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©Journal of Sports Science and Medicine (2016) 15, 715-722
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Received: 25 June 2016 / Accepted: 17 November 2016 / Published (online): 01 December 2016
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Differential Effects of Heavy versus Moderate Loads on Measures of Strength
and Hypertrophy in Resistance-Trained Men
Brad J. Schoenfeld 1, Bret Contreras 2, Andrew D. Vigotsky 3 and Mark Peterson 4
1 Department of Health Sciences, CUNY Lehman College, Bronx, NY, USA; 2 Sport Performance Research Institute,
AUT University, Auckland, New Zealand; 3 Kinesiology Program, Arizona State University, Phoenix, AZ, USA; 4 De-
partment of Physical Medicine and Rehabilitation, University of Michigan, Ann Arbor, MI
Abstract
The purpose of the present study was to evaluate muscular
adaptations between heavy- and moderate-load resistance train-
ing (RT) with all other variables controlled between conditions.
Nineteen resistance-trained men were randomly assigned to
either a strength-type RT routine (HEAVY) that trained in a
loading range of 2-4 repetitions per set (n = 10) or a hypertro-
phy-type RT routine (MODERATE) that trained in a loading
range of 8-12 repetitions per set (n = 9). Training was carried
out 3 days a week for 8 weeks. Both groups performed 3 sets of
7 exercises for the major muscle groups of the upper and lower
body. Subjects were tested pre- and post-study for: 1 repetition
maximum (RM) strength in the bench press and squat, upper
body muscle endurance, and muscle thickness of the elbow
flexors, elbow extensors, and lateral thigh. Results showed
statistically greater increases in 1RM squat strength favoring
HEAVY compared to MODERATE. Alternatively, statistically
greater increases in lateral thigh muscle thickness were noted for
MODERATE versus HEAVY. These findings indicate that
heavy load training is superior for maximal strength goals while
moderate load training is more suited to hypertrophy-related
goals when an equal number of sets are performed between
conditions.
Key words: Loading strategies, heavy loads, repetition range,
skeletal muscle hypertrophy, muscular adaptations.
Introduction
A generally accepted tenet in the field of exercise science
postulates that manipulation of resistance training (RT)
program variables is necessary to maximize muscular
adaptations (American College of Sports Medicine, 2009;
Baechle and Earle, 2008; Kraemer and Ratamess, 2004).
The intensity of load used, often delineated by repetition
ranges within various loading zones, is widely considered
amongst the most important of these variables. Training
with heavy loads at or near an individual’s 1 repetition
maximum (RM) necessarily results in fewer repetitions
completed when compared to training with lighter loads at
lower intensities. Consistent with the concept of a
strength-endurance continuum, the following loading
strategies have been proposed to maximize muscular
adaptations: a low-repetition loading zone (1-5RM) max-
imizes muscular strength; a moderate repetition loading
zone (8-12RM) maximizes muscular hypertrophy; and a
high-repetition loading zone (15+RM) maximizes muscu-
lar endurance (Baechle and Earle, 2008).
The volume of RT also has been shown to play a
role in muscular adaptations. There is evidence of a dose-
response relationship, whereby greater RT volumes are
associated with greater increases in strength (Krieger,
2009) and hypertrophy (Schoenfeld et al., 2016). Volume
load (VL), defined as the product of the total number of
repetitions performed for an exercise and the correspond-
ing amount of load, is affected by the loading zone em-
ployed; progressively higher VLs are seen as loading
proceeds to the right of the strength-endurance continuum
(Schoenfeld et al., 2014; 2015). Thus, a substantially
greater number of sets are required to equate volume load
between lower and higher loading zones. This can be
problematic when training at the far left of the strength-
endurance continuum, as high RT volumes combined with
heavy loads may chronically overstress the involved
joints and soft tissue structures as well as the central
nervous system (CNS), thereby increasing the potential
for overtraining and injury (Fry and Kraemer, 1997).
A number of studies have endeavored to investi-
gate the effects of low- versus moderate-loading zones on
muscular adaptations. The preponderance of research in
untrained individuals shows that strength gains are max-
imized with heavy load (1-5RM) training; these findings
are seen both when VL is equated (Campos et al., 2002),
as well as when an equal number of sets are performed
between conditions thus resulting in a lower VL for low
repetition training (Choi et al., 1998; Masuda et al., 1999).
