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Isokinetics and Exercise Science -1 (2019) 1–8 1
DOI 10.3233/IES-193142
IOS Press
A comparison of muscle electromyographic
activity during different angles of the back
and front squat
Thiago Barbosa Trindadea,b, Jason Azevedo de Medeirosb, Paulo Moreira Silva Dantasc,
Leônidas de Oliveira Netod, Daniel Schwadec, Wouber Hérickson de Brito Vieiraeand
Filipe Fernandes Oliveira Dantasb,∗
aDepartment of Physical Education, Catholic University of Brasilia, Brasilia, Brazil
bDepartment of Physical Education, University Center of Rio Grande do Norte, Natal, Brazil
cDepartment of Physical Education, Federal University of Rio Grande do Norte, Natal, Brazil
dDepartment of Arts, Federal University of Rio Grande do Norte, Natal, Brazil
eDepartment of Physical Therapy, Federal University of Rio Grande do Norte, Natal, Brazil
Received 2 April 2019
Accepted 2 May 2019
Abstract.
BACKGROUND: Many different squatting techniques have been recommended, but few studies tried to identify how different
muscle groups contributed to this movement in each technique.
OBJECTIVE: To compare the electromyographic activation (EMG) of the thigh, hip and trunk muscles during maximal volun-
tary isometric contractions in the back and front squat performed in different degrees of knee flexion, while also comparing the
levels of force produced during different ranges of motion.
METHODS: Ten healthy men (30.7 ±7.9 years), regularly practicing strength training, performed maximal isometric actions
during back and front squats, at 60◦, 90◦and 120◦degrees of knee flexion. The electromyographic activity of the rectus femoris,
vastus lateralis, vastus medialis, biceps femoris, gluteus maximus, and erector spinae was recorded.
RESULTS: At 60◦a lower EMG activation in both squats was observed although this depth showed the highest levels of max-
imal voluntary isometric strength. Increasing knee flexion to 120◦did not result in greater muscle activation. Only at 90◦there
was no significant difference in EMG activity between the front and back squat.
CONCLUSIONS: A greater squat depth did promote a decrease in EMG activity When executed in isometric contraction, paral-
lel squatting offers better ratio of force X recruitment of primary motor muscles. Therefore, this amplitude can be used in training
or rehabilitation strategies, both in frontal and posterior variations (with higher level of strength), observed the most convenient
option for the practitioner.
Keywords: Electromyography, strength training, muscles, squat
∗Corresponding author: Filipe Fernandes Oliveira Dantas, En-
dereço: Avenida das Alagoas, N 300, APT 401 B, CEP: 59086-
200; Bairro Neópolis, Natal-RN, Brazil. E-mail: filipepersonal@
hotmail.com.
1. Introduction 1
Despite its complex execution, the squat is regarded 2
as one of the best exercises in strength training, since 3
it allows the recruitment of various muscle segments 4
in one single motion [1] For this reason, it is one of 5
the most used multi-joint exercises in strength training 6
ISSN 0959-3020/19/$35.00 c
2019 – IOS Press and the authors. All rights reserved
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2T.B. Trindade et al. / A comparison of muscle EMG activity during different angles of the back and front squat
protocols, both by recreational practitioners and ath-7
letes [2–4] The complexity of the squat, together with8
its many variables related to performance, demand the9
understanding of its biomechanics [5] in order to allow10
ideal muscle development while minimizing the risk of11
injuries due to poor form [6]. Among the many differ-12
ent squatting techniques, both the back squat (BS, per-13
formed with a barbell resting on the shoulders, over the14
trapezius, slightly above the posterior deltoid), and the15
front squat (FS, performed with a barbell resting on the16
anterior deltoids and clavicles, sustained with the help17
of both arms), have been recommended [4,7].18
Both variations provide important activation of the19
torso and lower limb muscles. However, the differ-20
ences in technique also create differences in muscle21
recruitment, which still need to be investigated [8,9].22
Gullett et al. [8] and Contreras et al. [10] found no sig-23
nificant differences between FS and BS exercises re-24
garding hip and thigh muscle activation. The first study25
analyzed two sets of three repetitions at 70% of 1 rep-26
etition maximum (1RM), while Contreras et al. [10]27
found no statistical differences in muscle activity be-28
tween the two variants (both parallel and full range of29
motion) with a 10RM load in healthy women. On the30
other hand, Yavuz et al. [9] reported higher muscle ac-31
tivity in the vastus medialis in the FS when compared32
to the back squat, as well as greater muscle activity in33
