Effects of equal-volume resistance training with different training frequencies in muscle size and strength in trained men

Abstract

Background
The objective of the present study was to compare the effects of equal-volume resistance training (RT) performed with different training frequencies on muscle size and strength in trained young men.

Methods
Sixteen men with at least one year of RT experience were divided into two groups, G1 and G2, that trained each muscle group once and twice a week, respectively, for 10 weeks. Elbow flexor muscle thickness (MT) was measured using a B-Mode ultrasound and concentric peak torque of elbow extensors and flexors were assessed by an isokinetic dynamometer.

Results
ANOVA did not reveal group by time interactions for any variable, indicating no difference between groups for the changes in MT or PT of elbow flexors and extensors. Notwithstanding, MT of elbow flexors increased significantly (3.1%, P < 0.05) only in G1. PT of elbow flexors and extensors did not increase significantly for any group.

Discussion
The present study suggest that there were no differences in the results promoted by equal-volume resistance training performed once or twice a week on upper body muscle strength in trained men. Only the group performing one session per week significantly increased the MT of their elbow flexors. However, with either once or twice a week training, adaptations appear largely minimal in previously trained males.

Full text

Submitted 14 February 2018
Accepted 30 May 2018
Published 22 June 2018
Corresponding author
Paulo Gentil,
paulogentil@hotmail.com
Academic editor
Rodrigo Ramírez-Campillo
Additional Information and
Declarations can be found on
page 8
DOI 10.7717/peerj.5020
Copyright
2018 Gentil et al.
Distributed under
Creative Commons CC-BY 4.0
OPEN ACCESS
Effects of equal-volume resistance
training with different training
frequencies in muscle size and strength
in trained men
Paulo Gentil1, James Fisher2, James Steele2, Mario H. Campos1,
Marcelo H. Silva1, Antonio Paoli3, Jurgen Giessing4and Martim Bottaro5
1College of Physical Education and Dance, Universidade Federal de Goiás, Goiania, GO, Brazil
2School of Sport, Health, and Social Sciences, University of Southampton, Southampton, United Kingdom
3Department of Biomedical Sciences, University of Padova, Padova, Italy
4Institute of Sport Science, Universität Koblenz-Landau, Landau, Germany
5Faculdade de Educa¸
cão Física, Universidade de Brasília, Brasilia, DF, Brazil
ABSTRACT
Background. The objective of the present study was to compare the effects of equal-
volume resistance training (RT) performed with different training frequencies on
muscle size and strength in trained young men.
Methods. Sixteen men with at least one year of RT experience were divided into two
groups, G1 and G2, that trained each muscle group once and twice a week, respectively,
for 10 weeks. Elbow flexor muscle thickness (MT) was measured using a B-Mode
ultrasound and concentric peak torque of elbow extensors and flexors were assessed
by an isokinetic dynamometer.
Results. ANOVA did not reveal group by time interactions for any variable, indicating
no difference between groups for the changes in MT or PT of elbow flexors and
extensors. Notwithstanding, MT of elbow flexors increased significantly (3.1%, P<
0.05) only in G1. PT of elbow flexors and extensors did not increase significantly for
any group.
Discussion. The present study suggest that there were no differences in the results
promoted by equal-volume resistance training performed once or twice a week on
upper body muscle strength in trained men. Only the group performing one session per
week significantly increased the MT of their elbow flexors. However, with either once
or twice a week training, adaptations appear largely minimal in previously trained males.
Subjects Kinesiology
Keywords Resistance training, Skeletal muscle, Lean muscle mass, Muscle adaptation
INTRODUCTION
Designing resistance training (RT) programs involves the manipulation of numerous
variables that interact with each other (e.g., number of sets, repetitions, rest intervals,
etc.), which can have a large influence on the program outcomes (Paoli, 2012;Gentil et
al., 2017a). Among them, training frequency has recently received increased attention
and some authors consider it one of the most effective strategies to progress a resistance
How to cite this article Gentil et al. (2018), Effects of equal-volume resistance training with different training frequencies in muscle size
and strength in trained men. PeerJ 6:e5020; DOI 10.7717/peerj.5020

