Similar Muscular Adaptations in Resistance Training Performed Two Versus Three Days Per Week

Abstract

The purpose of the present study was to compare changes in muscle strength and hypertrophy between volume-equated resistance training (RT) performed 2 versus 3 times per week in trained men. Thirty-six resistance-trained men were randomly assigned to one of the two experimental groups: a split-body training routine (SPLIT) with muscle groups trained twice per week (n = 18) over four weekly sessions, or a total-body routine (TOTAL), with muscle groups being trained three times per week (n = 18) over three weekly sessions. The training intervention lasted 10 weeks. Testing was carried out pre- and post-study to assess maximal muscular strength in the back squat and bench press, and hypertrophic adaptations were assessed by measuring muscle thickness of the elbow flexors, elbow extensors, and quadriceps femoris. Twenty-eight subjects completed the study. Significant pre-to-post intervention increases in upper and lower-body muscular strength occurred in both groups with no significant between-group differences. Furthermore, significant pre-to-post intervention increases in muscle size of the elbow extensors and quadriceps femoris occurred in both groups with no significant between-group differences. No significant pre-to-post changes were observed for the muscle size of elbow flexors both in the SPLIT or TOTAL group. In conclusion, a training frequency of 2 versus 3 days per week produces similar increases in muscular adaptations in trained men over a 10-week training period. However, effect size differences favored SPLIT for all hypertrophy measures, indicating a potential benefit for training two versus three days a week when the goal is to maximize gains in muscle mass.

Full text

Journal of Human Kinetics volume 68/2019, 135-143 DOI: 10.2478/hukin-2019-0062 135
Strength & Power
1 - Department of Sport, School of Physical Education and Sport, University of São Paulo, São Paulo, SP, Brazil.
2 - Health Sciences Department, CUNY Lehman College, Bronx, NY, USA.
3 - Institute for Health and Sport (IHES)Victoria University, Melbourne, Australia.
Authors submitted their contribution to the article to the editorial board.
Accepted for printing in the Journal of Human Kinetics vol. 68/2019 in August 2019.
Similar Muscular Adaptations in Resistance Training Performed
Two Versus Three Days Per Week
by
Thiago Lasevicius1, Brad Jon Schoenfeld2, Jozo Grgic3, Gilberto Laurentino1,
Lucas Duarte Tavares1, Valmor Tricoli1
The purpose of the present study was to compare changes in muscle strength and hypertrophy between volume-
equated resistance training (RT) performed 2 versus 3 times per week in trained men. Thirty-six resistance-trained men
were randomly assigned to one of the two experimental groups: a split-body training routine (SPLIT) with muscle groups
trained twice per week (n = 18) over four weekly sessions, or a total-body routine (TOTAL), with muscle groups being
trained three times per week (n = 18) over three weekly sessions. The training intervention lasted 10 weeks. Testing was
carried out pre- and post-study to assess maximal muscular strength in the back squat and bench press, and hypertrophic
adaptations were assessed by measuring muscle thickness of the elbow flexors, elbow extensors, and quadriceps femoris.
Twenty-eight subjects completed the study. Significant pre-to-post intervention increases in upper and lower-body
muscular strength occurred in both groups with no significant between-group differences. Furthermore, significant pre-
to-post intervention increases in muscle size of the elbow extensors and quadriceps femoris occurred in both groups with
no significant between-group differences. No significant pre-to-post changes were observed for the muscle size of elbow
flexors both in the SPLIT or TOTAL group. In conclusion, a training frequency of 2 versus 3 days per week produces
similar increases in muscular adaptations in trained men over a 10-week training period. Nonetheless, effect size
differences favored SPLIT for all hypertrophy measures, indicating a potential benefit for training two versus three days
a week when the goal is to maximize gains in muscle mass.
Key words: frequency, strength training, hypertrophy, volume.
Introduction
The manipulation of resistance training (RT)
variables is thought to be paramount for
maximizing muscular adaptations in humans
(Kraemer and Ratamess, 2004). The American
College of Sports Medicine (2009) recommends
that resistance trained individuals should perform
a majority of repetitions with a load corresponding
to 6-12 repetition maximum (RM), using a
movement tempo of 1-2 seconds per muscle action
(i.e. concentric and eccentric phase), and taking 1 to
2 minutes rest between sets. Furthermore,
individuals should perform at least 10 sets per
week per muscle group to maximize muscular
adaptations (Schoenfeld et al., 2017). However,
research is somewhat limited as to the effects of
manipulating RT frequency. RT frequency can be
defined as the number of weekly RT sessions.
