SHORT RESEARCH REPORT
INDIVIDUAL MUSCLE HYPERTROPHY AND STRENGTH
RESPONSES TO HIGH VS. LOW RESISTANCE TRAINING
FREQUENCIES
FELIPE DAMAS,1 CINTIA BARCELOS,1 SANMY R. NÓBREGA,1 CARLOS UGRINOWITSCH,2
MANOEL E. LIXANDRÃO,2 LUCAS M. E. D. SANTOS,1 MIGUEL S. CONCEIÇÃO,2 FELIPE C. VECHIN,2 AND
CLEITON A. LIBARDI1
1
MUSCULAB—Laboratory of Neuromuscular Adaptations to Resistance Training, Department of Physical Education,
Federal University of Sa˜o Carlos—UFSCar, Sa˜o Carlos, Sa˜o Paulo, Brazil; and 2School of Physical Education and Sport,
University of Sa˜o Paulo—USP, Sa˜o Paulo, Sa˜o Paulo, Brazil
ABSTRACT
Damas, F, Barcelos, C, Nóbrega, SR, Ugrinowitsch, C, Lixandrão, ME, Santos, LMEd, Conceição, MS, Vechin, FC, and
Libardi, CA. Individual muscle hypertrophy and strength responses to high vs. low resistance training frequencies. J
Strength Cond Res XX(X): 000–000, 2018—The aim of this
short communication was to compare the individual muscle
mass and strength gains with high (HF) vs. low (LF) resistance
training (RT) frequencies using data from our previous study.
We used a within-subject design in which 20 subjects had one
leg randomly assigned to HF (53 per week) and the other to
LF (2 or 33 per week). Muscle cross-sectional area and 1
repetition maximum were assessed at baseline and after 8
weeks of RT. HF showed a higher 8-week accumulated total
training volume (TTV) (p , 0.0001) compared with LF. Muscle
cross-sectional area and 1 repetition maximum values
increased significantly and similarly for HF and LF protocols
(p . 0.05). This short communication highlights that some
individuals showed greater muscle mass and strength gains
after HF (31.6 and 26.3% of individuals, respectively), other
had greater gains with LF (36.8 and 15.8% of individuals,
respectively), and even others showed similar responses
between HF and LF, regardless of the consequent higher or
lower TTV resulted from HF and LF, respectively. Importantly,
individual manipulation of RT frequency can improve the intrasubject responsiveness to training, but the effect is limited to
each individual’s capacity to respond to RT. Finally, individual
response to different frequencies and resulted TTV does not
necessarily agree between muscle hypertrophy and strength
gains.
Address correspondence to Dr. Cleiton A. Libardi, c.libardi@ufscar.br.
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2018 National Strength and Conditioning Association
KEY WORDS individual responsiveness, total training volume,
1 repetition maximum, muscle cross-sectional area
INTRODUCTION
R
esistance training (RT)-induced increases in muscle mass (i.e., hypertrophy) and strength have
significant impact in overall health, diseases prevention (29), and athletic performance (2). The
effect of RT weekly frequency on muscle hypertrophy and
strength development has been given special attention lately
(6,12,14,16,25,30). The rationale for examining the impact of
different frequencies on RT outcomes relies on recent studies
showing the time course of increases in muscle protein synthesis after RT session (lasting ;24–48 hours after an RT
session) (10,11,28). In addition, higher RT frequencies could
result in greater training volumes, which in turn would
positively affect muscle hypertrophy and strength gains
(16,26).
Notwithstanding, our group recently showed that
performing RT 2, 3, or 5 times per week resulted in
similar gains in muscle hypertrophy and strength after 8
weeks in untrained individuals, even with a higher 8-week
accumulated total training volume (TTV) for the higher
frequency (sets 3 reps 3 load) (3). Other reports also
showed similar RT outcomes after distinct RT frequencies
both in untrained and trained individuals, irrespectively of
matching TTV (4,6,8,14). However, these findings are not
universal, especially when higher training frequencies
result in greater TTV (16,25,30). These discrepancies
could be due, at least in part, to interindividual differences
in responsiveness to distinct RT frequencies. A large variability has been reported for muscle strength and hypertrophy outcomes even when subjects perform
standardized RT programs (1,9,20). However, no study
has evaluated the effects of manipulation of RT frequency
within the same individual.