Conversely, increases in hypertrophy have been shown to
be volume-dependent, with studies employing an equal
number of sets showing greater muscular growth for
moderate loading (Choi et al., 1998; Masuda et al., 1999)
and those equating VL showing no difference between
conditions (Campos et al., 2002).
To the authors’ knowledge, only 2 studies have in-
vestigated muscular adaptations to low- versus moderate-
loading schemes in resistance-trained subjects. This is
important, as adaptations during the initial stages of RT
are primarily related to improvements in the ability of the
CNS to efficiently coordinate muscles, whereas increases
in muscle mass are theorized to become increasingly more
relevant to strength-related improvements as one acquires
lifting experience (Sale, 1988; Schoenfeld, 2010). In
addition, emerging evidence shows that trained muscle
differs not only from a structural (Maughan at al., 1984;
Sale et al., 1987) and functional (Always et al., 1988;
Huczel and Clarke, 1992; Sale et al., 1983; Sale et al.,
1987) standpoint, but also displays altered RT responses
in intracellular anabolic signaling (Coffey et al., 2006),
Research article
Resistance training loading strategies
716
acute protein synthesis (Phillips et al., 1999; Tang et al.,
2008; Wilkinson et al., 2008), mitochondrial protein syn-
thesis (Wilkinson et al., 2008) and transcriptional upregu-
lation (Gordon et al., 2012).
Schoenfeld et al. (2014) carried out an 8-week
volume-equated study that randomized resistance-trained
men to train with either 7 sets at 3RM or 3 sets of 10RM.
Consistent with previous research in untrained subjects,
muscle hypertrophy was similar regardless of the load
lifted, but maximal strength was statistically greater when
training with heavier loads. Recently, Mangine et al.
(2015) randomized resistance-trained men to perform 4
sets with either 3-5RM or 10-12RM, so that VL was not
equated between conditions. As shown by others, strength
increases were greater with low- versus moderate-load
training. Interestingly and in opposition to the current
body of literature, however, some markers of muscle
growth also favored the low repetition condition. A poten-
tial confounding issue was that rest intervals were differ-
ent between conditions (3 min versus 1 min in heavy and
moderate loading, respectively), which may have unduly
influenced the generalizability of results to loading strate-
gies. The purpose of the present study was to evaluate
muscular adaptations between heavy- and moderate-load
training in resistance-trained men with all other RT varia-
bles controlled between conditions.
Methods
Subjects
Subjects were 26 male volunteers (age = 23.2 ± 4.2 years;
height = 1.75 ± 0.06 m; body mass = 84.3 ± 15.2 kg)
recruited from a university population. Subjects were
between the ages of 18-35, had no existing cardiorespira-
tory or musculoskeletal disorders, claimed to be free from
consumption of anabolic steroids or any other legal or
illegal agents known to increase muscle size currently and
for the previous year, and were considered experienced
lifters, defined as consistently lifting weights at least 3
times per week for at least 1 year. Seven subjects dropped
out of the study: 3 sustained minor training related inju-
ries; 1 sustained a non-training injury; and 3 withdrew for
personal reasons. Descriptive data for the 19 subjects who
completed the study are shown in Table 1.
Table 1. Baseline descriptive statistics. Data are expressed as
the mean (±SD).
VARIABLE
HEAVY
(n = 10)
MODERATE
(n = 9)
Age (yrs)
22.3 (3.9
24.1 (4.5)
Height (m)
1.74 (.08)
1.77 (.04)
Weight (kgs)
84.2 (16.6)
84.4 (14.5)
RT Experience (yrs)
4.3 (4.8)
5.2 (3.4)
Participants were pair-matched according to base-
line strength and then randomly assigned to 1 of 2 exper-
imental groups: a strength-type RT routine (HEAVY) that
trained in a loading range of 2-4 repetitions per set (n =
10) or a hypertrophy-type RT routine (MODERATE) that
trained in a loading range of 8-12 repetitions per set (n =
9). Approval for the study was obtained from the college
Institutional Review Board. Informed consent was ob-
tained from all participants prior to beginning the study. A
flow chart of the study design is presented in Figure 1.
