The effects of squat variations on strength and quadriceps hypertrophy adaptations in recreationally trained females

Abstract

The barbell squat is a multijoint exercise often employed by athletes and fitness enthusiasts due to its beneficial effects on functional and morphological neuromuscular adaptations. This study compared the effects of squat variations on lower limb muscle strength and hypertrophy adaptations. Twenty‐four recreationally trained females were assigned to a 12‐week front squat (FS; n = 12) or back squat (BS; n = 12) resistance training protocol (twice per week). Maximum dynamic strength (1‐RM) on the 45° leg press, a nonspecific strength test, and muscle thickness of the proximal, middle, and distal portions of the lateral thigh were assessed at baseline and post‐training. A significant time versus group interaction was observed for 1‐RM values (F(1,22) = 10.53; p = 0.0004), indicating that BS training elicits greater improvements in muscle strength compared with FS training (p = 0.048). No time versus group interactions were found for muscle thickness (F(1,22) = 0.103; p = 0.752); however, there was a significant main effect of time for the proximal (F(1,22) = 7.794; p = 0.011), middle (F(1,22) = 7.091; p = 0.014), and distal portions (F(1,22) = 7.220; p = 0.013) of the lateral thigh. There were no between‐group differences for any muscle thickness portion (proximal: p = 0.971; middle: p = 0.844; and distal: p = 0.510). Our findings suggest that BS elicits greater improvements in lower limb muscle strength on the 45° leg press than FS, but hypertrophic adaptations are similar regardless of variations during the squat exercise.

Full text

Received: 15 December 2022
-
Revised: 22 August 2023
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Accepted: 4 September 2023
DOI: 10.1002/ejsc.12042
ORIGINAL PAPER
The effects of squat variations on strength and quadriceps
hypertrophy adaptations in recreationally trained females
Alysson Enes
1
|Gustavo Oneda
2
|Danilo Fonseca Leonel
3
|Lucas Lemos
1
|
Felipe Alves
1
|Luis H. B. Ferreira
1
|Guillermo Escalante
4
|
Brad J. Schoenfeld
5
|Tácito P. Souza‐Junior
1
1
Metabolism, Nutrition and Strength Training
Research Group, Federal University of Paraná
(UFPR), Curitiba, Brazil
2
Department of Physical Education, Sports
Center, Federal University of Santa Catarina
(UFSC), Florianópolis, Brazil
3
Department of Physical Education, Federal
University of Jequitinhonha and Mucuri
Valleys, Diamantina, Brazil
4
Department of Kinesiology, California State
University (CSU), San Bernardino, California,
USA
5
Department of Exercise Science and
Recreation, CUNY Lehman College, Bronx,
New York, USA
Correspondence
Alysson Enes, Department of Physical
Education, Metabolism, Nutrition and
Strength Training Research Group, Federal
University of Paraná, Rua Coronel Francisco
Heráclito dos Santos, 210, Curitiba, PR
81531‐980, Brazil. Email: alysson.
enes@hotmail.com
Funding information
Coordination for the Improvement of Higher
Education Personnel
Abstract
The barbell squat is a multijoint exercise often employed by athletes and fitness
enthusiasts due to its beneficial effects on functional and morphological neuro-
muscular adaptations. This study compared the effects of squat variations on lower
limb muscle strength and hypertrophy adaptations. Twenty‐four recreationally
trained females were assigned to a 12‐week front squat (FS; n=12) or back squat
(BS; n=12) resistance training protocol (twice per week). Maximum dynamic
strength (1‐RM) on the 45° leg press, a nonspecific strength test, and muscle
thickness of the proximal, middle, and distal portions of the lateral thigh were
assessed at baseline and post‐training. A significant time versus group interaction
was observed for 1‐RM values (F
(1,22)
=10.53; p=0.0004), indicating that BS
training elicits greater improvements in muscle strength compared with FS training
(p=0.048). No time versus group interactions were found for muscle thickness
(F
(1,22)
=0.103; p=0.752); however, there was a significant main effect of time for
the proximal (F
(1,22)
=7.794; p=0.011), middle (F
(1,22)
=7.091; p=0.014), and
distal portions (F
(1,22)
=7.220; p=0.013) of the lateral thigh. There were no
between‐group differences for any muscle thickness portion (proximal: p=0.971;
middle: p=0.844; and distal: p=0.510). Our findings suggest that BS elicits greater
improvements in lower limb muscle strength on the 45° leg press than FS, but
hypertrophic adaptations are similar regardless of variations during the squat
exercise.
KEYWORDS
back squat, front squat, muscle thickness, muscular strength, quadriceps femoris
Highlights
�Back squat training elicited greater strength‐related improvements in a nonspecific strength
test than front squat training.