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Individual Responses to Training Frequencies
The present short communication compared individual
muscle hypertrophy and strength gains with high (HF, 53
per week) vs. low (LF, 2 or 33 per week) RT frequencies in
the same subjects (unilateral design) over 8 weeks of RT
using data from our previous study (3). We hypothesized
that the intersubject variability would be high, but a perindividual analysis would show that most of the subjects
would respond better to the high RT frequency, as it results
in greater TTV over the training period.
METHODS
Experimental Approach to the Problem
This is a follow-up short communication to analyze individual responses to HF (RT performed 53 per week) and LF
(RT performed 2 or 33 per week) from our previous publication (3). In short, a within-subject approach was used in
which each subject performed RT after an HF with one leg
and an LF with the other leg. Subject’s legs were randomly
allocated in 1 of the 2 experimental protocols in a counterbalanced way. Specifically, one leg of each subject was allocated in the HF (10 dominant and 10 nondominant legs),
and the contralateral legs were then randomized in LF (10
dominant [5 in each low frequency, i.e., 2 or 33 per week]
and 10 nondominant legs [5 in each low frequency]). The
vastus lateralis muscle cross-sectional area (CSA) was assessed using ultrasound and the maximum dynamic strength
by a unilateral 1 repetition maximum (1RM) test, both
before and after 8 weeks of RT.
Subjects
The subjects included in this short communication were the
same from our previous article (3) (young untrained men,
mean 6 SD: n = 20,23 6 4 years [18-30 years old]; 174 6 6
cm; 72 6 8 kg). However, one participant was excluded from
the analyses because he did not complete the experiment
protocol because of personal reasons. The study was
approved by the Federal University of São Carlos Ethic
Committee, and each participant signed informed consent
before participation. All procedures performed in the study
were in accordance with the ethical standards of the institutional research committee and with the Helsinki declaration.
Procedures
Muscle Cross-Sectional Area and Maximal Dynamic Strength (1
Repetition Maximum). Vastus lateralis muscle CSA was
assessed using sequential images acquired by a B-mode
ultrasound with a 7.5-MHz linear probe (MySono U6;
Samsung, São Paulo, SP, Brazil) and an image-fitting technique that our group has validated previously (23). Maximal
dynamic strength was assessed using the 1RM test on the leg
extension machine following previously described criteria (7).
Resistance Training. All RT protocols were performed in a leg
extension machine (Effort NKR; Nakagym, Diadema, SP,
Brazil). Training protocol consisted of 3 sets of 9RM–12RM
to muscular failure. A 2-minute rest interval was allowed
2
the
between sets because it was showed to be sufficient to promote increases in muscle hypertrophy (15) and strength in
untrained individuals (17). Total training volume was calculated as sets 3 repetitions 3 load (kg).
Statistical Analyses
For the analyses, each leg (experimental unit) was grouped
into either an HF (legs previously allocated to the 53 per
week RT) or LF (legs previously allocated to 2 or 33 per
week RT) (3). For group analyses, the accumulated TTV and
changes in muscle CSA and 1RM values were compared
between HF and LF using paired t-tests. For individual analyses, if an individual that showed a difference in the response
(for CSA or 1RM increases) from HF or LF (or vice versa)
within 2 typical errors (CSA typical error = 1.38%, 1RM
typical error = 3.64%; values extracted from Ref. 3), no difference in the response between RT frequencies was considered. Relationships between variables were assessed using
the Pearson’s correlation. In addition, we defined an individual as “responder” to RT as one with a response greater than
2 typical errors from zero for increases in muscle CSA and
1RM; if not, he was considered as “nonresponder” (19). A
chi-square test was performed to compare the proportion of
individuals (responders) that had higher CSA and 1RM
gains (greater than 2 typical errors) after training between
HF and LF. In case of significant p values, standard residuals
were analyzed to determine which proportions were significantly different in the contingency table. Differences in the
estimated proportions were considered significantly different
if standard residuals were outside the interval [22, 2]. Significance was established as p # 0.05.
RESULTS
Total Training Volume, Changes in Muscle Cross-Sectional
Area, and 1 Repetition Maximum
Group analyses showed that HF resulted in higher 8-week
accumulated TTV (p , 0.0001) compared with LF
(Figure 1A). However, similar changes were found in CSA
and 1RM changes comparing legs that trained at HF vs. LF
(p . 0.05; Figure 1B, C, respectively).