the erector spinae when trained males performed BS34
using a 1RM load. Korak et al. [11] reported higher35
muscle activity during the FS (M =94%, SD =15%)36
compared to the deadlift and BS during 3 repetitions at37
75% 1RM load.38
To better understand the biomechanical aspects of39
these exercises, a number of studies have aimed to40
analyze the effects of different squat depths, in order41
to identify how different muscle groups contribute to42
perform this motion [12]. For instance, some have re-43
ported that the gluteus maximus muscle shows higher44
activation when squatting with higher degrees of knee45
flexion [13,14]. Regarding other muscles, Jaberzadeh46
et al. [15] showed that the ratio of the EMG activity be-47
tween the vastus medialis oblique and the vastus later-48
alis was higher when performing deeper squats. How-49
ever, since these studies only addressed the BS, we50
cannot infer that the same would be observed when51
performing the FS.52
The relationship between muscle activation level53
and the force generated in different types of squats54
seems to vary as a function of the angular relation-55
ships of the joints involved – specially the hip, knee 56
and ankle – as well as the position of the torso [16]. 57
In this sense, some studies reported that higher loads 58
can be lifted during the BS when compared to the 59
FS [8,9]. This may be due to higher tibiofemoral com- 60
pressive forces and a bigger moment arm of the ex- 61
tensor muscles [8]. These differences may also be re- 62
lated to variables interfering in the relationship be- 63
tween electromyographic activation and strength, such 64
as angular and contraction velocity [17]. 65
In general, most of the studies that compared EMG 66
activity and the amount of force generated between dif- 67
ferent types of squats did so during dynamic actions. 68
However, a more concrete association between these 69
measures can be obtained during maximal isometric 70
actions, since there is an increase in the firing rate of 71
motor units in this type of muscle action, even when 72
their recruitment reaches a saturation, causing the mus- 73
cle to keep producing energy for the EMG signal lead- 74
ing, in turn, to an increase in amplitude [17]. 75
Moreover, when considering the mutual interference 76
between the range of motion of the different types 77
of squat, muscle activation and the force produced in 78
maximal isometric actions, there is a lack of sufficient 79
evidence for clarifying the relationship between these 80
variables. Additionally, different angles of exercise in- 81
fluence the inclination angle of the trunk and, conse- 82
quently, muscle recruitment during squatting. Such in- 83
formation may play a large role in the prescription of 84
these exercises in strength training programs and in 85
understanding lower body muscle activation patterns 86
between squat variations. These are important factors 87
in strength and conditioning for isolating or creating 88
greater activation of selected lower body muscles for 89
training, performance increases, injury prevention, or 90
rehabilitation techniques. 91
Therefore, the aim of our study was to compare the 92
EMG activation of the muscles of the thigh, hip and 93
torso during maximal isometric contractions in both 94
BS and FS, performed at different degrees of knee flex- 95
ion. Our hypothesis was that in both kinds of squats the 96
lower the degree of knee flexion, the higher the level of 97
muscle activation, mainly in the posterior hip and thigh 98
muscles. We also believe that the strength of the triple 99
ankle, knee and hip extension would be inversely pro- 100
portional to the yours flexion angle and will be higher 101
during the higher degrees of knee flexion, particularly 102
in the BS. Furthermore, we hypothesized, due to previ- 103
ous findings, that the FS would produce greater muscle 104
activity of the GM. 105
Muscle EMG activity during back and front squat
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T.B. Trindade et al. / A comparison of muscle EMG activity during different angles of the back and front squat 3
2. Methods106
2.1. Subjects107
The participants were 10 healthy men (30.7 ±108
7.9 years old; 1.74 ±0.08 cm height; 85.2 ±13.7 Kg109
of body weight; 27.9 ±1.9 Kg/m2BMI, and 13.1 ±110
8.1 years of training), right side dominant, who had at111
least one year of weekly practice of both BS and FS112
in their strength training programs. None of the par-113
ticipants presented any musculoskeletal injuries that114
could limit their ability to perform the procedures and115
squat techniques described ahead. Before the begin-116
ning of the study, each participant provided written in-117
formed consent elaborated according to the recorded118
standards of the 466/12 resolution (CONEP), approved119