training program (Dankel et al., 2017). Considering that lack of time is a common barrier to
exercise adoption (Trost et al., 2002), identifying the minimal frequency of RT to optimize
adaptation is of importance. In this regard, condensing exercise sessions into fewer days,
while still performing an equal volume, might be a promising strategy, since it would
reduce the number of days required and also reduce the total time spent, considering
the time necessary for preparation and transport. Though it is argued that it might be
beneficial to train with higher frequencies to continue to produce adaptations (Dankel et
al., 2017), this might be challenging for most participants. Thus it is important to evaluate
the effectiveness of lower-frequency training programs.
Confirming the feasibility of this strategy, previous studies have shown that performing
RT only once a week increased muscle size and strength in untrained people (Graves et
al., 1990;Carpenter et al., 1991;Gentil et al., 2015). However, little is known about the
benefits of performing RT at low training frequencies in the gains of muscle size and
strength in resistance-trained individuals. The American College of Sports Medicine
recommends that trained participants use a frequency of four to five days per week for the
purpose of increasing muscle size and strength (ACSM, 2009), although it is not clear if
this frequency is referring to the number of sessions performed or the number of times a
given muscle is trained per week. The recommendation of higher training frequencies for
trained people is supported by the results of meta-analyses which suggest that experienced
individuals might benefit from training a muscle group multiple times per week (Rhea
et al., 2003;Peterson, Rhea & Alvar, 2004;Schoenfeld, Ogborn & Krieger, 2016;Grgic et al.,
2018). However, previous studies in bodybuilders reported that they usually perform split
routines training each muscle group only once per week (Hackett, Johnson & Chow, 2013;
Gentil et al., 2017b).
Increases in muscle size may in fact plateau relatively early after initiation of a RT
intervention suggesting trained persons have limited capacity to further increase muscular
size (Counts et al., 2017). However, this may be due to the attenuated anabolic response to
RT in trained individuals, and Dankel et al. (2017) have recently argued that there may be
a benefit for trained persons to perform greater frequencies of training. Given that there
is an increased difficulty in achieving significant results in trained individuals in response
to a RT stimulus, as evidenced through attenuated muscle protein synthesis (MPS), higher
training frequencies might allow for more frequent MPS rises and thus a greater MPS
area under the curve (Dankel et al., 2017). However, there is presently a lack of studies
testing this idea. We are aware of only two studies comparing the gains in muscle size and
strength between different training frequencies in trained participants (McLester, Bishop &
Guilliams, 2000;Schoenfeld et al., 2015) and the results are conflicting.
When analyzing experienced weightlifters, McLester, Bishop & Guilliams (2000),
concluded that three days per week of equal-volume resistance training was superior
to one day per week for bringing about strength gains. However, it is important to note
that the group that trained once per week were apparently stronger at baseline, which
may have influenced the comparisons. Moreover, the use of indirect measures to evaluate
changes in body composition (skinfolds and circumferences) may have limited the capacity
for evaluating muscle hypertrophy. Later, Schoenfeld et al. (2015) compared the effects of
Gentil et al. (2018), PeerJ, DOI 10.7717/peerj.5020 2/12

performing one or three sessions per muscle group per week in resistance trained men.
According to the results, higher frequency resulted in greater increases in the MT of elbow
flexors; however, no differences were observed for elbow extensor or vastus lateralis muscle
thickness. Similarly, statistically significant differences between groups were not noted for
1RM bench press and back squat.
If trained individuals can obtain similar results with lower training frequencies, this
could be a valuable strategy for prescribing RT programs for people with time constraints.
Therefore, the information provided by the present study would be valuable for conserving
training time and encourage participation whilst optimizing adaptation, as well as adding
to the existing body of knowledge on training variables. With this in mind, the purpose
of this study was to compare the effects of training one or two times per week on strength
and muscle size in trained college-aged men, while holding the total number of sets per
week constant. The hypothesis of the study is that training one or two days per week would
result in similar gains in muscle size and strength.
METHODS
Experimental approach to the problem
The participants were pair matched by baseline elbow flexor peak torque (PT) and then
randomly assigned into one of two groups: Group 1 (G1, n=8) trained upper body once
a week and Group 2 (G2, n=8) trained twice a week. G1 and G2 performed the same
exercises, with the same number of sets per week. All exercises were performed with three
sets of eight to 12 repetitions performed to momentary concentric failure as previously
defined (Steele et al., 2017). Before and after the 10 week training period, participants were
evaluated for elbow flexor MT and elbow extensor and flexor PT.
Subjects
Twenty male college students volunteered to participate in the study. Volunteers were
invited among those engaged in resistance training classes at the University. This sample
size was justified by a priori power analysis based on previous work by Schoenfeld et al.
(2015) with a target effect size difference of 0.6, alpha of 0.05 and power of 0.80. The
criteria for entering the study included being at least 18 years old, having at least 12
months of previous RT experience and having been practicing RT with direct supervision
uninterruptedly for the previous six months, and being free of health problems that could
prevent the participation in the study. To be included in the analyses, subjects had to
attend at least 80% of the training sessions (Gentil & Bottaro, 2013). The volunteers were
instructed to not change their nutritional habits during the study period, all of them
verbally confirmed that they maintained their diet throughout the trial period and no
relevant change was reported (i.e., becoming a vegetarian, restricting calories, taking
nutritional supplements or ergogenic aids, etc.). At the end of the study, 16 subjects met
the criteria for entering the analysis (22.3 ±2.0 years; 177.5 ±5.1 cm; 80.0 ±12.4 kg).
The exclusions (two in each group) were due to engagement in RT sessions other than the
study protocol, changes in nutritional habits (one participant became vegetarian) and/or
low training attendance (three participants). All participants had a history of training each
Gentil et al. (2018), PeerJ, DOI 10.7717/peerj.5020 3/12