�Hypertrophic adaptations of the lateral thigh are similar between both squat variations.
This is an open access article under the terms of the Creative Commons Attribution‐NonCommercial‐NoDerivs License, which permits use and distribution in any
medium, provided the original work is properly cited, the use is non‐commercial and no modifications or adaptations are made.
© 2024 The Authors. European Journal of Sport Science published by Wiley‐VCH GmbH on behalf of European College of Sport Science.
6
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Eur J Sport Sci. 2024;24:6–15. wileyonlinelibrary.com/journal/ejsc

�Both squat variations elicited similar growth at proximal, middle, and distal regions of the
lateral thigh.
1
|
INTRODUCTION
The squat is a frequently used lower limb exercise in resistance
training (RT) programs where the goal is to increase strength,
power, conditioning, and/or rehabilitation. The barbell squat is a
multijoint exercise often employed by athletes and fitness enthusi-
asts due to its beneficial effects on functional and morphological
neuromuscular adaptations (Ribeiro et al., 2022; B. J. Schoen-
feld, 2010). This exercise has variations that allowed previous
studies to investigate squat depth (Bloomquist et al., 2013; Kubo
et al., 2019; Pallarés et al., 2020), stance width (Sinclair et al., 2022),
foot placement (Lorenzetti et al., 2018), movement tempo (Morris-
sey et al., 1998; Usui et al., 2016), and barbell position (Contreras
et al., 2016; Korak et al., 2018). Among these variations, the front
squat (FS) and back squat (BS) are common squat variations that
alter the placement of the barbell by bracing the barbell either along
the clavicle or posteriorly near the level of the acromion, respec-
tively. This difference in barbell position creates biomechanical dif-
ferences between both squat forms, such as an upright torso and
less hip flexion with the FS and a prominent forward torso and more
hip flexion during BS (B. J. Schoenfeld, 2010). Due to these kine-
matic differences, previous studies that compared the FS and BS
have observed differences in joint kinetics between the two varia-
tions (Contreras et al., 2016; Gullett et al., 2009; Korak et al., 2018;
Krzyszkowski & Kipp, 2020; Yavuz & Erdag, 2017). For example,
evidence shows that surface electromyographic activity of thigh
muscles is generally similar between FS and BS in healthy women
(Contreras et al., 2016; Korak et al., 2018) and competitive body-
builders (Coratella et al., 2021).
The BS and FS are common exercises prescribed in RT programs
that aim to develop muscle strength, since the lower limb muscula-
ture is used in common sport‐related tasks (i.e., sprinting, jumping,
and squatting) (B. J. Schoenfeld, 2010; Stone et al., 2022). Previous
studies have investigated the effect of exercise selection, variation,
and mode on muscle strength and found that strength‐related im-
provements were primarily driven by specificity, that is, if the goal is
to increase strength in an exercise or task, the specific exercise or
task must be preferentially practiced, even though adding accessory
exercises may provide advantages or reduce strength adaptations in
a specific task (Chaves et al., 2020; Costa et al., 2022; Lee et al., 2018;
Remaud et al., 2010; Rossi et al., 2018). There are biomechanical
differences between FS and BS that conceivably could influence
neural adaptations. Hence, employing the FS or BS for dynamic
strength testing could bias results since the strength gains might be
specific to “practicing” the test during weekly training sessions
(Mattocks et al., 2017). Thus, selecting a neutral testing modality,
such as a different multijoint lower limb exercise, could help to
ensure that results are related to the effect of the exercise and not a
possible effect of specificity.
Despite evidence of similar kinematics and electromyographic
activity between the FS and BS in healthy females, these variations
appear to produce differences in kinetics. Gullet et al. (2009) found
that FS elicits significantly lower compressive forces at the knee joint
and reduced lumbar stress compared to the BS; however, there were
no statistical differences in electromyographic activity in thigh mus-
cles. Indeed, previous studies showed that varying the barbell posi-
tion could shift the center of mass forward and alter peak hip
extensor net internal joint moment between the FS and BS (Braidot
et al., 2007; Korak et al., 2018; Krzyszkowski & Kipp, 2020). These
shifts in the center of mass and net internal joint moments might
alter torque relationships between the hip/knee joints and muscles,
which in turn could increase mechanical tension at different muscle
lengths during these squat executions and potentially elicit inhomo-
geneous hypertrophy along the quadriceps femoris (Earp et al., 2015;
Ema et al., 2013; Mangine et al., 2018). Furthermore, training volume
could be a confounding variable regarding muscular adaptations
(Baz‐Valle et al., 2022; Ralston et al., 2017). Emerging evidence
suggests that participants' previous RT volume, quantified by the
number of sets performed per week per muscle group, could have an
influence on muscular adaptations (Aube et al., 2022; Scarpelli
et al., 2020). Thus, employing an individualized approach to training
volume based on participants' previous quadriceps sets volume may
help to reduce this confounding effect.