Frequency can also be characterized as how many
times a given muscle group is worked each week –
a definition that is more relevant to bodybuilders
and others seeking to maximize muscle growth
(Hackett et al., 2013).
The acute post-exercise muscle protein
synthesis (MPS) response to RT lasts ~48 hours in
untrained individuals (Phillips et al., 1997) and
there is evidence that this response is attenuated in
those acclimated to RT, whereby the time course is

136 Resistance training two vs. three days per week
Journal of Human Kinetics - volume 68/2019 http://www.johk.pl
reduced to ~36 hours or less (MacDougall et al.,
1995; Tang et al., 2008). Based on this attenuated
MPS response in trained individuals, some have
speculated that an increased RT frequency would
sustain elevations in MPS over time, thereby
maximizing the area under the curve and, in
theory, result in a greater muscle protein accretion
(Dankel et al., 2017). Consistent with motor
learning theory, it also can be surmised that
performing a given exercise more frequently over
time would elicit superior increases in strength,
conceivably through heightened improvements in
neural efficiency (Shea et al., 2000). However, the
hypothesis that greater RT frequencies enhance
muscular adaptations remains speculative. Such
inferences can only be gleaned from longitudinal
studies that directly compare different RT
frequencies while controlling all other variables.
A recent meta-analysis of longitudinal studies
on the topic of RT frequency found that training a
muscle group twice per week produced superior
gains in muscle mass as compared to a RT
frequency of once per week (Schoenfeld et al.,
2016). However, there were insufficient data to
determine whether even higher frequencies of
training would further enhance the hypertrophic
response. In addition, only two out of 10 studies
included in the meta-analysis involved resistance-
trained individuals, and both studies compared
training muscle groups once versus three times per
week (McLester et al., 2000; Schoenfeld et al., 2015).
Moreover, all of the studies that investigated
training frequencies of two versus three days per
week employed whole body measures of muscle
mass (e.g., dual-energy X-ray absorptiometry),
which are not as sensitive for detecting subtle
changes over time as site-specific measures such as
ultrasound or magnetic resonance imaging (Levine
et al., 2000; Maden-Wilkinson et al., 2013). It is
evident that there is a paucity of research
investigating the potential benefits of training
muscle groups at frequencies of two or more days
per week while using site-specific measures of
muscle growth and performed in those with
previous RT experience. Therefore, in an effort to
fill important gaps in the current literature, the
purpose of this paper was to compare changes in
muscular strength and hypertrophy between RT
performed two versus three days per week in a
group of resistance-trained men. In order to control
for potential confounding factors, the total weekly
RT volume (sets x repetitions x load) was equated
between groups as research shows that there is a
direct dose-response relationship between volume
and gains in both muscular strength and muscle
mass (Ralston et al., 2017; Schoenfeld et al., 2017).
Our hypothesis was that training muscle groups
three times per week would promote greater
muscular adaptations compared to a weekly
training frequency of twice per week.
Methods
Participants
The participants were 36 apparently healthy
male volunteers (age = 21.0 ± 3.0 yrs; body mass =
78.7 ± 9.8 kg; body height = 178.5 ± 6.0 cm; RT
experience = 3.2 ± 1.1 yrs); the sample size was
justified by a power analysis with the outcome
being vastus lateralis muscle thickness (MT) with
an effect size (ES) difference of 0.40, p = .05 and
power of 0.80 while factoring in the possibility of
six dropouts. Participants were considered to be
resistance-trained, defined as having a minimum
consistent RT experience of at least three days-per-
week (on most weeks) for one year. All participants
employed the bench press and squat exercises in
their usual training routines. Based on the baseline
strength and MT, the participants were pair-
matched and then randomly assigned to a split-
body routine (SPLIT) whereby muscle groups were
trained twice per week (n = 18) over four weekly
sessions, or a total-body routine (TOTAL), where
muscle groups were trained three times per week
(n = 18) over three weekly sessions. The University
of São Paulo Institutional Review Board approved
the research protocol, and all participants signed
an informed consent form.
