. Studies have found that the lower the move-
ment speed the more intensive decline in the generated
muscle force (Hutchins 1993, Westcott et al. 2001, Krae-
mer et al. 2002). Wilk et al. (2018b) showed that the
movement tempo in strength training impacts train-
ing volume, both in terms of repetitions and total time
under tension (TUT). The optimal volume and inten-
sity of training loads in resistance exercises that may
most effectively stimulate the anabolic hormones while
diminishing the secretion of catabolic ones has not been
determined. This may be due to numerous factors such
as movement speed for an exercise, age, sex, training
experience, type of muscular contractions used which
complicate this issue. Additional factors include type
of equipment, diet, supplementation and how these
factors interact with genetic endowment (Wilk et al.
2018c). Exceeding the optimal training volume causes
the anabolic hormone peak to occur during training,
and continuation of exercise results in an excess con-
centration of catabolic hormones (Viru & Viru, 2004;
Uchida et al. 2009; West et al. 2012).
The aim of this study was to determine the effect of
variable volume in squat exercise with constant intensity
and constant tempo on post-exercise concentrations of
selected anabolic and catabolic hormones and growth
factors (GH, T, IGF-1 and C). An additional objective
was to determine the range of training volume, which
elicited the greatest anabolic hormone secretion while
limiting the increase in C.
MATERIALS AND METHODS
Experimental Approach to the Problem
All testing was performed in the Strength and Power
Laboratory at the Jerzy Kukuczka Academy of Physical
Education in Katowice. The experiment was performed
following a randomized cross sectional design, where
each participant performed a familiarization session
with a1-RM test and three different testing protocols
a week apart. During the experimental sessions, sub-
jects performed barbell squats at low volume - 3 sets
(LV3); medium volume - 6 sets (MV6); high volume- 12
sets (HV12). In each set 3 repetitions were done using
90% 1RM and a 2/0/3/0 tempo. Subjects were required
to refrain from resistance training 72 hours prior to
each experimental session, were familiarized with the
exercise protocol and were informed about the benefits
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Wilk et al: Response to barbell squat
and risks of the research before expressing their consent
for participation in the experiment.
Subjects
Participants for this study were 28 experienced power-
lifters who competed at the national and international
level. The age of the subjects was 27.8 ± 2.9 years, with
6.64 ± 1.29 years of training experience, average body
mass of 85.3 ± 3.3 kg and body height of 165.8 ± 10.3
cm. The participants were allowed to withdraw from
the experiment at any moment and were free of inju-
ries. The study protocol was approved by the Bioeth-
ics Committee for Scientific Research, at the Academy
of Physical Education in Katowice, Poland, according
to the ethical standards of the Declaration of Helsinki,
2013. Participants were instructed to maintain their
normal dietary habits over the entire study period and
did not use any dietary supplements or stimulants for
the duration of the study.
Procedures
Familiarization session and one repetition maximum test
The participants arrived at the laboratory at the same
time of day (in the morning between 09:00 and 11:00)
and cycled on an ergometer for 5 minutes at an intensity
that resulted in a heart rate of around 130 bpm, then
performed a general lower body warm-up. Next, the
participants completed 15, 10, 5 and 3 barbell squat rep-
etitions using 20%, 40%, 60%, 80% of their estimated
1RM using a 2/0/2/0 cadence. Knee wraps were allowed
and three spotters were present at all times during the
testing protocol. The participants then executed single
repetitions using a volitional cadence with 5 min of rest
between successful trials. The load for each subsequent
attempt was increased by 5 kg, and the process was
repeated until failure.
Experimental sessions
The participants arrived at the laboratory in the morn-
ing (09:00 to 11:00 am). After completing the same
warm-up as in the familiarization session, they per-
formed 3 sets (LV3), 6 sets (MV6) or 12 sets (HV12) of
the squat with 90% 1RM (Table 1) using 2/0/3/0 met-
ronome guided cadence (Korg MA-30,Korg, Melville,
New York, USA). The time between experimental ses-
sions of training was one week. The participants were
verbally encouraged throughout all testing sessions. All
repetitions were performed without intentionally paus-
ing at the transition between the eccentric and concen-
tric phases.