Previous research comparing the BS and FS has focused on acute
data relating to biomechanical aspects, thereby limiting the ability to
draw inferences regarding longitudinal muscular adaptations (Vig-
otsky et al., 2022). To date, evidence is lacking as to the chronic ef-
fects of BS versus FS training on strength and hypertrophy
adaptations using an individualized training approach based on
the previous volume in healthy females. Considering the gaps in the
current literature, the purpose of this study was to investigate the
effects of the FS and BS on dynamic strength and regional hyper-
trophy adaptations of the quadriceps femoris in healthy, recrea-
tionally trained females. We hypothesized that varying the barbell
position would elicit distinct strength and inhomogeneous hyper-
trophy responses in healthy females.
2
|
METHODS
2.1
|
Study design
We employed a randomized, repeated‐measures parallel‐group
design, balanced according to dynamic strength, to investigate
the effects of squat variations on strength and hypertrophy adap-
tations in healthy, recreationally‐trained females. The study began
with anthropometric assessments, quadriceps muscle thickness im-
aging, and familiarization sessions. The anthropometric assessment
EUROPEAN JOURNAL OF SPORT SCIENCE
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7

was performed using a multifrequency bioelectrical impedance
(InBody 120) to assess body mass and body fat percentage, and
height was assessed with a stadiometer (W200/5). As per the
guidelines provided by the manufacturer, participants were
instructed to (i) refrain from consuming any food or water for a
minimum of 2 h prior to the evaluation; (ii) abstain from consuming
beverages containing alcohol or caffeine within a 24‐h period
leading up to the evaluation; (iii) avoid engaging in moderate to
vigorous physical activity within 12 h before the evaluation; (iv)
consume water of at least 2 L on the day preceding the evaluation;
and (v) if possible, urinate 30 min before the evaluation. After
familiarization sessions, participants underwent 1‐RM tests on the
45° leg press. Afterward, participants undertook a progressive RT
program that aimed to compare the effects of the barbell FS versus
BS on strength and hypertrophy adaptations.
After baseline assessments, participants were allocated to either
the FS or the BS group. Initially, participants began the training
program with a weekly set volume of 20% more than their previous
quadriceps training volume. The weekly quadriceps training volume
was increased by 20% every 4 weeks (B. Schoenfeld et al., 2021).
Total training volume (TTV) was monitored but not equated to
maintain ecological validity as BS training allows the use of greater
absolute loads than FS (Yavuz & Erdag, 2017). Seventy‐two hours
after the last training session, lateral thigh muscle thickness and 1‐
RM tests were conducted in the same manner as baseline.
2.2
|
Subjects
The sample power was calculated using the software G*Power 3.1 for
F family analysis of variance (ANOVA) repeated measures, within‐
factors, to determine a sufficient number of participants to meet
the study purpose with the following conditions: Power =0.80,
α=0.05, a moderate effect size of 0.25, and correlation among
repeated measures of 0.7. The analysis indicated that 22 participants
were required to achieve adequate statistical power. To account for
potential dropouts, we recruited 29 healthy females and allocated
them to either the FS group (n=15) or the BS group (n=14).
Randomization was pair‐matched based on the initial maximum dy-
namic strength (1‐RM) in the 45° leg press.
We employed the following inclusion criteria for the study: (a)
age 18–30 years; (b) at least 6 months of RT practice at 4 days per
week of RT frequency; (c) negative answers to all items of the
Physical Activity Readiness Questionnaire; (d) free from creatine
supplementation; and (e) self‐report of the use of at least 3 months of
combined oral contraceptive pills with consumption and withdrawal
phases according to individual menstrual cycle length. The exclusion
criteria were as follows: (a) self‐report of any musculoskeletal injury;
(b) self‐report of alcohol abuse; (c) self‐report of anti‐inflammatory
or anabolic androgenic steroids use; and (d) self‐report of any men-
strual irregularities. Participants were informed of the procedures
and details related to training intervention and signed a written
informed consent form prior to their participation. All procedures
were submitted and approved by the local ethics committee and
were in accordance with the Declaration of Helsinki.