Resistance training procedures
During the 10-week training period, the
participants were instructed not to do any
additional (i.e., external) RT. The specific protocols
for SPLIT and TOTAL routines are outlined in
Table 1. The number of repetitions per set was 8-
12, with sets carried out to the point of momentary
concentric muscular failure. The rest interval
between sets was 90 s. The cadence of repetitions
for concentric and eccentric actions was 2:2. All
training sessions were supervised by research
personnel experienced in RT performance. Before
the training program started, the participants were
tested for their 10 repetition maximum (RM) in all
of the exercises employed during the intervention.
The 10RM data were used to determine

by Thiago Lasevicius et al. 137
© Editorial Committee of Journal of Human Kinetics
participants’ initial training loads. During the
course of the study, we attempted to progressively
increase the external load by 2.5% when
participants performed more than 12 repetitions
for a given set of an exercise; alternatively, loads
were decreased by 2.5% when they performed
fewer than 8 repetitions for a given set of an
exercise.
Dietary adherence
The participants were advised to maintain
their usual and customary nutritional habits and to
avoid consuming any muscle-building
supplements during the study period. The
MyFitnessPal.com (http://www.myfitnesspal.com)
software was used for the collection of food
records. The food records were self-reported by the
participants twice: the first time was seven days
before the training program started and the second
time was in week ten of the intervention. The
participants were instructed by the research staff
on how to use the software and how to report their
food items. Total values of protein, carbohydrates,
and fats were recorded for further analysis.
Muscle thickness
B-mode ultrasound was used for the
assessment of MT (imaging unit: SonoAce R3,
Samsung-Medison, Gangwon-do, South Korea).
The assessment of MT was performed by an
experienced technician. Following the application
of water-soluble transmission gel (Aquasonic 100
Ultrasound Transmission gel, Parker Laboratories
Inc., Fairfield, NJ), the technician used a five MHz
ultrasound probe, which was placed
perpendicularly to the tissue interface with caution
been taken not to depress the skin. Upon obtaining
a satisfactory quality image, the image was saved
to hard drive. MT was measured according to the
protocol utilized by Abe et al. (2000).
Measurements were taken at two sites for the
upper-body (elbow flexors and elbow extensors)
and at two sites for the lower-body (rectus femoris
and vastus lateralis). For the upper-body,
assessment of MT was done at a site located 60%
distal between the humerus lateral epicondyle and
the acromion process of the scapula. For the lower-
body, the assessment was done at a site located
50% between the greater trochanter and the lateral
condyle of the femur. In order to reduce the
confounding impact of training-induced edema,
the assessment of MT was carried out 48-72 hours
after the final training session (Ogasawara et al.,
2012). The typical error (TE) and the coefficient of
variation for MT measurements of the elbow
flexor, elbow extensor, rectus femoris and vastus
lateralis were 0.8 mm (CV: 2.17%), 0.6 mm (CV:
2.13%), 1.0 mm (CV: 3.85%), and 1.0 mm (CV:
3.95%), respectively.
Muscle strength
Lower-body muscular strength was evaluated
using the 1RM Smith squat test (1RMSQUAT), while
upper-body muscular strength was assessed using
the 1RM barbell bench press test (1RMBENCH). For
testing at baseline and post-RT intervention, the
participants reported to the lab having refrained
from any exercise for at least 48 hours. Upon
arriving at the lab, the participants performed a
warm-up which consisted of light cardiovascular
exercise (~10 min). The first set of a given exercise
was carried out at a load of ~50% of the 1RM for
five repetitions. The second and third sets were
performed with two-three repetitions at a load
corresponding to ~60-80% of the 1RM. The
following sets were carried out with one repetition
while increasing weight for the 1RM determination
and resting from 3 to 5 minutes between each
successive attempt. All 1RM determinations were
made within 5 attempts. The participants’ thighs
were required to reach parallel in the 1RMSQUAT for
the attempt to be considered successful as
determined by the research assistants. Successful
1RMBENCH was achieved if the participant
displayed a 5-point body contact position (head,
upper back, and buttocks firmly on the bench with
both feet flat on the floor) and executed a full lock
out of the limbs. 1RMBENCH testing was conducted
first in the sequence; the 1RMSQUAT test was carried
out following a 5-min rest period. Hand and foot
placement during the muscular strength tests were
recorded at baseline, and the same positions were
reused for post-study performance.
