Effects of different resistance training
frequencies on body composition and
muscular performance adaptations in men
, Abbas Asadi
, Paulo Gentil
, Pooria Jahangiri
, Adel Ghorbani
Anthony C. Hackney
and Hassane Zouhal
1Department of Exercise Physiology, Faculty of Sport Sciences, University of Guilan, Rasht,
2Department of Physical Education and Sport Sciences, Payame Noor University, Rasht, Guilan, Iran
3Faculdade de Educação Física e Dança, Universidade Federal de Goiás, Goias, Brazil
4Department of Physical Activity Sciences, Universidad de Los Lagos, Osorno, Chile
5Department of Exercise & Sport Science; Department of Nutrition, University of North Carolina,
Chapel Hill, North Carolina, United States
6M2S (Laboratoire Mouvement, Sport, Santé) –EA 1274, Univ Rennes, Rennes, France
7Centro de Investigación en Fisiología del Ejercicio, Facultad de Ciencias, Universidad Mayor,
Background: The aim of this study was to compare the effects of 8 weeks resistance
training (RT) with two sessions versus four sessions per week under volume
load-equated conditions on body composition, maximal strength, and explosive
actions performance in recreationally trained men.
Methods: Thirty-ﬁve healthy young men participated in the study and were
randomly divided into a two sessions per-week RT (RT2, n= 12), four sessions
per-week RT (RT4, n= 13) or a control group (CG, n= 10). All subjects were
evaluated for thigh, chest and arm circumference, countermovement jump (CMJ),
medicine ball throw (MBT), 1-repetition maximum (1RM) leg press, bench press,
arm curl, muscular endurance (i.e., 60% of 1RM to failure) for leg press, and bench
press at pre, mid (week 4) and post an 8-week training intervention.
Results: A two-way analysis of variance with repeated measures (3 [group] × 3
[time]) revealed that both training groups increased chest and thigh circumferences,
strength and explosive actions performance tests in comparison to CG following
8 weeks of training (p= 0.01 to 0.04). Group × time interactions were also noted in
1RM bench press (effects size [ES] = 1.07 vs. 0.89) and arm curl (ES = 1.15 vs. 0.89),
with greater gains for RT4 than RT2 (p= 0.03).
Conclusion: RT improved muscle strength, explosive actions performance and
markers of muscle size in recreationally trained men; however, four sessions of
resistance training per week produced greater gains in muscular strength for the
upper body measures (i.e., 1RM bench press and arm curl) when compared to two
sessions per week under volume-equated conditions.
Subjects Anthropology, Anatomy and Physiology, Clinical Trials, Kinesiology
Keywords Athletic performance, Body composition, Human physical conditioning, Recovery,
How to cite this article Arazi H, Asadi A, Gentil P, Ramírez-Campillo R, Jahangiri P, Ghorbani A, Hackney AC, Zouhal H. 2021. Effects of
different resistance training frequencies on body composition and muscular performance adaptations in men. PeerJ 9:e10537
Submitted 16 June 2020
Accepted 19 November 2020
Published 21 April 2021
Additional Information and
Declarations can be found on
2021 Arazi et al.
Creative Commons CC-BY 4.0
Resistance training (RT) is an exercise modality commonly used to improve muscle
hypertrophy and strength (ACSM, 2009;Fleck & Kraemer, 2004). Designing an optimum
RT program requires controlling variables such as the number of sets, repetitions,
intensity, exercise selection–sequence, and rest intervals (Fleck & Kraemer, 2004).
Recently, some studies have focused on the effects of RT frequency on muscular
adaptations (Arazi & Asadi, 2011;Dankel et al., 2017;Saric et al., 2018;Gentil et al., 2015).
The frequency of RT describe the number of training sessions performed per muscle
group in a given period (ACSM, 2009), which is commonly restricted to a week (Dankel
et al., 2017).
Previous studies have typically compared 1 vs. 2, 1 vs. 3, 3 vs. 4, and 3 vs. 6 times per
week RT frequencies on muscular adaptations, with controversial ﬁndings (Arazi & Asadi,
2011;Dankel et al., 2017;Saric et al., 2018;Gentil et al., 2015,2018;Brigatto et al.,
2018;Colquhoun et al., 2018;Gomes et al., 2018;Häkkinen & Kallinen, 1994;Raastad et al.,
2012;Zaroni et al., 2019;Schoenfeld et al., 2015;Yue et al., 2018). For example, when
Colquhoun et al. (2018) and Saric et al. (2018) compared 3 vs. 6 days per week RT on
muscular adaptations in resistance-trained men, with volume equated, both frequencies
induced similar gains in strength and muscle hypertrophy. In addition, Brigatto et al.
(2018) concluded that both one and two RT session per week promoted neuromuscular
adaptations including muscular strength and endurance with a similar change between
experimental conditions. Similarly, other authors reported similar changes in muscle
strength and hypertrophy with equal volume RT performed one or two times per week
in untrained (Gentil et al., 2015) and trained men (Gentil et al., 2018). In contrast, Zaroni
et al. (2019) examined well-trained men, with a split training routine with muscle
groups trained once per week vs. whole-body split training routine with muscle groups
trained 5 days per week, and found that higher frequencies induced superior hypertrophic
effect. Moreover, in a series of systematic review studies by Schoenfeld, Ogborn & Krieger
(2016) and Schoenfeld, Grgic & Krieger (2018) the authors addressed that twice weekly
RT in more effective than once a week RT to increase muscle hypertrophy.