by the Ethics Committee of the North Riograndense120
League against Cancer (Proponent institution: League121
of Teaching of Rio Grande do Norte, CPAE protocol:122
39327414.5.0000.5293).123
2.2. Design124
In this cross-over trial, subjects performed three ex-125
perimental sessions with a washout period of 48 hours.126
In the first session, subjects performed a maximum vol-127
untary isometric contraction (MVIC) test, from which128
we verified the signals corresponding to the root mean129
square (RMS) peaks regarding each evaluated muscle130
using isolated exercises, with the goal being to estab-131
lish parameters for posterior normalization. Still in the132
first session, subjects went through a familiarization133
with the tools and equipment that would be posteriorly134
utilized in the FS and BS sessions, both which were135
assessed through the maximal isometric contraction.136
In the second and third sessions, subjects performed137
the FS and BS, in random order. Subjects rested for138
five minutes before all maximal isometric actions, with139
the order also being random for the 60◦, 90◦and 120◦
140
angles of knee flexion. We stimulated the subjects to-141
wards performing the maximum possible force in the142
triple extension of knee, ankle and hip, in both kinds of143
squats and in all three degrees of depth.144
2.3. Procedures for recording the EMG signals145
To measure the MVIC, we fixed surface electrodes146
on the right side of the body above the muscle belly147
of the following muscles: rectus femoris (RF), vastus148
lateralis (VL), vastus medialis (VM), biceps femoris149
(BF), gluteus maximus (GM) and erector spinae (ES).150
The electrodes were placed according to Broer and 151
Houtz [18]. 152
To verify the relative RMS value for each of the 153
assessed muscles, subjects were oriented to perform 154
MVIC during knee extension limited to 60◦(for the 155
VL, VM and RF muscles); during knee flexion lim- 156
ited to 60◦(for the BF muscle); during hip extension 157
limited to 20◦(for the GM muscle); and during back 158
extension, starting from the ventral decubitus position 159
(for the ES muscles). Still in the first session, subjects 160
underwent familiarization with the FS and BS in the 161
following degrees of knee flexion: 60◦; 90◦and 120◦162
(angles were adjusted using a manual goniometer). 163
During both squat variations, knee flexion was limited 164
using two chains fixed to the floor, both of which were 165
coupled with a load cell, in both far ends of the barbell, 166
in order to assess the level of force generated in each 167
angle of knee flexion (Fig. 1). During the FS, the bar- 168
bell was positioned on the anterior deltoids and clavi- 169
cle while during the BS, the barbell was positioned on 170
the trapezium, slightly above the posterior deltoids. 171
2.4. Acquisition of the EMG signal and maximum 172
isometric force 173
The EMG signal and maximum isometric force 174
recordings started at the same time, following a verbal 175
command issued by the researcher. Participants were 176
requested to perform a 10-second MVIC for every an- 177
gle of knee flexion. We selected the 5 seconds cor- 178
responding to the period where the highest force was 179
employed over the load cells (±2.5 seconds starting 180
from peak) and analyzed the EMG signals generated 181
throughout this period. We then calculated the mean 182
value of the rectified signal referring to the RMS, con- 183
sidering values obtained from those 5 seconds of max- 184
imum contraction. The signals were obtained from the 185
right lower limb only. 186
To assess the maximum isometric force generated by 187
subjects in both squat variations, we utilized two free 188
load cells (Miotec R
, Porto Alegre/RS, Brasil), each 189
one having a nominal capacity of 200 Kgf. With the 190
use of chains, we coupled a load cell between each end 191
of the barbell and the ground, thus forming 90◦angles 192
between the barbell and the dynamometer and between 193
the chains and the ground as to provide more freedom 194
to the subjects during the handling of the attachments 195
(Fig. 1). 196
2.5. EMG data 197
Six pairs of Ag/AgCl surface electrodes, model 198
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4T.B. Trindade et al. / A comparison of muscle EMG activity during different angles of the back and front squat
Fig. 1. Positioning of the barbell and adjustment of the angles of knee flexion during the front and back squats. A – Front squat at 60◦of knee
flexion; B – Front squat at 90◦of knee flexion; C – Front squat at 120◦of knee flexion ; D – Back squat at 60◦of knee flexion; E – Back squat
at 90◦of knee flexion; F – Back squat at 120◦of knee flexion. The circle and the square presented in Panel A represent, respectively, the load
cell and the chains fixed to the floor with the help of a carabiner.