The 10RM test was performed in the
following order: Smith squat, bench press, leg
press 45º, lat pulldown, leg extension, triceps
pushdown and biceps curl. The exercises were
selected because of their extensive use in RT
programs and ease of execution. Standardized
instructions were provided to participants prior to
the test. Final values were obtained within 3
attempts, with 3- to 5-min rest intervals afforded
between attempts. After obtaining the load in a
given exercise, recovery intervals of no less than 5
min were provided before proceeding to test 10RM

138 Resistance training two vs. three days per week
Journal of Human Kinetics - volume 68/2019 http://www.johk.pl
for the ensuing exercise.
10RM testing for the bench press and
Smith squat exercises followed the same
procedures as employed for the 1RM test.
Procedures for the other exercises were as follows:
1) Leg press 45º: the footplate of the unit
was divided into 10 x 10 cm squares with adhesive
tape to facilitate annotation of the feet positioning
on a sheet of paper and thus ensure reproducibility
in all testing sessions. Thereafter, the range of
motion for each repetition was determined by
having participants perform an unloaded
repetition, starting with the complete extension of
the knees up to 90º of flexion; a goniometer was
used to confirm the degree of flexion. A plastic
marker was then placed on the side column of the
leg press 45º to mark the knee flexion point. A
measuring tape was also glued onto the side
column of the apparatus to ensure reproducibility
of marker positioning.
2) Lat pulldown: participants sat on the
bench of the lat pulldown machine with the trunk
slightly inclined and knees semi-flexed. They
grasped the bar using a shoulder-width grip in full
elbow extension, and then pulled the bar down to
the chest by simultaneously adducting at the
shoulder joint and flexing at the elbow.
3) Leg extension: participants sat upright
with the trunk fully supported on the backrest of
extensor chair and knees at a 90º angle. Movement
was initiated by extending the knees until reaching
full extension and then flexing them back to the
initial position.
4) Triceps pushdown: participants
assumed a shoulder-width stance, knees semi-
flexed, elbows flexed at a 90º angle, and hands
holding the bar in a pronated position. Movement
entailed pushing down on the bar until achieving
complete elbow extension.
5) Biceps curl: participants assumed a
shoulder-width stance, knees semi-flexed, elbows
extended and hands holding the bar in a supinated
position. Movement entailed curling the bar until
achieving complete elbow flexion.
After obtaining the maximum loads in the
10RM test, participants rested for 48 hours and
were reevaluated to obtain the reproducibility of
the test (test and retest). The load established on
both days, a difference of less than 5% was
considered as the 10RM. In the intervals between
testing sessions, participants were instructed not to
perform any type of resistive exercise. The initial
loads used in the experimental conditions were the
highest obtained during pre-testing. The intraclass
correlation coefficients (ICC) for the tests were as
follows: Smith squat: ICC = 0.98; bench press: ICC
= 0.99; leg press 45º: ICC = 1.00; lat pulldown: ICC
= 0.99; leg extension: ICC = 0.99; triceps pushdown:
ICC = 0.97; biceps curl ICC = 0.99.
Statistical analysis
Initially, the data were analyzed
quantitatively and visually to verify their
normality (Shapiro-Wilk test) and existence of
outliers (box-plots). The TE of measurement was
used for measures of reliability, calculated as the
standard deviation of the difference between day
one and day two measurements / √2 and the
coefficient of variation calculated as the (TE of the
difference between day one and day two / means
of the day one and day two values) * 100. A one-
way ANOVA was performed to compare
differences between groups in the volume load and
dietary intake. A mixed model analysis was
performed for each dependent variable (MT and
1RM), with groups (TOTAL and SPLIT) and time
(pre- and post-intervention) as fixed factors, and
participants as a random factor. For each outcome,
an ES was calculated as proposed by Morris (2008).
The ES magnitude was classified as follows: <0.20
was considered as trivial, 0.20-0.50 was considered
as small, 0.50-0.80 as moderate and >0.80 was
considered as being of large magnitude (Cohen,
1988). Pre- to post RT intervention percent changes
were also calculated for the muscular strength and
hypertrophy outcomes ([post-testing value – pre-
testing value] / pre-testing value * 100). The
statistical significance threshold was set at p < .05.