Figure 1. Flow chart of study design.
Resistance training procedures
The RT protocol consisted of the following seven exercis-
es per session targeting major muscle groups of the body:
Flat barbell press, barbell military press, wide grip lat
pulldown, seated cable row, barbell back squat, machine
leg press, and machine leg extension. These exercises
were chosen based on their common inclusion in body-
building- and strength-type RT programs (Baechle and
Earle, 2008; Coburn and Malek, 2011). Subjects were
instructed to refrain from performing any additional re-
sistance-type or high-intensity anaerobic training for the
duration of the study.
Training for both routines consisted of 3 weekly
sessions performed on non-consecutive days for 8 weeks.
All sets were carried out to the point of momentary con-
centric muscular failure, operationally defined as the
inability to perform another concentric repetition while
maintaining proper form. Cadence of repetitions was
carried out in a controlled fashion, with a concentric ac-
tion of approximately one second and an eccentric action
of approximately two seconds. Subjects were afforded 2
minutes rest between sets. The load was adjusted for each
Schoenfeld et al.
exercise as needed on successive sets to ensure that sub-
jects achieved failure in the target repetition range. All
routines were directly supervised by the research team,
which included a National Strength and Conditioning
Association certified strength and conditioning specialist
and certified personal trainers, to ensure proper perfor-
mance of the respective routines. Attempts were made to
progressively increase the loads lifted each week within
the confines of maintaining the target repetition range.
Prior to beginning the training program, subjects in the
HEAVY group underwent 3-repetition maximum (RM)
testing and subjects in the MODERATE group underwent
10 RM testing to determine individual initial training
loads for each exercise. The RM testing was consistent
with recognized guidelines as established by the National
Strength and Conditioning Association (Baechle & Earle,
2008).
Dietary adherence
To avoid potential dietary confounding of results, subjects
were advised to maintain their customary nutritional reg-
imen and to avoid taking any supplements other than that
provided in the course of the study. Dietary adherence
was assessed by self-reported 5-day food records using
MyFitnessPal.com (http://www.myfitnesspal.com), which
were collected twice during the study: 1 week before the
first training session (i.e. baseline) and during the final
week of the training protocol. Subjects were instructed on
how to properly record all food items and their respective
portion sizes consumed for the designated period of inter-
est. Each item of food was individually entered into the
program, and the program provided relevant information
as to total energy consumption, as well as amount of en-
ergy derived from proteins, fats, and carbohydrates for
each time period analyzed. To maximize anabolism, sub-
jects were supplied with a supplement on training days
containing 25g protein and 1g carbohydrate (Iso100 Hy-
drolyzed Whey Protein Isolate, Dymatize Nutrition,
Farmers Branch, TX). The supplement was consumed
within 1 hour post-exercise, as this time frame has been
purported to help potentiate increases in muscle protein
synthesis following a bout of RT (Aragon & Schoenfeld,
2013).
Measurements
Muscle Thickness: Ultrasound imaging was used to ob-
tain measurements of muscle thickness (MT). The relia-
bility and validity of ultrasound in determining MT has
been reported to be very high when compared to the "gold
standard", magnetic resonance imaging (mean intraclass
correlation coefficients (ICC) of 0.998 and 0.999 for
reliability and validity, respectively) (Reeves et al., 2004).
A trained technician performed all testing using a B-mode
ultrasound imaging unit (ECO3, Chison Medical Imaging,
Ltd, Jiang Su Province, China). The technician applied a
water-soluble transmission gel (Aquasonic 100 Ultra-
sound Transmission gel, Parker Laboratories Inc., Fair-
field, NJ) to each measurement site, and a 5 MHz ultra-
sound probe was placed perpendicular to the tissue inter-
face without depressing the skin. When the quality of the
image was deemed to be satisfactory, the technician saved
the image to hard drive and obtained MT dimensions by
measuring the distance from the subcutaneous adipose
tissue-muscle interface to the muscle-bone interface, as
described previously (Abe et al., 2000). Measurements
were taken on the right side of the body at three sites: 1)
elbow flexors; 2) elbow extensors; and 3) lateral thigh.