The controversy between studies may derive from previous limitations among
published studies. For example, when RT programs of different frequency are performed
under volume-equated conditions, muscle strength gain is similar between different
frequencies (ACSM, 2009;Schoenfeld, Ogborn & Krieger, 2016;Schoenfeld, Grgic & Krieger,
2018). Another caveat in the literature is that comparisons are usually limited to muscle
strength and hypertrophy (Saric et al., 2018;Brigatto et al., 2018;Gomes et al., 2018;
Zaroni et al., 2019;Schoenfeld et al., 2015), and little is known about the effects of RT
frequencies on muscle power and endurance performance in recreationally trained
individuals. Moreover, randomized-controlled interventions, with an equated volume
load between different training frequencies are lacking. Therefore, the purpose of this
study was to investigate the effects of volume load-equated RT frequencies of 2 vs. 4 times
per week on muscular strength, endurance, power performances, and muscle size in
recreationally trained young men.
Arazi et al. (2021), PeerJ, DOI 10.7717/peerj.10537 2/16
In a randomized-controlled longitudinal design, subjects were divided into 3 groups,
including RT performed 2 times per week (RT2), 4 times per week (RT4) and a control
group (CG). The study duration lasted 12 weeks (Fig. 1). The main training intervention
period lasted 8 weeks and the subjects performed equal volume training with differing
training frequencies (i.e., 2 vs. 4 times per week). Pre, mid and post 8-week training,
one repetition maximum (1RM) of leg press, bench press, and arm curl, muscular
endurance (i.e., 60% of 1RM to failure) for the upper- and lower-body (i.e., bench press
and leg press), countermovement jump and medicine ball throw, in addition to thigh,
chest and arm circumferences were measured. Two measurements with 96 h apart were
used to determine the reliability of tests and the intraclass correlation coefﬁcient (ICC) of
all tests were r ≥0.95.
Thirty-ﬁve young men who recreationally trained RT (i.e., 2 or 3 days per week for at least
2 years) participated in this study. Inclusion criterions for the study were (1) no upper- and
lower-body injuries or orthopedic problems as screened by physician, (2) no medical
problems or any history of ankle, knee, or back pathology in the 3 months before the study,
(3) no lower or upper-body reconstructive surgery of any type in the past 2 years or
unresolved musculoskeletal disorders, (4) no problems of the cardiovascular and
endocrine systems. Furthermore, the subjects were required to not have used any
supplement or drug within the past 6 months prior to inclusion in this study which was
conﬁrmed by a personal interview. The subjects were assigned to 3 groups including:
2 times per week RT (RT2; n= 12, age = 19.8 ± 1.8 y, height = 1.75 ± 0.5 m, mass =
64.2 ± 5.7 kg, body fat = 16.6 ± 4.9%, and training age = 2.5 ± 0.5 y), 4 times per week RT
(RT4; n= 13, age = 19.9 ± 1.6 y, height = 1.77 ± 0.4 m, mass = 70.6 ± 8.2 kg, body fat =
18.0 ± 4.1%, and training age = 2.8 ± 0.7 y) and a control group (CG; n= 10, age =
20.4 ± 1.4 y, height = 1.78 ± 0.8 m, mass = 69.1 ± 8.0 kg, body fat = 18.4 ± 3.7%, and
training age = 2.3 ± 0.4 y) using computer-generated random numbers (Fig. 2). After being
informed about the study procedures, beneﬁts and possible risks, the participants signed
an informed consent form in accordance with the guidelines of the Institutional Review
Board at the University of Guilan (Project. 1398/2019).
1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. Weeks
Figure 1 Study design. Full-size
Arazi et al. (2021), PeerJ, DOI 10.7717/peerj.10537 3/16
The volunteers visited the laboratory 9 times for testing including 3 days for pre-test (24 h
apart between testing sessions), 3 days for mid-test (24 h apart between testing sessions),
and 3 days for post-test (24 h apart between testing sessions). The subjects were tested
at the same time of day (4 to 6 P.M.) and in the same order to minimize the effect of
circadian variations in the test results. All subjects were instructed to continue with their
normal daily life activities and dietary intake throughout the study duration.
Height was measured using a wall-mounted stadiometer (Seca 222, Terre Haute, IN, USA),
body mass was measured using a medical scale (BC-418MA; Tanita, Tokyo, Japan), and
skinfold thickness was measured at 3 sites (i.e., pectoral, quadriceps, and abdominal)
on the right side of the body using calipers (model 01128; Lafayette Caliper, Lafayette, IN,
USA) (Jackson & Pollock, 1985). Each site measurement was assessed 3 times and the
average of 3 trials was recorded for analysis. The circumferences of chest, mid-thigh, and
mid-arm on the right side of the body were assessed using tape measure with nearest
to 0.1 cm (Arazi, Damirchi & Asadi, 2013). The arm and thigh circumferences were
measured with the muscle maximally contracted. All anthropometric measures were
assessed by the same researcher who was experienced and qualiﬁed for the measurements.