muscle group two to three times per week, and all of them have been training each muscle
group two times a week in the previous four months.
The volunteers were notified of the research procedures, requirements, benefits and risks
before providing written informed consent. The Institutional Research Ethics Committee
granted approval for the study (56907716.5.0000.5083) and the study was performed
according to the Declaration of Helsinki.
Muscle thickness
Muscle thickness (MT) of the elbow flexors was measured before and after the 10-week
training period using B-Mode ultrasound (Philips-VMI, Ultra Vision Flip, model BF,
Amsterdam, Netherlands). The tests were conducted three to five days after the last
training session to prevent any swelling from influence measurement. During this time,
participants were oriented not to participate in any other exercise sessions or intense
activity. All tests were conducted at the right arm, at the same time of the day and the
participants were oriented to hydrate normally 24 h before the tests. MT of the elbow
flexors was measured according to Bemben’s procedures (Bemben, 2002) and was taken
as the distance from the subcutaneous adipose tissue-muscle interface to muscle-bone
interface (Abe et al., 2000). A trained technician performed all analyses. Baseline test and
retest intraclass correlation coefficient (ICC) for MT of elbow flexors was 0.95.
Isokinetic peak torque
Unilateral elbow flexion and extension isokinetic peak torque (PT) were tested on a Biodex
System 3 isokinetic dynamometer (Biodex Medical, Inc., Shirley, NY, USA). Tests were
performed at the dominant side with two sets of four concentric contractions at 60◦s−1
and 60 s rest between sets. The dynamometer was calibrated prior to each testing session
according to manufacturer specifications. Participants were seated on a Scott Bench and the
lateral epicondyle of the humerus was used to align elbow rotation to the dynamometer’s
lever arm. Volunteers were instructed to perform maximal efforts in all tests, and verbal
encouragement was constantly provided by the researchers. During elbow flexion, the
forearm remained in a supinated position throughout the test. For elbow extensions, the
forearm remained in a neutral position. Baseline test and retest ICC for peak torque were
0.96 for both elbow flexion and extension.
Resistance training intervention
Participants were divided into two groups. G1 (n=8) trained once a week (Mondays) and
G2 (n=8) trained twice a week (Mondays and Thursdays), and their characteristics are
presented in Table 1. The participants were allocated into groups in a counterbalanced
manner according to their values of elbow flexor PT. Both groups performed the same
exercises, with equal number of sets and repetition ranges; therefore, the only difference
was that G1 trained each muscle group once per week and G2 trained twice. The following
exercises were performed: lat pull down, seated row, barbell bench press, seated chest press,
standing barbell biceps curl, Scott bench biceps curl, lying barbell triceps extension and
high pulley triceps extension. All exercises were performed with three sets of eight to 12
repetitions to momentary concentric failure (Steele et al., 2017), and were provided with
Gentil et al. (2018), PeerJ, DOI 10.7717/peerj.5020 4/12