2.3
|
Maximum dynamic strength (1‐RM)
Participants completed two familiarization sessions before the 1‐RM
45° leg press tests at baseline. These familiarization sessions con-
sisted of instructions for technical standards for each exercise that
would be used during the training program. Both familiarization
sessions were conducted with the same procedures as used during 1‐
RM testing (i.e., warm‐up and rest between sets); however, partici-
pants used close to but not maximum loads. Each familiarization
session was conducted 48h apart. Seventy‐two hours after the final
familiarization session, participants performed the first 1‐RM testing
session, and the second 1‐RM session was conducted 72 h later. The
highest 1RM value between the two testing sessions was considered
for the analysis.
Both familiarization sessions and 1‐RM tests were carried out
as follows: participants performed a general warm‐up (5 min at
6 km.h
−1
at a treadmill and a light full‐body stretching routine)
followed by a specific warm‐up of 2 sets of 5 repetitions at an
estimated load for 12 and 8 repetitions, respectively, with 2‐min
rest interval between sets. Participants received specific in-
structions regarding the 45° leg press technique (e.g., full range of
motion with the knees brought as close as possible to the chest).
Three min after the specific warm‐up, 1‐RM attempts began. The
load was progressively increased until participants were unable to
perform the correct 45° leg press with proper form (e.g., knee
flexion less than ~100°), which was monitored by the research
team. The 1‐RM load was determined within 5 attempts, with 3–
5 min passive recovery provided between attempts (Brown &
Weir, 2001). The postintervention 1‐RM testing was conducted
after ultrasound imaging. The coefficient of variation (CV), standard
error of measurement (SEM), and intraclass correlation coefficient
with 95% confidence interval (ICC) between two 1‐RM tests per-
formed 72 h apart were 3.85%, 5 kg, and 0.95 (0.90–0.98),
respectively.
2.4
|
Muscle thickness
A B‐mode ultrasound (ECO3, Chison Medical Imaging Ltd.) with a 5‐
MHz linear transducer was used to obtain muscle thickness mea-
surements of the lateral quadriceps as assessed along the proximal
(30%), middle (50%), and distal (70%) aspects, considered as the
distance from the greater trochanter to the lateral condyle of the
femur (Abe et al., 2000). These anatomical points were detected by
palpation. We then measured femur length with an anatomical
pachymeter, registering the femur length of each participant as well
as the respective proximal, middle, and distal aspects of lateral thigh
muscles, which were transversally marked to guide imaging
(Figure 2). Participants were instructed to refrain from any strenuous
8
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ENES
ET AL.

exercise or other moderate‐to‐vigorous physical activity 72 h prior to
ultrasound imaging to avoid the potential influence of muscle
swelling on the primary outcome. Upon arriving at the lab, partici-
pants assumed the supine position with all joints relaxed and the
knees slightly flexed during image acquisition. Participants were
asked which lower limb they would use to kick a ball to determine the
dominant lower limb for image acquisition.
A trained ultrasound technician, blinded to group allocation,
applied a generous amount of water‐soluble transmission gel to each
portion of the lateral thigh. Transverse images were obtained by
placing the linear transducer on the skin with caution taken not to
depress the skin. When an appropriate image was obtained, it was
saved to the hard drive. Muscle thickness was measured as the dis-
tance between the internal border of the superficial aponeurosis of
the vastus lateralis and external border of the femur, providing a
combined measure of muscle thickness of the vastus lateralis and
vastus intermedius (Figure 2). Each portion of the lateral thigh had
three images captured, and measurements were averaged to obtain a
final value. If one of the three images showed a difference greater
than 10%, a fourth image was taken and replaced with the closest
value. We did not consider the menstrual cycle phase to evaluate the
muscle thickness at baseline and post‐training, since neither the
FIGURE 2 Thigh regions and an ultrasound image. Estimation plot of the paired mean difference for hypertrophic responses for proximal
(30%; A), middle (50%; B), and distal (70%; C) regions of lateral thigh for within‐subjects (top) and between‐groups (bottom) conditions. The
raw data are plotted on the upper axes; each paired set of observations is connected by a line. On the lower axes, each paired mean difference
is plotted as a bootstrap sampling distribution. Mean differences are depicted as dots; 95% confidence intervals are indicated by the ends of
the vertical error bars. BS, back squat; F, femur; FS, front squat; mm, millimeters; VI, vastus intermedius; VL, vastus lateralis.
FIGURE 1 Estimation plot of the paired mean difference 1‐RM
changes in the 45° leg press for within‐subjects and between‐
groups conditions. The raw data are plotted on the upper axes; each
paired set of observations is connected by a line. On the lower axes,
each paired mean difference is plotted as a bootstrap sampling
distribution. Mean differences are depicted as dots; 95% confidence
intervals are indicated by the ends of the vertical error bars.