Parcipants inclusion for the study
n = 40
n = 35
n = 12
n = 10
Removed based on
n = 5
n = 13
n = 12
n = 13
n = 10
n = 12
n = 13
n = 10
Figure 2 Study ﬂow. Full-size
Arazi et al. (2021), PeerJ, DOI 10.7717/peerj.10537 4/16
To avoid potential dietary confounding of results, 3-day diet recalls were completed at pre-
and mid study duration, and the subjects were advised to maintain their customary
nutritional regimen (i.e., approximately 25% protein, 25% fat and 50% carbohydrate) and
to avoid taking any supplements during the study period. The nutrition specialist
continued to meet with the subjects each week to assess adherence to their food and liquid
instructions and avoidance of drugs and ergogenic supplements using interview before the
initiation of each training session (Table 1).
Lower body muscular strength was assessed with the leg press exercise, upper-body
muscular strength was assessed using the free-weight barbell bench press and arm curl
exercises, respectively. The one repetition maximum (1RM) testing was performed
according to method previously described in detail (Arazi, Damirchi & Asadi, 2013;
Fleck & Kraemer, 2004). Brieﬂy, the subjects performed a warm-up set of 8 to 10
repetitions at a light weight (∼50% of 1RM). A second warm-up consisted a set of three to
ﬁve repetitions with a moderate weight (∼75% of 1RM), and third warm-up included
one to three repetitions with a heavy weight (∼90% of 1RM). After the warm-up, each
subject was tested for the 1RM by increasing the load during consecutive trials until the
subjects were unable to perform a proper lift, complete the range of motion, and/or
maintain correct technique. The 1RM test was determined by ∼5 sets of one repetition,
with 3–5 min of rest among attempts.
A bilateral leg press test was selected to provide data on maximal dynamic strength
through the full range of motion of the muscles involved. Bilateral leg press tests were
completed using standard a 45leg press machine (Nebula Fitness, Inc., Versailles, OH,
USA), with the subjects assuming a sitting position (about 120ﬂexion at the hips, 80
ﬂexion at the knees, and 10dorsiﬂexion) and the weight sliding obliquely at 45.
Table 1 Dietary intake assessed for the RT2, RT4 and control groups at pre and in the middle of the
training period (mean ± SD).
RT2 RT4 Control
Energy intake (kcal) Pre 2,632 ± 310 2,521 ± 276 2,618 ± 288
Mid 2,991 ± 298 2,892 ± 199 2,632 ± 299
Carbohydrate (g) Pre 270 ± 33 269 ± 39 272 ± 37
Mid 292 ± 41 298 ± 41 288 ± 33
Fat (g) Pre 85 ± 21 87 ± 23 81 ± 33
Mid 94 ± 24 92 ± 21 82 ± 38
Protein (g) Pre 108 ± 22 105 ± 21 100 ± 19
Mid 129 ± 26 125 ± 30 98 ± 22
Vitamin E (mg) Pre 9.6 ± 1.0 9.3 ± 1.2 9.1 ± 1.1
Mid 11.0 ± 1.5 10.7 ± 1.4 9.0 ± 0.8
Vitamin C (mg) Pre 72 ± 18 71 ± 17 70 ± 15
Mid 79 ± 21 78 ± 13 71 ± 18
Arazi et al. (2021), PeerJ, DOI 10.7717/peerj.10537 5/16
A manual goniometer (Q-TEC Electronic Co. Ltd., Gyeonggi-do, South Korea) was used at
the knee to standardize the range of motion. On command, the subjects performed a
concentric leg extension (as fast as possible) starting from the ﬂexed position (85) to reach
the full extension of 180against the resistance determined by the weight. The free-weight
barbell (DHZ Barbell Model, Tehran, Iran) bench press is a valid and speciﬁc method
to assess upper-body strength performance. This test initiated with the arms fully
extended, holding the weight directly above the chest. The weight is lowered at a controlled
speed and with a smooth motion, to just touch the chest then returned to the starting
position. The free-weight barbell (DHZ Barbell Model, Tehran, Iran) arm curl is used as a
valid method to assess hand muscle strength. This test initiated in standing position
holding barbell using two hands with the arms hanging by the side of body. The elbows
were in extending position and then the elbows are closed up to shoulder level while
contracting the biceps muscle. The spotters and an experienced strength and conditioning
coach provided verbal encouragement and ensure safety.
Before the endurance test, the subjects performed a short period of warm-up including
5 min of running and 5 min of stretching exercise and then performed 10 repetitions with
30–40% of 1RM for each exercise test. The muscular endurance tests were performed
according to method previously described in detail (Arazi, Asadi & Roohi, 2014). Brieﬂy,
after warm-up, the subjects performed as many repetitions as possible without stopping or
pausing between repetitions with 60% of 1RM to exhaustion with 1 h rest between the two
tests (i.e., bench press and leg press) (Arazi & Asadi, 2011).
Lower and upper body power performance
Lower body power performance was measured at ﬁrst, using the countermovement jump
test (CMJ). For the CMJ, subjects performed standard warm-up including 10 min light
running and ballistic movements and then performed ﬁve CMJs without arms akimbo
with 30-s rest period (Arazi, Asadi & Roohi, 2014). The Vertec (Muscle LabV718; Ergo
Jump Plus Bosco System, Langesund, Norway) was adjusted to match the height of the
individual participant by having him stand with the dominant side to the base of the
testing device. The dominant hand was raised and the Vertec was adjusted so that the
hand was the appropriate distance away from the marker based on markings on the device
itself. The subjects were instructed to ﬂex their knees until 90according to previously
established methods (Arazi, Asadi & Roohi, 2014). Each subject performed 3 maximal CMJ
with 30-s rest period and the greatest jump recorded for further analysis.