The individual analyses showed that all subjects depicted
higher TTV for HF vs. LF (Figure 1A). For muscle hypertrophy, 6 individuals (31.6% of the sample) responded more
HF, 7 individuals (36.8% of the sample) responded more for
LF, and the other 6 individuals (31.6% of the sample)
showed no difference in the hypertrophic responses
between training frequencies (the difference was within 2
typical errors) (Figure 1B). Regarding muscle strength, 5
individuals (26.3% of the sample) increased more the 1RM
value for HF, 3 (15.8% of the sample) for LF, and the other
11 (57.9% of the sample) showed similar responses between
RT frequencies (Figure 1C). No significant correlations were
found between TTV and CSA (p = 0.59; r = 0.09) or 1RM
(p = 0.17; r = 0.22). Importantly, after manipulation of the
RT frequency (i.e., HF-to-LF or LF-to-HF), only one
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Figure 1. A) Individual 8-week accumulated total training volume (TTV, sets 3 reps 3 load [kg]), % changes in (B) muscle cross-sectional area (CSA) and (C) 1
repetition maximum (1RM) at week 8 relative to baseline for high and low resistance training frequencies. Pointed lines in panels (B) and (C) indicate “zero”
value, and dashed lines indicate “cut-points” for responsiveness: 2.76% for CSA and 7.28% for 1RM (see Methods for details). *Significant difference from
lower resistance training frequencies (p , 0.0001).
individual (marked as “white upside-down triangle”) was
still considered “nonresponder” for muscle hypertrophy.
For muscle strength, after RT frequency manipulation, no
individual was still considered a “nonresponder.” The chisquare test showed that there were no significant differences
between the proportion of individuals who become responders after HF or LF for both CSA and 1RM gains (p
. 0.05).
DISCUSSION
This is the first study to analyze individual responses to
different RT frequencies. As hypothesized, our results
showed a large intersubject variability to HF and LF, but
contrarily to what we proposed, most subjects did not show
greater responses (muscle hypertrophy and strength) to the
RT frequency that resulted in a larger TTV.
Our unilateral RT protocol elaborated to minimize
between-subject variability, allowed to compare the leg that
performed an HF (RT 53 per week) with the contralateral
leg, which performed an LF (RT 2 or 33 per week). In
accordance with our previous article (3), group analyses
showed higher TTV for HF (Figure 1A), but similar hypertrophic (Figure 1B) and muscle strength (Figure 1C) outcomes between HF and LF. An interesting hypothesis is that
there might exist a training volume threshold beyond which
there is no further increase in muscle mass and strength, as
discussed in more detail recently (13). In fact, the individual
analyses demonstrate that a significant proportion of subjects showed no difference in their responses manipulating
RT frequency (31.6% of the subjects for muscle hypertrophy
and 57.9% for muscle strength). Even so, some individuals
greatly increased the muscle CSA and 1RM values in
response to an HF, but, surprisingly, other responded better
to LF, despite all subjects had greater TTV after HF (Figure 1). Corroborating with the results above, when RT frequency is manipulated, we report no correlation between
TTV and CSA or 1RM increases. These results do not fully
support the hypothesis that the magnitude and duration of
elevated muscle protein synthesis in response to RT bout and
the greater accumulated TTV would favor training muscles
with a greater frequency. Specifically, for muscle hypertrophy,
;31.6% of the sample responded more for HF, and for muscle strength, ;26.3% of the sample benefited more from HF.
We suggest that some individuals might be “less sensitive” to
RT stimulus, requiring a higher RT frequency (or TTV) to
maximize their RT-induced adaptations. Some studies with
endurance training indicate that individuals considered as
low responders (e.g., have small or no increase in maximal
_ O2max]) may better respond to highoxygen consumption [V
er training volumes (18,27). The same concept does not seem
to hold for RT, as some subjects (36.8% for muscle hypertrophy and 15.8% for muscle strength) in this study were more
responsive to LF (and consequent smaller TTV). These results could indicate that these subjects might require a longer
time to recover between sessions or even that they are more
sensitive to inhibitory mechanisms of hypertrophy and
strength gains performing larger weekly TTV. These suggestions require further investigation. In addition, we expand the
TTV threshold hypothesis, indicating that should it really
exists, it is to some extent individual-dependent, and further
increases in TTV can even impair muscle mass and strength
development with RT in some individuals.