*=significantly differences between groups (p<0.05); BS, back
squat; FS, front squat; kg, kilograms.
EUROPEAN JOURNAL OF SPORT SCIENCE
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menstrual cycle phase nor the use of contraceptive oral pills seems to
influence muscle thickness measurement (Kuehne et al., 2021; Sung
et al., 2022). The postintervention ultrasound imaging was conducted
72 h after the last training session. The CV, SEM, and ICC with 95%
confidence interval among the muscle thickness measurements for
each portion of the lateral thigh were 2%, 0.9 mm, and 0.98 (0.96–
0.99) for the proximal portion; 0.92%, 0.5 mm, and 0.99 (0.98–0.99)
for the middle portion; and 1.45%, 0.6 mm, and 0.99 (0.98–0.99) for
the distal portion.
2.5
|
Training sessions
Training was carried out twice a week for a total of 24 training
sessions. The training sessions were performed at the same time of
the day. Participants were instructed to maintain their habitual di-
etary intake during the training program, and their habitual pre-
workout meal at least 2 h prior to our training sessions. A general and
specific warm‐up, similar to that used in the 1RM testing protocol,
was performed prior to each training session for both groups. Exer-
cises were performed in the following order for all sessions: barbell
squat (front or back according to experimental group), Romanian
deadlift, seated knee flexion, and seated hip abduction. We included
exercises for the lower body posterior chain to avoid possible
dropouts and to maintain the training program as close as possible to
the participants' habitual training routine without influencing adap-
tations in the quadriceps.
The experimental groups performed the training schemes in the
same manner; the only difference between groups was the type of
squat (front vs. back). The participants were instructed to perform
the squat to a parallel depth (e.g., ~100° knee flexion) and to maintain
an external attentional focus during the movement (Coratella, 2022),
either in the FS or the BS group, which was monitored by a certified
strength and conditioning professional. In addition, participants were
instructed to perform the front squat grip in an arm cross grip or
clean grip, according to personal preference, to avoid load and
technique limitations due to reduced shoulder joint flexibility.
The training sessions were performed twice a week, and the
weekly volume for the squat was equally divided between these two
training sessions. The first and second weekly training sessions were
established in a loading zone of 6–‐8 repetitions and 10–12 repeti-
tions, respectively. The posterior chain exercises comprised 2 sets
per exercise using the same repetition and load schemes as in the
squat protocol. Each training session was performed at least 72 h
apart. Table 1provides an overview of the training routine.
Participants were instructed to perform each set at ~2 repeti-
tions in reserve, except for the last set which was performed to
momentary failure. If a participant could not achieve the prescribed
repetition range on a given set, the research supervisor provided
slight assistance on the final 1–‐2 repetitions to achieve the target
zone. The load was adjusted in each set according to ~2 repetitions in
reserve and momentary failure to the specific repetition zone. If the
participant could not achieve the minimum number of repetitions for
the target loading zone or completed the set with ease (e.g., >2
repetitions in reserve), the load was reduced or increased for the
next set, respectively. A 3‐min rest interval was provided between
sets and exercises. Participants were instructed to maintain a repe-
tition tempo of 1s for the concentric action and 2 s for the eccentric
action of each repetition without pausing in transition phases during
the repetitions. All participants were instructed to avoid any addi-
tional moderate‐to‐vigorous lower body exercise during the training
intervention.
The total training volume (TTV) was calculated as follows:
TTV =sets * repetitions * load. We analyzed TTV only for squat
training; the additional exercises (i.e., posterior chain) were not
included in TTV analysis. Importantly, TTV was monitored but not
equated between‐conditions, given that set volume is generally
regarded as the most appropriate gauge for hypertrophy training
(Baz‐Valle et al., 2021; B. Schoenfeld & Grgic, 2017). Moreover, we
employed an individualized approach that considered participants'
previous quadriceps RT volume quantified by the number of sets per
week based on emerging evidence that suggests such a strategy may
optimize muscular adaptations (Aube et al., 2022; Nóbrega
et al., 2022; Scarpelli et al., 2020).
2.6
|
Statistical analysis
Descriptive statistics are expressed as mean �standard deviation (SD).
Data normality and homogeneity of variances were assessed using
Shapiro–Wilk and Levene's test, respectively. After confirming data
normality, an independent t‐test was used to detect possible differ-
ences on each variable at baseline, and a Mann–Whitney test was used
to detect possible differences on TTV and absolute load values be-
tween groups. A 2‐way repeated measures ANOVA was used to
identify possible interactions for dependent variables (muscle strength
and muscle thickness). Weekly set volume was analyzed using an in-
dependent t‐test. An additional interpretation of data was made from
95% confidence intervals (95% CIs) of the mean difference (Mean
diff
)
within‐and between‐conditions. Partial eta squared (
p
n
2
) effect sizes
were calculated and classified as follows: 0.02 small, 0.13 medium, and
0.26 large effect (Bakeman, 2005). The significance level was estab-
lished a priori at p≤0.05. All analyses were carried out in SPSS 25.0
software (IBM SPSS Statistics, IBM Corp, version 25.0).