Upper body power performance was measured 30 min post CMJ test, using the
medicine ball throw (MBT). For the MBT, subjects performed standard warm-up
including 10 min of light stretching and ballistic movements for the upper body and then
performed ﬁve balls throwing with 30-s rest period. The subjects sat on the ﬂoor and ﬂexed
their elbow similar to basketball chest pass and push the ball (3 kg Rubber Medicine
Ball; Champion Sports, Taiwan) as far as possible. There was a ﬂoor-mounted tape
measure that was used to record distance from sitting position to ﬁrst contact of the ball.
Arazi et al. (2021), PeerJ, DOI 10.7717/peerj.10537 6/16
In fact, the distance of the throw of the medicine ball from sat position up to its ﬁrst
contact with the ground was measured as upper body power. Each subject performed ﬁve
maximal MBT with 30-s rest period (Abe et al., 2000) and the greatest distance recorded
for further analysis.
Resistance training program
Table 2 presented the summary of the RT program. The training protocol included a
mixture of single-joint and multi-joint exercises with equated training volume load
(repetitions × external load [kg]) between experimental groups. A 60 to 90 s period of rest
between sets and 2 to 3 min of rest between exercises were allowed. The RT intensity
was between 70% to 80% of 1RM which determined by 1RM testing prior to inclusion in
study schedule and weight was increased systematically if the prescribed amount of
repetitions were completed. Each training session was supervised by a researcher and
Certiﬁcated Strength and Conditioning Specialist, with a coach: trainee ratio of 1:5
(Gentil & Bottaro, 2013). To continuously provide appropriate loading based on the
current strength levels of the subjects, they tested at pre-training and after 4 weeks of
training to modify RT intensity.
A two-way analysis of variance with repeated measures (3 [group] × 3 [time]) was used
to determine signiﬁcant differences among groups. Assumptions of sphericity were
assessed using Mauchly’s test of sphericity, with any violations adjusted by use of the
Greenhouse-Geisser (GG) correction. When a signiﬁcant F value was achieved, Bonferroni
post hoc procedures were performed to identify the pairwise differences between the
Table 2 Resistance training protocol.
RT2 group Saturday Repetitions Tuesday Repetitions
Leg press 10-10-8-8 Leg extension 10-10-8-8
Lying leg curl 10-10-8-8 Deadlift 10-10-8-8
Lat pull down 10-10-8-8 Lat rowing 10-10-8-8
Bench press 10-10-8-8 Incline bench press 10-10-8-8
Lateral raises 10-10-8-8 Military press 10-10-8-8
Machine biceps curl 10-10-8-8 Arm curl 10-10-8-8
Machine triceps extension 10-10-8-8 Lying triceps extension 10-10-8-8
RT4 group Saturday and Tuesday Repetitions Sunday and Wednesday Repetitions
Leg press 10-8 Leg extension 10-8
Lying leg curl 10-8 Deadlift 10-8
Lat pull down 10-8 Lat rowing 10-8
Bench press 10-8 Incline bench press 10-8
Lateral raises 10-8 Military press 10-8
Machine biceps curl 10-8 Arm curl 10-8
Machine triceps extension 10-8 Lying triceps extension 10-8
RT2: 2 times per week resistance training, RT4: 4 times per week resistance training, RM: repetition maximum.
Arazi et al. (2021), PeerJ, DOI 10.7717/peerj.10537 7/16
means. Customized excel spread sheets were used to calculate all effect size (ES) statistics.
Hedge’s g (g = (Mpost –Mpre)/SDpooled) was utilized to calculate an effect size for all
measures. Threshold values for assessing magnitudes of ES were <0.2, trivial; 0.2–0.6,
small; 0.6–1.2, moderate; 1.2–2.0, large; 2.0–4.0, very large; and >4.0, nearly perfect
(Hopkins, Marshall & Batterham, 2009). The effect size is reported with the 95%
conﬁdence interval (CI) for all analysed measures. All data are presented as mean ± SD.
The ICC was used to determine the reliability of the measurements. The level of
signiﬁcance was set at p≤0.05. The statistical tests were performed using the SPSS
statistical package version 21 (Chicago, IL, USA).
The test–retest reliability coefﬁcient of all variable tests was r ≥0.95. At baseline, no
signiﬁcant differences were observed among groups in any dependent variables (p= 0.642).
In addition, the CG did not show signiﬁcant changes at any time point in the variables
There was no signiﬁcant difference between the RT2 (week 4 = 45.37 ± 5.62 kg, week
8 = 91.37 ± 11.51 kg) and RT4 (week 4 = 48.68 ± 6.77 kg, week 8 = 93.28 ± 12.42 kg) in the
training volume load at week 4 (p= 0.52) and week 8 (p= 0.46).
There were signiﬁcant time effects which indicated signiﬁcant increases in chest and
thigh circumferences at mid and post-training intervention for both the RT2 and RT4
(p= 0.01). No signiﬁcant increase was seen in the arm circumference for both the groups
(p= 0.6). There were signiﬁcant group by time interaction in chest (p= 0.018) and
thigh (p= 0.026) circumference increases following 8 weeks of training which indicated
signiﬁcant differences between trained groups than CG at mid and post-test values.