For the anterior and posterior upper arm, measurements
were taken 60% distal between the lateral epicondyle of
the humerus and the acromion process of the scapula; for
the lateral thigh, measurements were taken 50% between
the lateral condyle of the femur and greater trochanter for
the quadriceps femoris. In an effort to ensure that swelling
in the muscles from training did not obscure results, im-
ages were obtained 48-72 hours before commencement of
the study, as well as after the final training session. This is
consistent with research showing that acute increases in
MT return to baseline within 48 hours following a RT
session (Ogasawara et al., 2012). To further ensure accu-
racy of measurements, 3 images were obtained for each
site and then averaged to obtain a final value. The test-
retest intraclass correlation coefficient (ICC) from our lab
for thickness measurement of the elbow flexors, elbow
extensors, and lateral thigh are 0.986, 0.981, and 0.997,
respectively. The standard errors of the measurement
(SEM) for these measures are 0.16, 0.50, and 0.25 mm,
respectively.
Muscle strength: Upper- and lower-body strength
was assessed by 1RM testing in the parallel back squat
(1RMSQUAT) and bench press (1RMBENCH) exercises.
These exercises were chosen because they are well-
established as measures of maximal strength. Subjects
reported to the laboratory having refrained from any exer-
cise other than activities of daily living for at least 48
hours prior to baseline testing and at least 48 hours prior
to testing at the conclusion of the study. Repetition max-
imum testing was consistent with recognized guidelines
established by the NSCA (Baechle and Earle, 2008). In
brief, subjects performed a general warm-up prior to test-
ing that consisted of light cardiovascular exercise lasting
approximately 5-10 minutes. A specific warm-up set of
the given exercise of 5 repetitions was performed at ~50%
of subjects’ perceived 1RM followed by one to two sets
of 2-3 repetitions at a load corresponding to ~60-80%
1RM. Subjects then performed sets of 1 repetition of
increasing load for 1RM determination. Three to 5
minutes rest was provided between each successive at-
tempt. All 1RM determinations were made within 5 trials.
In the 1RMSQUAT, subjects were required to squat down
so that the top of the thigh was parallel to the ground for
the attempt to be considered successful as determined by
a research assistant who was positioned laterally to the
subject. Successful 1RMBENCH was achieved if the
subject displayed a five-point body contact position (head,
upper back, and buttocks firmly on the bench with both
feet flat on the floor), lowered the bar to his chest, and
executed full elbow extension. 1RMSQUAT testing was
conducted prior to 1RMBENCH with at least a 5 minute
rest period separating tests. Strength testing took place
using barbell free weights. All testing sessions were su-
pervised by the research team to achieve a consensus for
success on each trial. The test-retest ICC for the
Resistance training loading strategies
718
1RMBENCH and 1RMSQUAT from our lab are 0.995
and 0.998, respectively. The SEM for these measures are
1.03 and 1.04 kgs, respectively.
Muscle endurance: Upper body muscular endur-
ance was assessed by performing bench press using 50%
of the subject’s initial 1RM in the bench press
(50%BENCH) for as many repetitions as possible to mus-
cular failure with proper form. Successful performance
was achieved if the subject displayed a five-point body
contact position (head, upper back, and buttocks firmly on
the bench with both feet flat on the floor), touched the bar
to his chest, and executed a full lock-out. Muscular en-
durance testing was carried out after assessment of mus-
cular strength to minimize the potential of metabolic
stress interfering with performance of the latter.
Statistical analyses
Descriptive statistics were used to explore the distribu-
tion, central tendency, and variation of each measurement.
An independent t-test was used to compare baseline val-
ues between groups. Descriptive statistics (means ± SE)
for each variable were reported at baseline, at 8 weeks,
and as percent change from baseline. In order to test dif-
ferences between groups, the proc reg procedure was used
to generate separate multiple linear regression models,
with post-intervention outcomes as the dependent variable
and baseline values as covariates. The model included a
group indicator with two levels and baseline values (cen-
tered at the mean values) as predictors. This modeling
approach is equivalent to an analysis of covariance, but
has the advantage of providing estimates associated with
each group, adjusted for baseline characteristics that are
potentially associated with the outcomes. This was also
important due to the fact that using change scores as the
dependent variable are subject to regression to the mean.