TABLE 1Training routine throughout 12 weeks.
Exercises Session A Session B
Front squat or back squat ITV �6–8 ITV �10–12
Romanian deadlift 2 �6–8 2 �10–12
Seated knee flexion 2 �6–8 2 �10–12
Seated hip abduction 2 �6–8 2 �10–12
Note: The sets scheme in the front squat or back squat were calculated
according to participants' previous weekly set volume for the
quadriceps and increased by 20% every 4 weeks.
Abbreviation: ITV, Individualized training volume.
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ET AL.

3
|
RESULTS
During the study period, 3 subjects dropped out of the FS group (loss
of interest: n=2; excessive shoulder joint pain due to barbell posi-
tion: n=1) and 2 subjects dropped out of the BS group (injuries not
related to current study: n=1; personal reasons: n=1). Thus, 24
participants (FS =12; BS =12) completed the training intervention.
Table 2shows general characteristics of participants at baseline and
the accumulated TTV between groups. Over the duration of the
training program, the accumulated TTV and the absolute load of BS
were higher than in FS (p=0.033 for both variables) as shown in
Table 2. The average number of weekly sets for squats was statisti-
cally similar between conditions (19.1 �4.1 sets and 21.9 �5.4 sets
for FS and BS, respectively; p=0.171).
Both groups increased their maximum dynamic strength
compared to baseline (F
(1,22)
=78.47; p=0.0001;
p
n
2
=0.78, large
effect); Figure 1(Ho et al., 2019)). A time versus group interaction
was found for the 1‐RM 45° leg press test (F
(1,22)
=10.53;
p=0.0004;
p
n
2
=0.32, large effect) with the BS eliciting greater
muscle strength adaptations compared to the FS (p=0.048;
between‐group Mean
diff
(95% CI) =67.9 kg (0.55–135.2);
p
n
2
=0.16,
medium effect). Within‐group Mean
diff
(95% CI) data are depicted at
Figure 1.
Both groups increased their muscle thickness at the proximal,
middle, and distal regions of the lateral thigh in a similar fashion
(Figure 2). Analysis revealed no time versus group interactions
(F
(1,22)
=0.103; p=0.752;
p
n
2
=0.005, small effect). However, there
was a significant main effect of time for proximal (F
(1,22)
=7.794;
p=0.011;
p
n
2
=0.26, large effect), middle (F
(1,22)
=7.091; p=0.014;
p
n
2
=0.24, medium effect), and distal portions (F
(1,22)
=7.220;
p=0.013; 0.24, medium effect). No between‐group differences were
observed for any muscle thickness region: proximal (p=0.971;
Figure 2A; Mean
diff
(95%CI) =0.10 mm (−5.77 – 5.98);
p
n
2
=0.000,
small effect); middle (p=0.844; Figure 2B; Mean
diff
(95%CI) =0.56 mm
(−5.29 – 6.42);
p
n
2
=0.002, small effect); and distal (p=0.510;
Figure 2C; Mean
diff
(95%CI) =1.39 mm (−2.92 – 5.72);
p
n
2
=0.02, small
effect). Within‐group Mean
diff
(95%CI) data are depicted at Figure 2.
4
|
DISCUSSION
To our knowledge, this is the first paper to compare the effects of the
BS and FS on lower limb strength and hypertrophy adaptations in
healthy females. Our main findings were: (a) BS training promotes
greater dynamic strength‐related improvements in a nonspecific
strength test (i.e., 45° leg press) compared to FS training and (b)
hypertrophic adaptations were similar between conditions among
lateral thigh regions.
In agreement with our initial hypothesis, strength‐related im-
provements varied between conditions with the BS eliciting greater
adaptations (~37.2%) when compared to FS (~19.6%) after a 12‐week
period. Importantly, these differences were assessed in the 45° leg
press, thus indicating that strength adaptations transferred to a
nonspecific strength task. Previous studies that aimed to compare
dynamic strength gains induced by squatting techniques focused on
different depths (full vs. partial range of motion) and movement
tempo (Kubo et al., 2019; Morrissey et al., 1998; Pallarés et al., 2020;
Usui et al., 2016). Collectively, the findings of these studies, which
investigated squat variations in healthy untrained or recreationally
trained individuals over 7‐to 12‐week periods were similar to our
findings related to within‐group dynamic strength gains after our 12‐
week intervention. Given that our study is the first to investigate the
strength‐related changes between the FS versus BS, direct compar-
isons cannot be made between investigations.