However, no signiﬁcant differences were observed between RT2 and RT4 in chest and
thigh circumferences at mid and post-test (Tables 3 and 4).
There were time effects which indicated signiﬁcant increases in 1RM of bench press, leg
press and arm curl at mid and post-training intervention for both the RT2 and RT4
(p= 0.001). There were group by time interaction in 1RM of bench press (p= 0.031)
and arm curl (p= 0.022) following 8 weeks of training which indicated statistically
signiﬁcant differences between the RT4 compared with RT2 at post-test. Compared with
CG, both the RT2 and RT4 groups indicated signiﬁcant differences at mid- and post-test
(p= 0.001) in all strength measures (Tables 3 and 4).
There was a time effect which indicated signiﬁcant increases in leg press endurance at
mid and post-training intervention for both the RT2 and RT4 (p= 0.001). There was a
signiﬁcant group by time interaction (p= 0.041) in leg press endurance which indicated
signiﬁcant increases between the trained groups than the CG at mid and post-test
values. However, no signiﬁcant differences were observed between RT2 and RT4 in leg
press endurance at mid and post-test (Tables 2 and 3). In bench press endurance,
there was a time effect which indicated signiﬁcant increases at mid and post-training
intervention for the RT4 (p= 0.001). There was a signiﬁcant group by time interaction
(p= 0.032) in bench press endurance which indicated signiﬁcant differences between the
RT4 than the CG at mid and post-test values (Tables 2 and 3). However, no signiﬁcant
Arazi et al. (2021), PeerJ, DOI 10.7717/peerj.10537 8/16
differences were observed between RT2 and RT4 in bench press endurance at mid and
post-test (Tables 2 and 3).
There were time effects which indicated signiﬁcant increases in CMJ and MBT at mid
and post-training intervention for both the RT2 and RT4 (p= 0.02). There were signiﬁcant
Table 3 Changes in anthropometric and performance variables in response to 8 weeks training intervention (mean ± SD).
Variable Group Testing time Statistics
Pre Mid Post
Chest circumference (cm) RT2 86.4 ± 4 88.7 ± 4.3*89.8 ± 4.5*
G = 0.08
RT4 86.5 ± 7.3 91.3 ± 8.6*
92.5 ± 8.1*
T = 0.001
CG 86.3 ± 6.8 87.1 ± 7.5 86.8 ± 7.2 G × T = 0.018
Thigh circumference (cm) RT2 53.6 ± 3.3 56.0 ± 3.7*
56.1 ± 3.4*
G = 0.54
RT4 54.7 ± 7.6 56.2 ± 6.0*
56.3 ± 6.3*
T = 0.001
CG 53.5 ± 4.4 52.1 ± 3.4 51.8 ± 4.2 G × T = 0.026
Arm circumference (cm) RT2 27.2 ± 2.5 28.2 ± 2.9 28.8 ± 2.5 G = 0.1
RT4 29.3 ± 3.4 29.8 ± 3.4 29.5 ± 3.1 T = 0.6
CG 27.6 ± 2.1 27.0 ± 1.2 26.6 ± 1.2 G × T = 0.12
1RM bench press (kg) RT2 63.5 ± 6.4 70.3 ± 7.3*
71.5 ± 10.5*
G = 0.12
RT4 64.6 ± 5.3 69.8 ± 10.6*
75.5 ± 12.8*
** T = 0.001
CG 64.4 ± 7.5 63.5 ± 7.5 64.8 ± 6.2 G × T = 0.031
1RM leg press (kg) RT2 201.2 ± 36.6 260.6 ± 48.0*
310.3 ± 52.5*
G = 0.48
RT4 203.4 ± 51.7 263.9 ± 68.5*
299.8 ± 64.2*
T = 0.01
CG 202.8 ± 45.2 204.1 ± 39.8 203.4 ± 41.2 G × T = 0.47
1RM arm curl (kg) RT2 28.7 ± 4.0 33.6 ± 4.0*
34.3 ± 8.2*
G = 0.1
RT4 28.6 ± 5.3 35.8 ± 6.2*
37.2 ± 8.7*
** T = 0.001
CG 29.1 ± 3.1 29.1 ± 2.5 29.9 ± 3.1 G × T = 0.022
Bench press endurance (repetitions) RT2 21.1 ± 3.6 21.5 ± 3.6 21.5 ± 3.8 G = 0.11
RT4 21.5 ± 2.6 23.0 ± 3.1*
23.5 ± 2.3*
T = 0.01
CG 19.4 ± 4.4 19.8 ± 4.6 20.1 ± 3.5 G × T = 0.032
Leg press endurance (repetitions) RT2 20.7 ± 7.0 24.1 ± 4.2*
26.5 ± 5.4*
G = 0.07
RT4 19.4 ± 4.8 27.0 ± 4.9*
27.2 ± 6.4*
T = 0.001
CG 20.2 ± 3.3 20.8 ± 5.5 19.3 ± 4.2 G × T = 0.041
Countermovement jump (cm) RT2 37.3 ± 4.4 41.7 ± 5.2*
43.7 ± 3.3*
G = 0.36
RT4 37.8 ± 4.6 41.6 ± 3.4*
42.8 ± 5.5*
T = 0.021
CG 37.4 ± 3.7 37.0 ± 3.9 37.1 ± 4.6 G × T = 0.047
Medicine ball throw (m) RT2 3.49 ± 0.52 3.64 ± 0.45*
3.72 ± 0.37*
G = 0.87
RT4 3.72 ± 0.5 3.86 ± 0.58*
3.99 ± 0.65*
T = 0.029
CG 3.49 ± 0.35 3.48 ± 0.4 3.49 ± 0.51 G × T = 0.048
Signiﬁcant differences compared to pre-value.