Each model included a group indicator with two levels
(0,1), as well as baseline values (centered at the mean
values) as predictors. Specifically, the coefficient for the
HEAVY group indicator was used to estimate the mean
difference in the outcome (e.g. MT change) associated
with HEAVY compared with MODERATE and the inter-
cept estimated the mean change in MODERATE. Regres-
sion assumptions were checked. Independent t-tests were
used to compare volume-load between groups. To quanti-
fy the magnitude of changes in outcome measures, effect
sizes were calculated using Hedges g (Cooper et al.,
2009). The following scale was used to categorize the
magnitude of effect: <0.2 = trivial; 0.2 - 0.5 = small; 0.5 -
0.8 = medium; 0.8 - 1.3 = large, and >1.3= very large.
Descriptive statistics and multiple regression was carried
out using SAS software version 9.3 (SAS Institute, Cary,
NC) with 2-sided 95% confidence intervals to determine
significance. Effect size calculations were computed us-
ing StataMP 13 (StataCorp LP, College Station, TX).
Results
No significant differences were noted between groups in
any baseline measure. Overall attendance for those who
completed the study was 89%, with no differences noted
between HEAVY and MODERATE conditions (91% vs
88%, respectively). Total aggregate weekly VL over the 8
weeks was significantly greater for MODERATE com-
pared to HEAVY (56049 ± 11101 vs 25867 ± 3731 kg,
respectively).
Muscle thickness
Significant increases in MT of the elbow flexors were
noted for both HEAVY (p = 0.02) and MODERATE (p <
0.001) groups from baseline to post-study. No significant
between-group differences were noted between conditions
(p = 0.19). Effect sizes favored MODERATE compared
to HEAVY (0.42 versus 0.28, respectfully), with both
conditions showing small effects (see Table 2).
A significant increase in MT of the elbow exten-
sors was noted for the MODERATE (p = 0.02) but not the
HEAVY (p = 0.25) group from baseline to post-study. No
significant between-group differences were noted be-
tween conditions (p = 0.74). Effect sizes were similar
between MODERATE and HEAVY (0.21 versus 0.17,
respectfully), with both conditions showing trivial to
small effects (see Table 2).
Significant increases in MT of the lateral thigh
were noted for both HEAVY (p = 0.02) and MODERATE
(p < 0.001) groups from baseline to post-study. A signifi-
cant between-group difference was noted such that
MODERATE produced superior results compared to
HEAVY (p = 0.007). Effect sizes markedly favored
MODERATE compared to HEAVY (1.17 versus 0.33,
respectfully), with MODERATE showing a large effect
and HEAVY showing a small effect (see Table 2).
Maximal strength
Both HEAVY and MODERATE groups showed a signif-
icant increase in 1RMBENCH from baseline to post-study
(all p < 0.01). No significant between-group differences
were noted between conditions (p = 0.07). Effect sizes
favored HEAVY compared to MODERATE (0.67 versus
0.38, respectfully), with HEAVY showing a medium
effect and MODERATE showing a small effect (see Ta-
ble 3). Both HEAVY and MODERATE groups showed a
significant increase in 1RMSQUAT from baseline to
post-study (all p = 0.001). A significant between-group
difference was noted such that HEAVY produced superi-
or results compared to MODERATE (p = 0.03). Effect
sizes markedly favored HEAVY compared to
MODERATE (1.12 versus 0.71, respectfully), with
HEAVY showing a large effect and MODERATE
Table 2. Pre- vs. Post-Study muscle thickness. Data are expressed as the mean (±SD) in mm.
OUTCOME
MEASURE
HEAVY
MODERATE
PRE-STUDY
POST-STUDY
HEDGE’S G
PRE-STUDY
POST-STUDY
HEDGE’S G
Elbow Flexors
46.7 (4.4)
48.1 (4.8) *
.28
46.9 (5.3)
49.2 (5.3) *
.42
Elbow Extensors
47.3 (8.0)
48.6 (7.2)
.17
48.4 (7.2)
49.9 (6.6) *
.21
Lateral Thigh
56.5 (5.8)
58.8 (7.1) *
.33
56.0 (4.7)
61.8 (4.7) *#
1.17
An asterisk (*) indicates a significant effect from baseline values. A number sign (#) indicates a significant difference between groups.