Blood sampling and analysis
During the experiment, 10 ml venous blood samples
were collected from the antecubital vein to determine
pre- and post-exercise concentrations of T, GH, IGF-1,
and C at rest, immediately after the cessation of the last
set of squats, and after 60 minutes of recovery. Com-
mercially available radioimmunoassay evaluations
Table 1. The testing protocols applied during the experiment
Low volume
(LV3)
Medium volume
(MV6)
High volume
(HV3)
Load (%1RM) 90%1RM 90%1RM 90%1RM
Tempo 2/0/3/0 2/0/3/0 2/0/3/0
Set / repetition 3 / 3 6 / 3 12 / 3
Rest interval
between sets 5 min 5 min 5 min
were performed for the evaluation of T (DSL-4000),
GH (DSL-1900), IGF-1 (DSL-2800), and cortisol (DSL-
2100). The ICC for the biochemical analysis varied
from 0,88 to 0,99 for the 4 conducted test.
Statistical Analyses
Means, standard deviations, confidence levels and
standard errors were calculated for all measured vari-
ables, and all variables were tested for normality by the
quantile-quantile test. To identify significant group
by time interactions, t test for independent trials was
used for each dependent variable. When a significant
interaction occurred post hoc test by Rodger’s method
was performed for detecting differences among groups
(pair wise comparisons). Rodger’s method belongs to
the most powerful post-hoc tests for detecting differ-
ences among groups. This test protects against loss of
statistical power as the degrees of freedom increase. The
statistical significance was set at p ≤ 0.05.
RESULTS
All variables were normally distributed as determined
by the quantile-quantile test results (p > 0.05). Among
28 experienced powerlifters (N = 28), there were sta-
tistically significant differences of GH concentration in
MV6, between the mean post-workout values (1.278 ±
4.89 ηg/ml) and the mean rest value (0.393 ± 0.234 ηg/
ml) t(7) = 5.87, p ≤ .01, as well as between the value
obtained one hour after exercise (0.573 ± 0.347 ηg/ml)
t(7) = 5.01, p ≤ .01. Statistically significant difference
also occurred in GH during HV12, between the mean
post-workout value (1.141 ± 0.432 ηg/ml) and the mean
rest value (0.199 ± 0.171 ηg/ml) t(7) = 6.15, p ≤ .01, as
well as the value obtained one hour after exercise (0.293
± 0.137 ηg/ml) t(7) = 6.07, p ≤ .01. Therefore, we reject
the null hypothesis that there is no difference in con-
centration of growth hormone at rest and post-workout
in MV6 and HV12 training. For LV3 training, GH con-
centrations were not significantly different between
mean values at rest, post-exercise and after one hour of
recovery when LV3 was applied. Significant differences
were found just for GH with MV6, and HV12 (Figure 1).
With regard to testosterone, no significant differ-
ences in concentration were observed as a result of
training volume at any time point. Therefore, we fail to
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Wilk et al: Response to barbell squat
Fig. 1. The average concentration of the growth hormone at various levels of
training volume. **p<0.01.
Fig. 2. The average concentration of the testosterone at various levels of training
volume.
reject the null hypothesis that there is no difference in
concentration of testosterone between training volume
at each time point (Figure 2).
For IGF-1, there were no significant differences in
HV12 between the mean rest concentration and the
post-exercise value. In the moderate volume trial, sig-
nificant differences were found between the mean rest
value (657.29 ± 205.36 ηg/ml) and the value obtained
one hour after exercise (534.77 ± 102.3 ηg/ml) t(7) =
3.10, p ≤ .01. Statistically significant differences also
occurred in LV3s, between post-exercise value (476.43 ±
197.82 ηg/ml) and the mean rest value (573.42 ± 169.76
ηg/ml) t(7) = 3.69, p ≤ .01. Therefore, we reject the null
hypothesis that there is no difference in concentration
of the IGF-1 between values at rest and post-exercise
in LV3s, as well as between rest and after one hour of
recovery in MV6s (Figure 3).