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Individual Responses to Training Frequencies
Interestingly, 3 subjects (of 19) were considered as
“nonresponders” for muscle hypertrophy considering HF
and LF separately, but only 1 subject was considered
a “nonresponder” after the manipulation of RT frequency
(HF-to-LF or LF-to-HF) (Figure 1B). For muscle strength,
also 3 subjects were considered as “nonresponders” after
HF or LF separately, but all were considered as “responders” when RT was manipulated (Figure 1C). However, it
should be highlighted that despite the manipulation of RT
frequency can alter intraindividual responsiveness to RT,
the interindividual responses are dependent on each individual’s genetic predisposition to respond to RT. Other
factors as nutritional patterns, daily activities, etc., could
also have an impact on intersubject responsivity to RT.
Our data show that some individuals presented greater
responses in comparison with other subjects irrespectively
of RT frequency, i.e., even the smallest increase that some
subjects achieved was still higher than the largest increase
of other. Overall, the individual manipulation of RT frequency is relevant because it can improve the intrasubject
responsiveness to training, but the effect is limited to each
individual capacity to respond to RT.
It should also be noted that the intrasubject muscle
hypertrophy and strength responses were not aligned
between RT frequencies, i.e., a given individual can show
a better hypertrophic response to HF, but increase more
muscle strength for LF (or vice versa, Figure 1). Our results
showed that only 6 of 19 subjects (;32% of our sample size)
showed an aligned response for muscle strength and hypertrophy after the same RT frequency (whether HF or LF).
This suggests that the biological mechanisms regulating individual responsivity to different RT frequencies regarding
muscle strength and mass gains are distinct. Future studies
should investigate the individual’s biological mechanisms
behind the effect of manipulations of RT variables, as it is
plausible to consider that not only frequency and TTV, but
also load, muscle actions, repetition duration, and rest, for
example, could modulate individual responsiveness to muscle hypertrophy and strength adaptations.
Importantly, the results of this study can be specific to
previously untrained young men performing RT for 8
weeks. Both sex and age could alter the effect of training
frequency because of differences in fatigability, time to
recover from training, and required RT weekly dose
(5,21,22). It is also possible that longer RT periods and
the use of previously trained subjects could modulate
the individual responses to distinct RT frequencies.
Trained individuals depict a shorter increase in muscle
protein synthesis (10), and longer training periods (e.g.,
6 months) was showed to result in a dosed response of
weekly training volume in muscle hypertrophy (24). Thus,
it is possible that trained individuals, in general, would
require more frequent training stimulus (and maybe higher weekly volumes), decreasing interindividual variability
as subjects become more trained. These speculations
4
the
require further scrutinization. In addition, the use of unilateral exercise was specifically chosen to evaluate the
intraindividual variability to distinct RT frequencies performed during the same time frame (i.e., 8 weeks), but
other research are commended to investigate this research
question using, e.g., bilateral exercises and a wash-out
period. Also, upper-body and additional exercises could
be tested, as maybe a different pattern of response could
emerge.
In conclusion, this short communication highlights that
interindividual variability to different RT frequency (and
consequent TTV) is high, and, surprisingly, some individuals
showed greater muscle hypertrophy and strength gains after
lower RT frequencies, which resulted in lower TTV.
Importantly, intrasubject responsiveness to training can be
modulated through the manipulation of RT frequency;
however, the effect is limited to each individual’s capacity
to respond to RT. Finally, the individual response to different
frequencies and resulted TTV does not necessarily agree
between distinct RT-related outcomes (i.e., muscle hypertrophy and strength gains).
PRACTICAL APPLICATIONS
Considering individual responses, some subjects respond
better after a higher RT weekly frequency and consequent
accumulated RT volume, others might benefit more from
lower RT weekly frequencies and accumulated RT volume,
and even others show similar responses irrespective of RT
frequency manipulation. Importantly, this occurred despite
the fact that previously untrained subjects were studied in
the present investigation, challenging the notion (based on
average group values) that any training scheme maximally
stimulates RT-related outcomes in this population. In
addition, manipulation of RT frequency has an impact on
intrasubject responsiveness to training, but this effect is
limited to the each individual’s capacity to respond to RT.
Finally, care should be taken on which RT outcome (e.g.,
muscle hypertrophy or strength) should be the training
focus, as individual responsiveness to different RT outcomes
may differ among RT frequencies and volumes chosen.
ACKNOWLEDGMENTS
This work was supported by the São Paulo Research Foundation (FAPESP) (#2016/24259-1 to F.D., #2016/22635-6
to M.E.L., and #2013/21218-4 and #2017/04299-1 to C.A.
L.) and the National Council for Scientific and Technological
Development (CNPq) (#406609/2015-2 to C.U.) grants.
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