Schoenfeld et al.
Table 3. Pre- vs. Post-Study Muscle Strength. Data are expressed as the mean (±SD) in kgs.
OUTCOME
MEASURE
HEAVY
MODERATE
PRE-STUDY
POST-STUDY
HEDGE’S G
PRE-STUDY
POST-STUDY
HEDGE’S G
1RMBENCH
92.7 (19.3
106.1 (18.9) *
.67
95.5 (23.8)
105.5 (26.3) *
.38
1RMSQUAT
114.5 (30.8)
148.9 (27.7) *#
1.12
119.5 (26.0)
139.4 (27.2) *
.71
An asterisk (*) indicates a significant effect from baseline values. A number sign (#) indicates a significant difference between groups.
Table 4. Pre- vs. Post-Study Muscle Endurance. Data are expressed as the mean (±SD) in repetitions.
OUTCOME
MEASURE
HEAVY
MODERATE
PRE-STUDY
POST-STUDY
HEDGE’S G
PRE-STUDY
POST-STUDY
HEDGE’S G
50%BENCH
25.2 (3.4)
31.9 (5.9) *
1.32
28.8 (3.5)
34.7 (5.5) *
1.21
An asterisk (*) indicates a significant effect from baseline values. A number sign (#) indicates a significant difference between groups.
showing a medium effect. (see Table 3).
Muscular endurance
Both HEAVY and MODERATE groups showed a signif-
icant increase in 50%BENCH from baseline to post-study
(all p < 0.01). No significant between-group differences
were noted between conditions (p = 0.07). Effect sizes
were similar between HEAVY and MODERATE (1.32
versus 1.21, respectfully), with both conditions showing
large to very large effects (see Table 4).
Nutrition
Analysis of self-reported dietary records revealed that
total protein intake was statistically greater for
MODERATE versus HEAVY at baseline (1.4 g/kg versus
1.9 g/kg, respectively; p = 0.005), but these differences
abated by study's end (1.7 g/kg versus 1.8 g/kg, respec-
tively; p = 0.63). Subjects in HEAVY statistically in-
creased the amount of calories (p = 0.02) consumed from
pre- to post-study, but total intake was not statistically
different between groups at either time point. No other
statistical differences in nutrition were noted either be-
tween or within groups. Results of nutritional data are
illustrated in Figure 2.
Discussion
The present study showed that training with heavy versus
moderate loads elicits differential effects on muscular
strength and hypertrophy. Increases in 1RMSQUAT were
significantly greater in HEAVY compared to
MODERATE (30.0% versus 16.8%, respectively) with
HEAVY showing a large magnitude of effect compared to
a medium effect in MODERATE (1.12 versus 0.71, re-
spectively). Increases in 1RMBENCH also favored
HEAVY versus MODERATE (14.4% versus 10.5%,
respectively), and given the low p-value (p = 0.07) and
relatively small sample size, non-significant results may
be attributed to a type II error. Indeed, effects sizes sug-
gested a meaningful difference in 1RMBENCH, with
HEAVY showing a medium effect compared to a small
effect for MODERATE (0.62 versus 0.46, respectfully).
Our findings are in line with those of Mangine et al.
(2015), who also found greater strength improvements
when resistance-trained men trained at 3-5RM versus 10-
12RM. Similar results have been reported in untrained
individuals as well (Choi et al., 1998; Masuda et al.,
1999). The totality of these findings provide compelling
evidence that specificity of training at the far left of the
Figure 2. Graphical representation of nutritional intake pre- and post-intervention for HEAVY and
MODERATE, mean (±SD).
Resistance training loading strategies
720
strength-endurance continuum is preserved even when
weekly RT volume is markedly lower; while RT volume
has been shown to play a role in strength-related out-
comes (Krieger, 2009), higher intensities of load appear to
be of paramount importance.