All analyses were performed using the statistical
software package SAS 9.2 (SAS, NC).
Results
Eight participants dropped out over the
course of the study (four from each group). The
participants dropped out due to personal reasons
(non-related to the RT intervention). Thus, a total
of 28 participants completed the study (14 in each
group). Attendance was 95.6% and 95.3% for the
TOTAL and SPLIT group, respectively.
Dietary analyses
There were no significant differences in
average caloric intake or consumption of protein,
carbohydrate or fat between the TOTAL and SPLIT
groups. Data of daily dietary intake are presented

by Thiago Lasevicius et al. 139
© Editorial Committee of Journal of Human Kinetics
in Table 2.
Volume load
Volume load was calculated as sets x
repetitions x load for all sets performed during the
entire study. There were no differences in the
volume load between groups for chest (p = .89; 95%
confidence interval [CI] = -20912.0, 18363.5), back
(p = .79; 95% CI = -13364.7, 17270.9), elbow flexors
(p = .25; 95% CI = -2600.9, 9489.2), elbow extensors
(p = .74; 95% CI= -24719.9, 17869.2) and anterior
thigh (p = .78; 95% CI = -74560.3, 100729.0). Results
are presented in Table 3.
Muscle thickness
MT of the rectus femoris increased from
baseline to post-study by 7.9% (p < .001) and 12.3%
(p < .001) for TOTAL and SPLIT groups,
respectively, with no statistical differences noted
between groups (p = .50; CI = -0.19, 0.09; ES
difference = 0.39) (Table 4).
MT of the vastus lateralis increased from
baseline to post-study by 12.2% (p < .001) and 16.9%
(p < .001) for TOTAL and SPLIT groups,
respectively, with no statistical differences noted
between groups (p = .54; 95% CI = -0.25, 0.13; ES
difference = 0.31) (Table 4).
There were no statistical differences noted for
time or between groups in MT of the elbow flexors
(p = .67; 95% CI = -0.22, 0.34; ES difference = 0.36)
(Table 4). The change from baseline to post-study
was 1.6% (p > .05) and 7.3% (p > .05) for TOTAL and
SPLIT groups, respectively.
MT of the elbow extensors increased from
baseline to post-study by 8.6% (p < .001) and 15.7%
(p < .001) for TOTAL and SPLIT groups,
respectively, with no statistical differences noted
between groups (p = .62; 95% CI = -0.45, 0.27; ES
difference = 0.35) (Table 4).
Muscle strength
There was a significant main effect of time for
the 1RMBENCH (p = .033) and 1RMSQUAT (p = .0001).
1RMBENCH increased from baseline to post-study by
10.2% (p = .034) and 11.8% (p = .03) for TOTAL and
SPLIT groups, respectively, with no differences
noted between groups (p = .47; 95% CI = -13.75,
6.54; ES difference = 0.09) (Table 4). 1RMSQUAT
increased from baseline to post-study by 17.7% (p
= .011) and 18.9% (p =.006) for TOTAL and SPLIT
groups, respectively, with no differences noted
between groups (p = .60; 95% CI = -21.54, 12.61; ES
difference = 0.09) (Table 4).
Discussion
The present study is the first to investigate the
effects of training muscle groups two versus three
days per week in men with previous RT experience
while equating total training volume between
conditions using site-specific measures of muscle
growth. The primary and novel finding of our
study is that both RT frequencies elicited similar
increases in muscular strength and hypertrophy
over a 10-week program. The results are not in
agreement with our hypothesis that the TOTAL
group would experience greater increases in
muscle size and strength, and appear to refute the
hypothesis that increasing the frequency of MPS
stimulation with RT necessarily leads to enhanced
muscle protein accretion over time.
Both TOTAL and SPLIT produced significant
gains in maximal strength with marked increases
noted in the 1RMBENCH (10.2% and 11.8%,
respectively) and 1RMSQUAT (17.7% and 18.9%,
respectively). No statistical differences were found
between conditions and the ES differences were
minimal for both strength outcomes. These results
seem to be in line with several recent studies that
compared RT frequency prescription and were
done in resistance-trained individuals. For
example, Yue et al. (2018) compared training a
muscle group two versus four times per week with
volume equated between conditions and observed
no significant differences in strength gains
between the two groups. Brigatto et al. (2018)
compared strength gains over an 8-week period
between groups training a muscle group once
versus twice per week on a volume-equated basis.