Signiﬁcant differences compared to mid-value.
Signiﬁcant differences compared to CG.
Signiﬁcant differences between training groups.
RT2: 2 times per week resistance training, RT4: 4 times per week resistance training, CG: control group.
G: group, T: time.
Arazi et al. (2021), PeerJ, DOI 10.7717/peerj.10537 9/16
group by time interaction (p= 0.04) in CMJ and MBT which indicated signiﬁcant
differences between the trained groups than the CG at mid and post-test values (Tables 2
and 3). However, no signiﬁcant differences were observed between the RT2 and RT4 in
CMJ and MBT at mid and post-test (Tables 3 and 4).
Table 4 Time point ES in anthropometric and performance variables in response to 8 weeks training intervention.
Variable Group ES (95% Cl)
Pre to mid Mid to post Pre to post
Chest circumference (cm) RT2 0.53 [−0.28 to 1.35]
0.24 [−0.56 to 1.04]
0.77 [−0.06 to 1.6]
RT4 0.58 [−0.2 to 1.37]
0.14 [−0.63 to 0.91]
0.75 [−0.04 to 1.55]
CG 0.11 [−0.77 to 0.98] −0.04 [−0.92 to 0.84] 0.07 [−0.81 to 0.95]
Thigh circumference (cm) RT2 0.66 [−0.13 to 1.45]
0.03 [−0.74 to 0.8]
0.72 [−0.07 to 1.52]
RT4 0.21 [−0.59 to 1.01]
0.02 [−0.78 to 0.82]
0.22 [−0.58 to 1.02]
CG −0.22 [−1.1 to 0.65] −0.08 [−0.95 to 0.8] −0.38 [−1.26 to 0.51]
Arm circumference (cm) RT2 0.36 [−0.42 to 1.13]
0.21 [−0.56 to 0.99]
0.62 [−0.17 to 1.41]
RT4 0.14 [−0.66 to 0.94]
0.09 [−0.71 to 0.89]
0.06 [−0.74 to 0.86]
CG −0.34 [−1.22 to 0.55] −0.32 [−1.2 to 0.56] −0.56 [−1.45 to 0.33]
1RM bench press (kg) RT2 0.96 [0−.15 to 1.77]
0.13 [−0.64 to 0.9]
0.89 [−0.08 to 1.7]
RT4 0.6 [−0.22 to 1.42]
0.47 [−0.34 to 1.28]
1.07 [−0.22 to 1.93]
CG −0.11 [−0.99 to 0.76] 0.18 [−0.7 to 1.06] 0.06 [−0.82 to 0.93]
1RM leg press (kg) RT2 1.35 [0.5 to 2.2]
0.96 [0.15 to 1.77]
2.33 [1.34 to 3.33]
RT4 0.96 [0.12 to 1.81]
0.52 [0.29 to 1.34]
1.6 [0.68 to 2.52]
CG 0.03 [−0.85 to 0.91] −0.02 [−0.89 to 0.86] 0.01 [−0.86 to 0.89]
1RM arm curl (kg) RT2 1.17 [0.22 to 2.12]
0.11 [−0.66 to 0.87]
0.84 [−0.04 to 1.64]
RT4 1.21 [0.34 to 2.08]
0.18 [−0.62 to 0.98]
1.15 [0.29 to 2.02]
CG 0.0 [−0.88 to 0.88] 0.27 [−0.61 to 1.15] 0.25 [−0.63 to 1.13]
Bench press endurance (repetitions) RT2 0.11 [−0.66 to 0.88]
0.0 [−0.77 to 0.77]
0.1 [−0.66 to 0.87]
RT4 0.51 [−0.31 to 1.32]
0.18 [−0.62 to 0.98]
0.79 [−0.04 to 1.62]
CG 0.09 [−0.79 to 0.96] 0.07 [−0.81 to 0.95] 0.17 [−0.71 to 1.05]
Leg press endurance (repetitions) RT2 0.57 [−0.21 to 1.35]
0.48 [−0.3 to 1.26]
0.9 [−0.09 to 1.71]
RT4 1.51 [0.61 to 2.42]
0.03 [−0.77 to 0.83]
1.33 [0.45 to 2.22]
CG 0.13 [−0.75 to 1] −0.29 [−1.17 to 0.59] −0.23 [−1.11 to 0.65]
Countermovement jump (cm) RT2 0.88 [0.08 to 1.69]
0.44 [−0.33 to 1.22]
1.59 [0.71 to 2.48]
RT4 0.91 [0.07 to 1.75]
0.25 [−0.55 to 1.06]
0.95 [0.11 to 1.8]
CG 0.1 [−0.78 to 0.98] 0.02 [−0.85 to 0.9] 0.07 [−0.81 to 0.95]
Medicine ball throw (m) RT2 0.3 [−0.47 to 1.07]
0.19 [−0.58 to 0.96]
0.49 [−0.29 to 1.27]
RT4 0.25 [−0.55 to 1.05]
0.2 [−0.6 to 1.01]
0.45 [−0.36 to 1.26]
CG 0.03 [−0.85 to 0.9] 0.0 [−0.88 to 0.88] 0.02 [−0.85 to 0.9]
Very large ES.