Although the underlying mechanisms remain to be
determined, it can be speculated that neural adaptations
associated with training close to one’s 1RM were respon-
sible for the superior strength increases when using heavy
loads. There is evidence that the biomechanics of multi-
joint exercise performance change with alterations in
intensity of load. For example, the ratio of hip-to-knee
extensor moments has been found to increase with heavier
loads during squats, lunges, deadlifts, and hex-bar dead-
lifts (Beardsley and Contreras, 2014). Therefore, motor
pattern coordination conceivably is optimized by practic-
ing an exercise with the form most specific to that which
will be used in the maximal lift.
It is unclear as to whether in vivo normalized force
production, or its homologous counterpart, specific ten-
sion, increases, decreases, or remains the same following
training, as research is equivocal on the topic (Erskine et
al., 2010; Kawakami et al., 1995; Narici and Kayser,
1995). While no training studies have endeavored to elu-
cidate the role of loading zones in such phenomena, cross-
sectional data suggests that bodybuilders, who normally
train closer to the hypertrophy loading zone, have larger
muscles with lower normalized force and specific tension
than power athletes (Ikegawa et al., 2008; Meijer et al.,
2015). Therefore, it is conceivable that specific tension
changes may have occurred in one or both groups, and
that such a response is at least partially responsible for
greater strength outcomes in the HEAVY group with
greater hypertrophic responses in the MODERATE
group. Additional research is needed to delineate such
mechanisms.
In contrast to strength-related adaptations, training
with moderate loads tended to produce superior increases
in MT compared to heavy-load training. This finding was
particularly evident in the lateral quadriceps femoris,
where statistically greater increases in muscle thickness
were observed in MODERATE compared to HEAVY
(10.4% versus 4.1%, respectively). Moreover,
MODERATE showed a large magnitude of effect while
HEAVY showed a small effect (1.17 versus 0.33, respec-
tively), indicating that differences were indeed meaning-
ful. Although no statistical differences were found in MT
of the upper arms, ES differences in the elbow flexors
showed a modest superiority for the MODERATE condi-
tion as well. These results run contrary to those of Man-
gine et al. (2015), who found similar improvements in
MT between moderate versus heavy load training, and in
fact noted greater increases in lean arm mass as deter-
mined by dual-energy X-ray absorptiometry. The discrep-
ant findings between studies are not clear, but may at least
in part be due to differences in the length of rest intervals.
While our study equated rest intervals between conditions
(2 minutes rest between sets), Mangine et al. (2015) em-
ployed a 3-minute rest interval for the heavy load condi-
tion and a 1-minute rest interval for the light-load condi-
tion. Recent work from our lab found that taking short
rest periods (1 minute) attenuated the hypertrophic re-
sponse to RT (Schoenfeld et al., 2016), and it is possible
that the reduced rest periods used by Mangine et al.
(2015) compromised muscular gains. This hypothesis
warrants further investigation.
There is evidence of a dose-response relationship
between RT volume and muscle hypertrophy, with greater
volumes resulting in greater gains in muscle mass
(Schoenfeld et al., 2016). Given that weekly VL for
MODERATE was more than double that for HEAVY,
this could seemingly explain the superior gains in muscle
growth seen with moderate load training in the present
study. Previous work from our lab showed similar in-
creases in growth of the elbow flexors in resistance-
trained men when volume was equated between moderate
and heavy load conditions (Schoenfeld et al., 2014), lend-
ing support to the hypothesis that RT volume is a primary
driver of muscle hypertrophy.
Improvements in upper body muscle endurance
were found to be similar between conditions, with large to
very large ESs noted for both HEAVY and MODERATE
(1.32 versus 1.21, respectively). On the surface, these
findings run contrary to the principle of specificity, which
dictates that greater increases in muscle endurance are
seen when training in higher repetition ranges. However,
testing for 50%BENCH was based on the subjects’ base-
line 1RM bench press. The larger increases in maximal
strength for HEAVY compared to MODERATE across
the study period therefore resulted in HEAVY performing
post-testing at a lower percentage of 1RM. Previous re-
search from our lab found that training in a higher repeti-
tion range (25-35 RM) elicited greater increases in upper
body muscle endurance compared to training in a moder-
ate repetition range when loads were readjusted based on
post-study increases in 1RM (Schoenfeld et al., 2015).