TABLE 2Baseline characteristics, resistance training schemes information, and accumulated total training volume data after
intervention.
Variables FS (n=12) BS (n=12) p
Age (years) 22.2 �3.3 23.8 �1.6 0.152
Height (cm) 165.0 �4.3 165.1 �9.2 0.955
Body mass (kg) 62.4 �8.5 66.5 �13.6 0.386
Body fat (%) 19.8 �3.4 19.4 �3.0 0.765
Experience (years) 1.8 �1.1 2.3 �1.5 0.418
1‐RM 45° leg press (kg) 219.5 �93.5 247.5 �84.2 0.450
1‐RM:Body mass ratio (a.u.) 3.4 �1.0 3.7 �1.0 0.511
Previous QTV (sets.week‐1) 13.1 �2.8 15.0 �3.7 0.171
Absolute load (kg) 48.6 �23.7 63.4 �16.9 0.033*
Training volume (sets.week‐1) 19.1 �4.1 21.9 �5.4 0.171
Total training volume (kg) 140087.1 �84358.2 188731.5 �68984.4 0.033*
Note: Data are expressed in mean �SD.
Abbreviations: 1‐RM, one repetition maximum; BS, back squat; cm, centimeters; FS, ront squat; kg, kilograms; QTV, quadriceps training volume.
*significantly difference between‐groups (p≤0.05).
EUROPEAN JOURNAL OF SPORT SCIENCE
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11

Moreover, we employed a nonspecific dynamic strength test in
an exercise that was not employed in the training program. This
decision is consistent with the principle of specificity, since regularly
training with the same exercise used in the strength assessment can
influence the outcome (Mattocks et al., 2017). However, to date,
there are no longitudinal data regarding the effects of the FS versus
BS on a neutral strength test; thus, our study adds novel findings to
the literature related to nonspecific strength testing.
Evidence suggests that biomechanical differences exist between
BS and FS training (B. J. Schoenfeld, 2010). Yavuz and Erdag (2017)
compared to kinematic activities between the BS and FS and found
that the BS has greater hip flexion angles than the FS. Krzyszkowski
and Kipp (2020) found that peak hip extensor net internal joint
moments were higher in BS compared to FS training. These biome-
chanical differences might uniquely influence the activation of hip
extensor muscles during each respective squatting technique,
resulting in differential dynamic strength adaptations. Nevertheless,
it is important to point out that neither discrepancies in TTV between
groups nor individualized volume approaches seem to influence
strength adaptations (Aube et al., 2022; Nóbrega et al., 2022). Similar
to our data, Yavuz and Erdag (2017) showed that participants could
lift greater absolute loads in the BS than the FS, perhaps due to ki-
nematic and kinetic differences (i.e., hip angle) between them. In
addition, it is well‐documented that high loads are a main driver of
muscle strength adaptations (Lopez et al., 2021). Since the BS allows
the use of higher absolute loads compared to the FS, this may have
elicited higher neural adaptations, which may partially explain our
findings. These explanations remain speculative and warrant further
research to provide insight into these hypotheses.
Although both squatting techniques elicited hypertrophic adap-
tations, the changes were similar among lateral thigh regions (pooled
mean increases ~4.4% for back squat and ~5.1% for front squat
training). In contrast to our findings, Usui et al. (2016) compared fast
versus slow movement tempos in the BS at low‐load conditions in
untrained males. After an 8‐week training period, poststudy results
showed an inhomogeneous muscle growth only for the slow move-
ment tempo, with increases observed in the middle and distal vastus
intermedius sites (~6%‐9%) but not in the proximal site (50%, 70%,
and 30% of the femur length, respectively). Alternatively, the fast
movement tempo group showed no significant increases for the
vastus intermedius at any site. Moreover, the vastus lateralis muscle
thickness (analyzed only at 50% of the femur length) showed no
poststudy statistical change for both squat variations. The relative
increases found by Usui et al. (2016) were slightly higher to our
relative increases, which may be attributed to differences in training
status and movement tempos between studies. In addition, it is well‐
established that training volume plays a key role in muscle plasticity
(B. J. Schoenfeld et al., 2017), and although TTV was not equated
between conditions, we ensured an individualized progressive RT
volume. The muscle thickness responses in all portions of the lateral
thigh were similar between conditions, which is consistent with
previous studies despite not equalizing the TTV (Barcelos et al., 2018;