RT2: 2 times per week resistance training, RT4: 4 times per week resistance training, CG: control group.
Arazi et al. (2021), PeerJ, DOI 10.7717/peerj.10537 10/16
The aim of the present study was to examine the effects of an 8-week RT program
performed two or four times per week RT with equal weekly training volume on thigh,
arm, and chest circumferences, 1RM of back squat, bench press, and arm curl, muscular
endurance and explosive actions performance for the upper- and lower-body in
recreationally trained young men.
In circumference measures, both the training groups signiﬁcantly increased from
pre-to-post RT intervention in the chest and thigh circumferences, without signiﬁcant
change for the arm circumference. In addition, the gains in this marker of muscle size were
similar between the RT2 and RT4 groups (small to moderate ES, Table 3), with the
exception of pre-to-mid and pre- to-post, where the RT2 group that indicated moderate ES
while the RT4 group indicated small ES without statistically signiﬁcant differences.
The ﬁndings of the present study are in accordance with other studies that have reported
improvements in muscle size after RT with varied training frequencies (Arazi & Asadi,
2011;Saric et al., 2018;Colquhoun et al., 2018;Schoenfeld, Ogborn & Krieger, 2016;
Schoenfeld, Grgic & Krieger, 2018). In relation to the effects of training frequency on
changes in muscle size or muscular hypertrophy, Schoenfeld, Ogborn & Krieger (2016;
Schoenfeld, Grgic & Krieger, 2018) and Grgic, Schoenfeld & Latella (2018) reported
small (i.e., range between ES = 0.22 to 0.51) gains using different RT frequencies, while in
this study we found moderate (0.75 to 0.77 ES) gains in chest circumference after both
RT2 and RT4. Previous experimental studies reported that RT interventions with two
sessions per week induced small gains (i.e., 0.33 ES) but in this study we found moderate
(range between 0.62 to 0.77 ES) increases in arm, thigh and chest muscle size. This suggest
that RT with a frequency of at least 2 days per week is adequate to enhance muscle
size (Gentil et al., 2015;Colquhoun et al., 2018;Zaroni et al., 2019;Yue et al., 2018).
The RT2 group performed 4 sets per exercise in each training session, which may induce
stimulation of muscular hypertrophy, by signalling pathways that increase protein
synthesis and providing mechanical stress in the muscle ﬁbers (Fernandes et al., 2012
Padilha et al., 2019). However, it seems that the muscle hypertrophy expansion is more
impressed by volume of training and, considering that both groups trained at what has
been shown to be the optimal dose (Barbalho et al., 2019), it can be derived that frequency
of RT might play a subsidiary ﬁgure relevant to this and further investigations are needed
to illuminate the effects of training frequency under volume-equated conditions on
muscle size. In addition, whilst circumference measures has been shown to be reliable and
reproducible and might be an appropriate ﬁeld-centred criterion (De França et al.,
2015), to make careful deductions based on the evidence, subsequent studies should focus
on the use of direct gauges of muscle mass increase using MRI, DXA, ultrasound or
BIA; however, previous studies used the aforementioned equipment and reported small
gains in muscle hypertrophy using different training frequencies (Gentil et al., 2015,
Colquhoun et al., 2018;Zaroni et al., 2019;Yue et al., 2018;Schoenfeld, Ogborn & Krieger,
2016;Schoenfeld, Grgic & Krieger, 2018).
Arazi et al. (2021), PeerJ, DOI 10.7717/peerj.10537 11/16
Both RT groups increased their 1RM after 4 and 8 weeks training intervention. To date,
a large number of studies reported that RT is an optimum training modality for strength
enhancement in men and women (Abe et al., 2000;Arazi, Damirchi & Asadi, 2013;
Arazi, Asadi & Roohi, 2014). In relation to strength gains following the ﬁrst 4 weeks of
training, aside from muscular hypertrophy, neuromuscular changes may have taken place
(i.e., inter-muscular consonance ameliorations, augmented alpha motor-neurons ﬁring
rate, modiﬁed mechanical speciﬁcations of the muscle-tendon complex, ordonnance
and/or individual-ﬁber mechanics) (Loenneke et al., 2019).
The RT4 group gained signiﬁcantly greater strength than the RT2 in 1RM of bench
press and arm curl following 8 weeks of training. However, with comparing ES the RT2
indicated large and very large changes in 1RM of leg press following 4 and 8 weeks training
intervention. Grgic et al. (2018) in the review article addressed that muscular strength is
increased due to more training frequencies; however, RT frequency does not show
meaningful effect on muscular strength improvements while equated training volume.