For C, only the MV6 trial yielded significant dif-
ferences between the concentrations at rest (673.76 ±
251.32 ηmol/l) and after one hour of recovery (320.28
± 114.17 ηmol/l) t(7) = 6.89, p ≤ .01, as well as post-
exercise (479.54 ± 218.24 ηmol/l) t(7) = 4.17, p ≤ .01.
Therefore, we reject the null hypothesis that there is
no difference in concentration of the cortisol between
training volume at every time point (Figure 4).
DISCUSSION
The main finding of this study is that the different
training volume (LV3, MV6, HV12) with constant
movement tempo in resistance exercise doesn’t impact
on post-exercise concentrations of T, only MV6 and
HV12 can elicit anabolic GH post-exercise response,
and only HV6 can elicit post-exercise IGF-1 response
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Wilk et al: Response to barbell squat
Fig. 3. The average concentration of the IGF-1 at various levels of training volume.
**p<0.01.
Fig. 4. The average concentration of the cortisol at various levels of training volume.
**p<0.01.
with decreased post-exercise C level. Therefore, the
MV6 resulted in most efficient hormonal post-exercise
response in terms of post exercise recovery.
Despite our use of variable-volume of exercise (LV3,
MV6, HV12) in the present study, no significant differ-
ences in post-exercise plasma testosterone levels were
observed, contrary to previous findings (Crewther et
al. 2008). While Kraemer and Ratamess (2005) sug-
gested that strong increases in serum testosterone
levels occur in participants with a relatively high base-
line levels of this hormone, this was not confirmed by
the results of the present study. The absence of sig-
nificant differences between resting and post-exercise
values may have resulted from high initial resting tes-
tosterone levels in these young participants (mean age
24), extensive training experience (mean of 6 years),
and/or time of day of sampling (9 am). It is possible
that circadian rythym changes masked exercise-related
changes of in testosterone (Sedliak et al. 2007; Cook
and Crewther, 2012). It is also possible that the lack
of significant differences in post-exercise testosterone
levels could have been due to the length of rest periods
between sets (5 minutes), since Kraemer et al. (1991)
suggested that the length of rest periods between sets
determines the effective impact of strength training
on the elevation of testosterone levels and should not
exceed two minutes. Kraemer et al. (1991) also sug-
gested that exercise-induced changes in testosterone
may be influenced by the type of exercise performed.
While an increase in plasma testosterone levels was
observed when powerlifting exercises targeting sev-
eral muscle groups were performed at the same time
(Kraemer et al. 1991), the present study did not find
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Wilk et al: Response to barbell squat
this association with just one exercise being used (back
barbell squat), even at varying exercise volumes.
Strength training which results in a significant
increase in C levels generally involves a higher number
of repetitions than three and significantly shorter
rest intervals between sets than were performed in
the present study (Smilios et al. 2003). Our findings
suggest that a five-minute rest period between sets,
despite a large number of sets performed at 90% of the
1RM load, does not stimulate glycolysis significantly,
and thus does not result in a significant increase in
C levels. Research showed that when the resting con-
centration of C is high, no post-exercise elevation was
found (Beaven et al. 2008), and in some cases a post-
exercise decrease in concentrations of this hormone
was observed, compared to resting levels. This study
demonstrated a significant difference in cortisol con-
centrations only in the MV6 where exercise-induced
C levels were significantly lower than baseline values
prior to exercise.
The present study demonstrated that the volume of
12 sets (HV12) did not result in a greater GH secretion
in comparison to the LV3 and MV6. Thus, we suggest
that the unfavorable increase in C levels associated
with a higher volume indicates that the MV6 could be
more beneficial with respect to post-exercise endo-
crine adaptation. Previous research suggested that
when the optimal volume is exceeded, the GH peak
occurs already during the training session (Schwarz et
al. 1996; West el al., 2012). It is possible that this was
the case during the maximal volume protocol (HV12),
yet no measurements were performed between par-
ticular sets to confirm this hypothesis.