Table 1 Training sessions for Groups 1 and 2.
Monday Thursday
Group 1 Lat pull down
Seated row
Standing barbell biceps curl
Scott bench biceps curls
Barbell bench press
Seated chest press
Lying barbell triceps extensions
High pulley triceps extension
xxxx
Group 2 Lat pull down Seated row
Standing barbell biceps curl Scott bench biceps curls
Barbell bench press Seated chest press
Lying barbell triceps extensions High pulley triceps extension
verbal encouragement to maximize intensity of effort. If necessary, loads were adjusted
from set to set and between sessions to maintain performance of the desired number of
repetitions. All training sessions were closely monitored to ensure effort, repetitions and
intensity established by experienced strength and conditioning coaches, since previous
research has demonstrated greater gains in supervised vs. unsupervised training sessions
(Gentil & Bottaro, 2010). Rest interval between sets and exercises was maintained at
2 minutes.
Statistical analysis
Normality of the data was confirmed using the Kolmogorov–Smirnov test. Data are
presented as mean ±standard deviation. Groups were compared using factorial mixed
model ANOVA 2 ×2 (Group ×Time). When necessary, multiple comparisons with
confidence adjustment by the Bonferroni procedure were used for post hoc analysis. Data
were considered significant at P<0.05. Within groups, effect size (ES) was calculated
using Cohen’s d(threshold values were 0.2 for small, 0.5 for moderate and 0.8 for large).
Statistical analyses were performed using the Statistical Package for the Social Sciences 17.0
software (SPSS, Chicago, IL, USA).
RESULTS
Table 2 presents the characteristics of the participants and Table 3 presents the peak torque
values. The results for elbow flexor muscle thickness are presented in Fig. 1. There was
no significant difference in baseline values for age, height and body mass between G1 and
G2. The results of ANOVA did not reveal group by time interactions for any variable,
indicating no difference between groups for the changes in any of the muscle size and
strength variables. Elbow flexor and elbow extensor PT did not increase significantly for
any group. Elbow flexor MT increased significantly only for G1 (3.1% P<0.05).
Gentil et al. (2018), PeerJ, DOI 10.7717/peerj.5020 5/12

Figure 1 Changes in muscle thickness of elbow flexors. Individual values for pre- and post-training
muscle thickness of elbow flexors (mm). Group 1 trained each muscle group once a week and Group
2 trained each muscle group twice per week. * significant difference between pre- and post-values
(p<0.05).
Full-size DOI: 10.7717/peerj.5020/fig-1
Table 2 Characteristics of the participants in each group (mean ±standard deviation).
Group 1 Group 2
Age (years) 21.7 ±2.1 22.8 ±2
Weight (kg) 78.3 ±14 81.7 ±11.3
Height (cm) 176 ±4.9 178.9 ±5.2
Resistance training experience (months) 14.4 ±4.4 16.8 ±8.8
Table 3 Pre and post values for peak torque of elbow flexors and extensors, expressed as mean ±standard deviation.
Group 1 Group 2
Pre Post Delta ES Pre Post Delta ES
Elbow flexors’ peak torque (N.m) 66.6 ±12.1 66 ±11.6 −0.9% −0.03 66.7 ±13.9 67.1 ±12.7 0.6% 0.02
Elbow extensors’ peak torque (N.m) 57.7 ±10.2 57.6 ±5.7 −0.1% −0.01 55.4 ±13.1 55.8 ±11.7 0.9% 0.02
DISCUSSION
The results of our study showed that there were no differences in performing RT one or
two times a week with equal number of sets in trained men. Nonetheless, only the group
that trained once per week significantly increased muscle thickness. This is similar to a
previous study from our group using a similar training program in untrained participants
where there were no differences between groups for increases in muscle strength and size;
however, it is important to note that the effect sizes of muscle strength were higher in the
group that performed two sessions per week (Gentil et al., 2015).
Gentil et al. (2018), PeerJ, DOI 10.7717/peerj.5020 6/12

The results of the present study seem to contradict the results of previous studies
in trained men. When analyzing experienced weightlifters, McLester, Bishop & Guilliams
(2000) concluded that three days per week of equal-volume resistance training was superior
to one day per week for strength gains, suggesting that higher frequency of training may
be superior for trained individuals. However, as previously noted, the group that trained
at higher frequencies had lower strength levels at baseline. Considering that higher initial
values may be related to limited strength increases, this may have influenced the results.
More recently, Schoenfeld et al. (2015) compared the effects of exercising each muscle one
or three days per week in trained young men and suggested that increased frequency would
be beneficial for muscle strength and size. However, the authors highlighted that 16 of the
19 subjects reported training with a split routine on a regular basis, therefore, the novelty
factor of changing programs might have influenced results.
Interestingly, all participants of the present study have been training at higher frequencies
(exactly the same protocol performed by G1) for at least four months before the study and
only those that decreased frequency showed increases in muscle size. For this reason, we
cannot rule out that any positive adaptations were due to a variation in training stimuli
and not a benefit of reduced frequency per se. This might suggest that changing the usual
stimuli may be necessary to bring continued adaptations.
The lack of results in most variables seen in the present study is not surprising. Once
an individual is used to a given stimulus, there is a decline in training response, and a
plateau occurs far earlier than generally expected (Counts et al., 2017). Previous studies
demonstrated that muscle hypertrophy and strength gains in response to resistance training
seem to progressively diminish after a few weeks of training (Correa et al., 2013;Nader et
al., 2014) and comparisons of muscle size and strength gains between untrained and trained
participants showed a reduced response in the latter (Ahtiainen et al., 2003). In order to
overcome this plateau, it seems necessary to provide novel stimuli which is usually done
by changing load, repetition range and the exercises performed; the results of our study
might indicate that changing training frequency may be an effective strategy as well.
Considering that protein synthesis may return to basal levels in a few days after the
training session (Chesley et al., 1992;MacDougall et al., 1995;Burd et al., 2012), it has been
suggested that higher training frequency may promote a more favorable anabolic balance,
increasing long-term results (Dankel et al., 2017) Nevertheless, this was not observed
in the present study. In fact, recent studies showed that trained men did not recover
neuromuscular capacity four days after a high volume resistance training session (Ferreira
et al., 2017b;Ferreira et al., 2017a), suggesting that longer intervals between sessions might
be necessary when training with higher numbers of sets (>eight sets per muscle group).
Although it is commonly suggested that training must be repeated after two to three days
(ACSM, 2009), there are studies reporting positive results in trained men training once a
week (Ostrowski et al., 1997) and this approach has been widely used by bodybuilders using
split programs (Hackett, Johnson & Chow, 2013).
As lack of time is the most frequently cited barrier to exercise adoption (Trost et al.,
2002) using an exercise program that can be performed only once a week may improve
adherence in periods where time constraint might be an obstacle to continue training.
Gentil et al. (2018), PeerJ, DOI 10.7717/peerj.5020 7/12