Both groups increased their levels of strength in the
bench press and squat exercise post-intervention;
however, no significant differences between the
training groups were found. Furthermore, our
results corroborate meta-analytical data which
reported that when training volume was equated,
no significant effect of RT frequency on strength
gains was observed (Grgic et al., 2018).

140 Resistance training two vs. three days per week
Journal of Human Kinetics - volume 68/2019 http://www.johk.pl
Table 1
Training protocols
Protocol Monday Tuesday Wednesday Thursday Friday
TOTAL
(n=14)
Smith squat (4
sets)
Leg press (4 sets)
Leg extension (4
sets)
Bench press (4
sets)
Lat pulldown (4
sets)
Triceps pushdown
(4 sets)
Biceps curl (4 sets)
OFF
Smith squat (4
sets)
Leg press (4 sets)
Leg extension (4
sets)
Bench press (4
sets)
Lat pulldown (4
sets)
Triceps pushdown
(4 sets)
Biceps curl (4 sets)
OFF
Smith squat (4
sets)
Leg press (4 sets)
Leg extension (4
sets)
Bench press (4
sets)
Lat pulldown (4
sets)
Triceps pushdown
(4 sets)
Biceps curl (4 sets)
SPLIT
(n=14)
Smith squat (6
sets)
Leg press (6 sets)
Leg extension (6
sets)
Bench press (6
sets)
Lat pulldown (6
sets)
Triceps
pushdown (6 sets)
Biceps curl (6 sets)
OFF
Smith squat (6
sets)
Leg press (6
sets)
Leg extension
(6 sets)
Bench press (6
sets)
Lat pulldown (6
sets)
Triceps pushdown
(6 sets)
Biceps curl (6 sets)
Table 2
Dietary measures
TOTAL Initial TOTAL Final SPLIT Initial SPLIT Final
Calories
Carbohydrate (g)
Fat (g)
Protein (g)
2857.1 ± 811.9
372.9 ± 121.3
70.9 ± 37.5
192.0 ± 113.7
2804.9 ± 801.2
362.4 ± 107.6
69.1 ± 34.7
192.6 ± 96.5
2970.4 ± 530.1
393.4 ± 146.5
67.6 ± 32.2
197.1 ± 104.6
2987.1 ±
480.1
386.2 ± 131.7
70.1 ± 29.5
199.2 ± 89.0
Data are reported as mean ± SD
Table 3
Total volume load by exercise (kg)
Data are reported as mean ± SD.
Muscle Group TOTAL SPLIT
Bench press 62154.6 ± 27848.0 63428.9 ± 27848.0
Lat pulldown 63444.5 ± 21597.2 61491.4 ± 17635.5
Biceps curl 34527.7 ± 7749.4 31083.6 ± 7812.0
Triceps pushdown 59001.4 ± 25613.2 62426.8 ± 29094.2
Smith Squat 185532.7 ± 92670.7 158611.2 ± 33466.6
Leg Press 45º 244459.2 ± 61992.5 237917.1 ± 50199.9
Leg Extension 81486.4 ± 20664.1 79305.5 ± 16733.3

by Thiago Lasevicius et al. 141
© Editorial Committee of Journal of Human Kinetics
Table 4
Pre- to Post-study outcome measures
Data are reported as mean ± SD. Asterisk (*) indicates a significant effect from baseline
values. ES = effect size
These findings are somewhat
counterintuitive, as motor learning theory dictates
that practicing a given exercise more frequently
over time leads to better skill acquisition,
conceivably through neural enhancements (Shea et
al., 2000). Given our results, it may be speculated
that training twice a week is sufficient to optimize
neural proficiency in strength-related tasks, and
thereafter, training volume (and not frequency)
becomes the predominant factor for maximizing
results. Alternatively, it is possible that there is not
a sufficient difference between two versus three
weekly RT sessions from a frequency standpoint,
and perhaps higher frequencies are required to
promote additional neural improvements. That
said, this idea remains speculative given that
Colquhoun et al. (2018) and Saric et al. (2018)
recently compared volume-equated training three
versus six times per week and observed
comparable strength gains between the two
training frequencies. Further research is required
to develop a better understanding of these
complexities.