They reported moderate ES for 2 and 4 times per week RT frequency (i.e., 0.83 and
1.08, respectively), whereas we found similar gains in bench press and arm curl but
large and very large ES in the 1RM leg press. The possible discrepancy in results could be
due to type of test measures such as multi-joint vs. single joint (i.e., leg press vs. knee
extension) and upper vs. lower body tests. Another possible mechanism for the greater
strength gains in bench press and arm curl 1RM after the RT4 compared to the RT2 could
be due to motor learning viewpoint. In fact, multi-joint motions including more mixed
RT exercises need to an accurate coordination and timing of muscle recruitment and a
greater grade of motor efﬁciency (Carroll, Riek & Carson, 2001). Therefore, increases in RT
frequency from 3 to 4 sessions per week would provide more exposure to a given test/
exercise, which can lead to a higher performance on that test (Mattocks et al., 2017) and
hence resulted in greater upper body strength gains in the RT4 group.
Our ﬁndings demonstrated signiﬁcant changes in lower and upper-extremity muscular
endurance for the RT2 and RT4 groups after 4 and 8 weeks training intervention. These
results are according to the last studies that displayed improvements in muscular
endurance following RT (Aagaard et al., 2002;Arazi, Damirchi & Asadi, 2013). When
comparing the ES, the RT4 showed more gains than RT2 in the endurance tests belonging
to leg press and bench press (Table 3). The possible explanation for these ﬁndings could be
due to the greater possibility of higher frequencies to enhance cellular adaptations
(i.e., mitochondrial biogenesis) to increase muscle endurance; however, the information
respective to this issue is rare and further studies are needed to explain the inﬂuence of
different RT frequencies on muscular endurance performance.
Both RT groups increased their upper- and-lower body power performance after 4 and
8 weeks training intervention. In line with the results of this study, previous studies
reported improvements in power performance after RT (Arazi & Asadi, 2011;Arazi,
Asadi & Roohi, 2014). Typically, increases in CMJ and MBT performance following ﬁrst
4 weeks of training and continually to 8 weeks training intervention could induced by
neuromuscular adaptations (Aagaard et al., 2002). In fact, an improvement in power
performance in the early stages of a strength training program is likely the result of
Arazi et al. (2021), PeerJ, DOI 10.7717/peerj.10537 12/16
adaptations in the nervous system (Assunção et al., 2016). In fact, Aagaard et al. (2002)
reported that the principal components of the training enforced progressions following
RT were elucidated by elevations in efferent neural drive. This may be one explanation
for the changes in lower- and upper-body power performance (i.e., CMJ and MBT)
after the RT intervention. However, this is the ﬁrst study that compared the effects of an
8 week RT with either 2 or 4 weekly training sessions on upper and lower-body power
performance. The distribution of training volume on either 2 or 4 weekly training sessions
yielded similar effects on power performance for stretch-shortening cycle tasks in CMJ and
MBT tests. The observed performance enhancements could be explained by inter-
muscular coordination improvements, increased alpha motor-neurons ﬁring rate,
improved mechanical characteristics of the muscle-tendon complex, improved muscle
size, architecture and/or single-ﬁber mechanics (Arazi & Asadi, 2011;Arazi, Asadi &
Roohi, 2014); however, more studies are needed to clarify the impact of training
frequencies on power related performance adaptation following RT.
RT improved muscle strength, power performance and markers of muscle size in
recreationally trained men; however, four sessions of resistance training per week
produced greater gains in muscular strength when compared to two session per week
under volume load-equated conditions. Two and four times per week RT induced
signiﬁcant effects on muscular adaptations following 8 weeks of training in recreationally
trained young men. In addition, RT for 4 times per week induced further adaptive
responses in muscular strength in bench press and arm curl. It can be recommended that
strength and conditioning professionals keep in their mind that 4 times a week RT could be
adequate for muscular strength gains and 2 times a week RT could be suitable for the
muscle size and power performance under volume load-equated conditions.
The authors are thankful to the participants of this study for their excellent collaborations.
ADDITIONAL INFORMATION AND DECLARATIONS
The authors received no funding for this work.
Rodrigo Ramirez Campillo is an Academic Editor for PeerJ.
Hamid Arazi conceived and designed the experiments, analyzed the data, authored or
reviewed drafts of the paper, and approved the ﬁnal draft.
Abbas Asadi conceived and designed the experiments, analyzed the data, prepared
ﬁgures and/or tables, authored or reviewed drafts of the paper, and approved the ﬁnal
Arazi et al. (2021), PeerJ, DOI 10.7717/peerj.10537 13/16
Paulo Gentil analyzed the data, authored or reviewed drafts of the paper, and approved
the ﬁnal draft.
Rodrigo Ramírez-Campillo analyzed the data, authored or reviewed drafts of the paper,
and approved the ﬁnal draft.
Pooria Jahangiri performed the experiments, prepared ﬁgures and/or tables, and
approved the ﬁnal draft.
Adel Ghorbani performed the experiments, prepared ﬁgures and/or tables, and
approved the ﬁnal draft.
Anthony C. Hackney analyzed the data, authored or reviewed drafts of the paper, and
approved the ﬁnal draft.
Hassane Zouhal analyzed the data, authored or reviewed drafts of the paper, and
approved the ﬁnal draft.
The following information was supplied relating to ethical approvals (i.e., approving body
and any reference numbers):
The Institutional Review Board at the University of Guilan approved this study
The following information was supplied regarding data availability:
The raw measurements are available in the Supplemental Files.
Supplemental information for this article can be found online at http://dx.doi.org/10.7717/
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