Moreover, coaches and athletes might consider including variations in training frequency
in their training programs in order to overcome plateaus in muscle hypertrophy. In order
to gain further insight into time efficiency it would be of interest to test the effectiveness
of low training frequency with a low number of sets, which could be compensated by
increased intensity of effort. This was successfully employed in older people (Fisher et
al., 2014;Barbalho et al., 2017), but we are not aware of similar studies in young trained
participants.
This study is not without limitations. First, although the duration of the study was
similar to previous studies, 10 weeks may have not been long enough to allow us to find
statistical differences both within and between groups. In addition, the small sample size
might have affected statistical power. Despite this limitation, the inter-individual variability
was not high, except for elbow extensor PT, and analysis of effect sizes provides a good
basis for inferring that the results would not be clinically meaningful. Lastly, as Dankel et
al. (2017) note, there is a lack of studies examining frequencies higher than three times a
week. It remains a possibility that the lack of change in many outcomes for the present
study was due to both groups using relatively low frequencies (≤twice a week). Therefore,
future research should look to compare both lower (≤twice a week) to higher frequencies
(>three days a week).
The study did not have a non-training control group because our purpose was to compare
different training frequencies. However, since the study involved trained people that are
used to both the training and testing procedures, learning is not expected to influence
performance of the tests. It is also important to note that, whilst training frequency
changed for each situation, the total training volume was kept constant for both groups;
therefore, the duration of the session was longer for the group that trained only one time
per week. This should be taken in account, since the increased time demand at a specific
session might be a barrier for some people.
CONCLUSION
Trained men that are used to training at higher frequencies could benefit from decreasing
training frequency when pursuing muscle hypertrophy. Considering that the results seem
to be related to an unaccustomed stimulus, coaches and athletes might consider including
variations in training frequency, while keeping the number of weekly sets constant, in
their training programs in order to overcome plateaus in muscle hypertrophy. Moreover,
reducing training frequency may also be an efficient strategy to reduce time commitment
without interfering with the results.
ADDITIONAL INFORMATION AND DECLARATIONS
Funding
The authors received no funding for this work.
Competing Interests
The authors declare there are no competing interests.
Gentil et al. (2018), PeerJ, DOI 10.7717/peerj.5020 8/12

Author Contributions
•Paulo Gentil conceived and designed the experiments, performed the experiments,
analyzed the data, contributed reagents/materials/analysis tools, prepared figures and/or
tables, authored or reviewed drafts of the paper, approved the final draft.
•James Fisher, James Steele, Mario H. Campos, Marcelo H. Silva, Antonio Paoli and
Jurgen Giessing analyzed the data, authored or reviewed drafts of the paper, approved
the final draft.
•Martim Bottaro conceived and designed the experiments, performed the experiments,
analyzed the data, contributed reagents/materials/analysis tools, authored or reviewed
drafts of the paper, approved the final draft.
Human Ethics
The following information was supplied relating to ethical approvals (i.e., approving body
and any reference numbers):
The University of Goias granted Ethical approval to carry out the study within its
facilities (Ethical Application Ref: 56907716.5.0000.5083).
Data Availability
The following information was supplied regarding data availability:
The raw data are provided in Supplemental Information 1.
Supplemental Information
Supplemental information for this article can be found online at http://dx.doi.org/10.7717/
peerj.5020#supplemental-information.
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