B. J. Schoenfeld et al., 2015).
Emerging evidence has shown that variation in exercise selection
can influence nonuniform skeletal muscle adaptations (Kassiano
et al., 2022; Zabaleta‐Korta et al., 2020). Previous studies that
investigated interventions with squat training on regional hypertro-
phy among quadriceps muscles found similar increases between
proximal to distal portions, similar to our findings (Kojic et al., 2022;
Merrigan et al., 2019). It should also be noted that the BS may not
optimize hypertrophy of all the quadriceps heads. Fonseca
et al. (2014) found that a combination of different lower body ex-
ercises promoted more uniform development of the quadriceps
compared to the BS alone, which showed inferior hypertrophy in the
vastus medialis and rectus femoris in a cohort of untrained young
men over a 12‐week period. Similarly, Kubo et al. (2019) found that
the BS preferentially hypertrophied the vasti muscles, with no
appreciable effect on the rectus femoris in a cohort of untrained
young men over a 10‐week interventional period. Our study only
assessed the lateral quadriceps, and thus we cannot draw conclu-
sions on this topic. However, our data indicate that both FS and BS
elicited a sufficient training stimulus to promote growth along the
length of the lateral thigh, specifically to the vastus lateralis and
intermedius.
The present study is not without limitations. First, our findings
are specific to recreationally trained females and should not be
extrapolated to other populations, such as strength‐oriented ath-
letes, males, or older individuals. Second, although we attempted to
verbally encourage participants to reach momentary failure in the
last set, some participants volitionally terminated the set prior to
failure due to discomfort with the barbell position. Additionally,
failure in the barbell squat can arise from the fatigue of other muscle
groups, not necessarily the quadriceps femoris, due to biomechanical
characteristics of the exercise. Although we cannot rule out that this
occurrence may have influenced results, the literature indicates that
training to failure is not obligatory for muscle adaptations (Grgic
et al., 2021), and thus confounding from this variable appears un-
likely. Third, in addition to reports of shoulder discomfort due to the
FS positioning, we did not consider previous experiences with the FS
as a requirement for eligibility in our study, which may have
confounded results. Fourth, we used a dynamic strength test and only
assessed muscle thickness, a one‐dimensional imaging modality, of
the vastus lateralis and vastus intermedius. Thus, results may be
different when assessing strength with isometric testing or employ-
ing two‐or three‐dimensional imaging measures, such as cross‐
sectional area or muscle volume in other lower limb muscles, such
as the vastus medialis and recuts femoris. Fifth, although the par-
ticipants were instructed to maintain their habitual dietary intake
during the training program, we did not directly control this variable
and thus cannot rule out the possibility that differences in nutritional
consumption may have influenced results. Sixth, we cannot extrap-
olate conclusions to programs that equalize TTV between conditions.
Finally, we did not account for the dosage of ethynil‐estradiol and
other associated factors of contraceptive pills pharmacokinetics,
which conceivably may have influenced the response to resistance
training.
12
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ENES
ET AL.

5
|
CONCLUSIONS
Our findings suggest that BS training elicits greater lower limb dy-
namic strength on a nonspecific strength test (1‐RM 45° leg press)
than FS training in recreationally trained females; however, both
variations elicit similar hypertrophy adaptations among proximal,
middle, and distal portions of the lateral thigh. Accordingly, coaches
and practitioners who seek to maximize lower limb strength gains on
a nonspecific strength test may benefit from including the BS in their
training routine. In addition, squat variations can be used in a training
block designed to promote homogeneous lateral thigh hypertrophy.
Additionally, if a specific training block does not allow for a high
training volume or the practitioner is unable to use higher loads, the
FS promotes similar hypertrophy in the lateral thigh as in the BS,
even with a lower total training volume and lower absolute loads.
ACKNOWLEDGMENTS
The authors thank the volunteers' effort during the intervention and
to Coordination for the Improvement of Higher Education Personnel
(CAPES – Finance Code 001) for their respective scholarships.
CONFLICT OF INTEREST STATEMENT
BJS serves on the scientific advisory board of Tonal Corporation, a
manufacturer of exercise equipment. The other authors declare that
they have no potential conflict of interest.
ORCID
Alysson Enes
https://orcid.org/0000-0002-8848-7946
Gustavo Oneda https://orcid.org/0000-0001-6046-1691
Danilo Fonseca Leonel https://orcid.org/0000-0001-7483-0937
Guillermo Escalante https://orcid.org/0000-0001-9653-4661
Brad J. Schoenfeld https://orcid.org/0000-0003-4979-5783
Tácito P. Souza‐Junior https://orcid.org/0000-0001-5147-7384
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