With respect to gains in muscle mass,
while both groups increased MT of the elbow
extensors and quadriceps following 10 weeks of
training, no significant between-group differences
were seen in the upper- or lower-body. No
previous studies have endeavored to evaluate site-
specific changes in muscle size when training
muscle groups two versus three days per week.
However, several volume-equated investigations
of training frequency have employed whole-body
measures of muscle mass including girth
measurements (Arazi and Asadi, 2011), air
displacement plethysmography (Benton et al.,
2011), and dual x-ray absorptiometry (Candow
and Burke, 2007), with no significant between-
group differences reported in all of these studies.
Schoenfeld et al. (2015) found greater increases in
elbow flexor MT and a trend for greater increases
in vastus lateralis MT when comparing volume-
equated groups training muscle groups three times
versus once per week. Brigatto et al. (2018)
compared training once versus twice per week
(over an 8-week training period) and reported no
significant differences in muscle hypertrophy
between the training groups. Based on the current
body of evidence, it is possible that variables such
as training volume may have a more profound
effect on muscular hypertrophy as compared to RT
frequency (Schoenfeld et al., 2017; Schoenfeld et al.,
2019). It should be noted that small, but potentially
meaningful ES differences (ranging from 0.31 to
0.39) were observed in favor of training muscles
two versus three days per week for every
hypertrophy outcome measure studied. These
findings suggest a potential hypertrophic benefit to
the lower training frequency. That said, additional
studies using direct measures of
Measure Total-Pre Total-Post ES Split-Pre Split-Post ES
Rectus Femoris (mm) 22.7 ± 2.5 24.5 ± 2.7* 0.71 22.7 ± 2.6 25.5 ± 2.2* 1.10
Vastus Lateralis (mm) 21.2 ± 3.4 23.8 ± 3.9* 0.83 21.3 ± 2.9 24.9 ± 3.1* 1.14
Elbow Flexors (mm) 35.9 ± 5.3 36.5 ± 6.0 0.11 34.3 ± 5.3 36.8 ± 4.7 0.47
Elbow Extensor (mm) 30.0 ± 5.6 32.6 ± 8.1* 0.43 29.9 ± 6.5 34.6 ± 5.8* 0.78
1RM Squat (kg) 156.5 ± 26.5 184.3 ± 31.2* 1.03 159.7 ± 27.7 190.0 ± 29.3* 1.12
1RM Bench Press (kg) 78.1 ± 19.8 86.1 ± 21.6* 0.45 80.9 ± 15.6 90.5 ± 17.3* 0.54

142 Resistance training two vs. three days per week
Journal of Human Kinetics - volume 68/2019 http://www.johk.pl
hypertrophy (i.e., ultrasound, magnetic resonance
imaging or computed tomography) are warranted
to explore this topic further. Also, studies with
longer duration time courses are needed given that
the majority of the current studies were six to 10
weeks in duration.
One possible limitation of the present
study is that it might have been slightly
underpowered from a statistical standpoint. We
initially recruited a sample of 36 participants;
however, eight participants did not complete the
whole training program, which subsequently
might have impacted the statistical power of the
study. Additionally, the sample was comprised of
young. trained men which therefore limits the
generalizability of the results to those who are
untrained, older, and women. Finally, the training
program lasted 10 weeks; it is possible that the
results would be different over longer time
courses.
Conclusions
Based on our findings, we conclude that
training muscle groups either twice or three times
per week results in similar increases in muscular
strength and hypertrophy in young adult trained
men when volume is equated between the training
conditions. The TOTAL protocol employed in this
study required fewer weekly sessions, but more
training time per session compared to SPLIT.
Alternatively, the SPLIT protocol required a higher
total number of weekly sessions, but each session
was of shorter duration compared to TOTAL.
Given the larger ESs favoring the SPLIT training
routine noted for hypertrophic outcomes, it
remains possible that small, but potentially
meaningful improvements may be elicited by
employing a training frequency of twice per week
as compared to training three times per week.
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Corresponding author:
Brad Jon Schoenfeld
Health Sciences Department, CUNY Lehman College,
Bronx, NY, 250 Bedford Park Blvd West, Bronx, NY 10468,
Phone: 718-960-1999;
E-mail: bradschoenfeldphd@gmail.com