Analyses of changes in IGF-1 concentrations during
our different strength training protocols demonstrated
decreases in the LV3 and MV6 trials, and despite com-
parable training variables, the results we obtained were
contradictory to those reported in earlier research
(Kraemer et al. 1991). Some research results indicate
that when anabolic processes in the body are predomi-
nant, strength training stimulates the exercise-induced
elevation of IGF-1 concentrations, as demonstrated by
previous research Forbes et al. (1989). The results of
the present research, may be indicative of the predomi-
nance of catabolic environment in the subjects (with
exception of decreased C level in MV6), which could
partly explain the absence of exercise-induced increase
in IGF-1 levels. It is known that the metabolic state of
the body and the level of target cell sensitivity to the
released IGF-1 is the essential stimulating mechanism
for changes in IGF-1 concentrations (Ambrosio et al.
1996). In this study, a significant elevation of IGF-1
concentrations was not observed, and even decreased
significantly after the low volume training proto-
col (Figure 3). A significant decrease also occurred
between the concentrations measured prior to exercise
and after one hour of recovery, in the moderate train-
ing volume trial. Resting IGF-1 levels were high in this
study, what confirms a previous hypotheses that the
exercise-induced elevation of IGF-1 levels are more
likely to be observed when baseline concentrations
are low (Kraemer et al. 1991). The high resting con-
centration of IGF-1 may be associated with the effects
of nocturnal GH secretion (Ohlsson et al. 2009). The
measurement of resting IGF-1 concentration was per-
formed at approximately 9 am. Research showed that
the duration of IGF-1 secretion due to the influence
of GH can be approximately 12 hours long (Kraemer
& Ratamess, 2005), which may partly explain the high
resting IGF-1 concentrations.
A negative correlation between the concentrations of
cortisol and testosterone has been reported (Brownlee
et al. 2005). The study by Brownlee et al. (2005) also
show a positive correlation between concentrations of
cortisol and free testosterone. In addition to the effects
of testosterone, the important post-training role of GH
or IGF-1 should be taken into account. Anabolic hor-
mones were identified as having a significant impact on
muscle tissue remodelling (Viru & Viru, 2004). Hansen
et al. (2001) suggested that the adaptation is dependent
on the exercise-induced concentrations of anabolic hor-
mones, therefore optimizing the volume may be crucial
for maximal training effects. Research suggests that
the first hour of recovery is critical for the endocrine
response. After this period, the concentration of hor-
mones and growth factors generally returns to resting
levels (Tremblay et al. 2005; West et al. 2014) which was
confirmed by the present study but not in IGF-1 and
cortisol. The results of global research also indicate that
there are significant differences in individual hormonal
responses to specific types of exercise, (McGuigan et al.
2004; Beaven et al. 2008).
PRACTICAL APPLICATION
This study demonstrated that in terms of anabolic hor-
mone response, the most effective volume is close to
6 sets. It has been established that performing 12 sets
resulted in an increase of cortisol concentrations, while
6 sets led to a significant decrease in exercise-induced
cortisol levels compared to baseline. We believe it is rea-
sonable to suggest the volume of training which should
not be exceeded, since our data did not demonstrate
any favorable changes in hormone response with higher
volume training in experienced powerlifters.
CONCLUSIONS
This research indicates that among the many variables
of strength exercise, training volume and total training
load are the key factors stimulating the secretion of var-
ious hormones, both anabolic and catabolic. The con-
ducted study demonstrated that in terms of endocrine
response, the optimal volume of high intensity strength
exercise is about 6 sets in experienced powerlifters.
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Wilk et al: Response to barbell squat
ACKNOWLEDGEMENTS
This work was supported by the Charles University
UNCE/HUM/032.
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