Whether very high repetition ranges (> 20 RM) confer
greater effects on muscle endurance when loads are not
readjusted remains undetermined.
The present study had several limitations that
should be taken into account when attempting to draw
evidence-based conclusions from results. First, measure-
ments of MT were obtained only at the mid-portion of
each muscle. Although this assessment can be considered
a proxy of overall growth of a given muscle, there is evi-
dence that hypertrophy often manifests in a non-uniform
manner, with greater muscle protein accretion seen in the
proximal or distal aspects (Wakahara et al., 2012; 2013).
We therefore cannot rule out the possibility that discrep-
ant hypertrophic changes may have taken place to a great-
er extent proximally or distally in one condition versus
the other, which would not have been observed in our
protocol. Moreover, it remains possible that changes in
MT as assessed by ultrasound may be confounded by
edema associated with muscle damage, although this
event seems unlikely given that subjects were experienced
in resistance training and thus the repeated bout effect
would have diminished the potential for damage, particu-
larly over the course of an 8-week training period.
Second, results may have been influenced by the
novelty factor of changing programs. Pre-study interviews
revealed that 16 of the 19 subjects regularly trained with
Schoenfeld et al.
loads ≥8RM, and only one subject reported regularly
using loads <5RM. Given evidence that the muscular
response is heightened when RT program variables are
altered outside of traditional norms (Kraemer et al.,
2003), it is feasible that subjects in HEAVY unduly bene-
fited from the unfamiliar stimulus of training in a low
repetition range. This hypothesis merits further study.
Finally, our findings are specific to young re-
sistance-trained men and cannot necessarily be general-
ized to other populations. It is well-documented that ado-
lescents, women, and the elderly respond differently to
RT compared to young adult men. Future research should
endeavor to investigate muscular adaptations in low-
versus moderate-load RT across populations.
Conclusion
Our findings provide evidence that training in different
loading zones elicit differential muscular adaptations in
resistance-trained men when an equal number of sets are
performed. Although the mechanisms remain undeter-
mined, we can infer that strength related adaptations are
maximized by training closer to one’s 1RM. Alternative-
ly, increases in muscle size seem to be driven more by
higher training volumes, at least up to a certain threshold.
It is conceivable that combining loading strategies may
have a synergistic effect on strength and hypertrophic
improvements. This hypothesis warrants further investiga-
tion.
Acknowledgments
This study was supported by a grant from PSC-CUNY. The authors
gratefully acknowledge the contributions of Robert Harris, Geronimo
Branagan, Miguel Alemar, Fanny Chen, Brandon Kwong, Gabriel
Sanchez, Cameron Yuen, Steve Hamilton, Osvaldo Gonzalez, and Diego
Martinez in their indispensable role as research assistants in this study.
We also would like to express our gratitude to Dymatize Nutrition for
providing the protein supplements used in this study. The authors report
no conflicts of interest with this manuscript.
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Key points
Heavy loads maximize muscular strength when the
numbers of sets are equated.
Moderate loads maximize muscle hypertrophy
when the number of sets are equated
Volume load appears to be more important to in-
creases in muscle hypertrophy compared to abso-
lute strength
AUTHOR BIOGRAPHY
Brad J. SCHOENFELD
Employment
Assistant Professor, Lehman College,
Health Sciences Department, Bronx, NY
Degree
PhD
Research interests
Optimizing body composition through
exercise and nutritional interventions
E-mail: brad@workout911.com
Bret CONTRERAS
Employment
Owner of BC Athletics
Degree
PhD
Research interests
The effects of gluteus maximus strength-
ening on performance
Andrew VIGOTSKY
Employment
Student
Degree
BSc
Research interests
Elucidating the mechanisms of human
movement
Mark PETERSON
Employment
Department of Physical Medicine and
Rehabilitation, University of Michigan
Health System
Degree
PhD
Research interests
Mechanisms of secondary muscle pathol-
ogy and metabolic dysregulation in adults
with cerebral palsy; Predictors of muscle
aging; Resistance exercise for metabolic
health
Brad J. Schoenfeld
Department of Health Sciences, CUNY Lehman College, Bronx,
NY, USA
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