2223BRQ, 3 M brand, were fixed by the same re-199
searcher (avoiding possible inter-rater variability) over200
the bellies of all muscles, parallel to the muscle stri-201
ations of the respective muscle fibers, after previous202
cleansing and trichotomy of skin surface. The proce-203
dure of electrode fixation and positioning followed the204
same criteria adopted in the first session, where sub-205
jects performed the MVIC tests. A distance of 2 cm be-206
tween the centers of electrodes was kept. We assessed207
muscle activation utilizing an 8-channel electromyo-208
graph Miotool (Miotec R
, Porto Alegre/RS, Brasil)209
with 1000 Hz sampling rate, 2000 times gain settings210
and bipolar surface electrodes. Data analysis was per-211
formed using an integrated Miograph 2.0 software;212
with a 60 Hz notch filter, 20 Hz high-pass filter and213
500 Hz low-pass filter. Two of the channels were con-214
nected to the load cells, and the remainder were used215
to assess the EMG activity of the chosen muscles.216
2.6. Statistical analysis217
Data were typed originally in the database of the218
SPSS R
(Statistical Package for Social Sciences) soft-219
ware, version 21.0, for Windows. Through the Shapiro-220
Wilk test, we verified that data did not present nor- 221
mal distribution. Thus, we compared EMG activity 222
(RMS) and the amount of isometric force generated 223
in the different ranges of motion of both squats us- 224
ing the Friedman test. Whenever significant differences 225
were found between values, we proceeded to compare 226
them through paired measures (Wilcoxon test) using 227
the Bonferroni correction. The Wilcoxon test was ap- 228
plied when comparing the EMG activation of each as- 229
sessed muscle, as well as the force generated in the dif- 230
ferent squat variations. In every analysis, a significance 231
level lower than 5% (p < 0.05) was taken into account. 232
3. Results 233
A larger magnitude of force was produced in the 234
BS, in all assessed angles (Fig. 2). We verified that 235
the maximum voluntary isometric force decreased pro- 236
gressively as the degree of knee flexion increased. 237
Figure 2 shows results related to the isometric force 238
producted. 239
The results of the comparison of muscle activity be- 240
tween the FS and the BS are shown in Fig. 3. At 60◦241
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T.B. Trindade et al. / A comparison of muscle EMG activity during different angles of the back and front squat 5
Table 1
Electromyographic activity referring to the percent of maximum voluntary isometric contraction (%MVIC) for the front and back squats in
different angles of knee flexion
Front squat Back squat
60 degrees 90 degrees 120 degrees 60 degrees 90 degrees 120 degrees
Md
(Q25–q75 )
Md
(Q25–q75 )
Md
(Q25–q75 )
pMd
(Q25–q75 )
Md
(Q25–q75 )
Md
(Q25–q75 )
p
GM 21.2
(14.5–36.1)
47.1
(19.6–64.3)*
29.9
(17.0–45.0)
0.001 33.2
(18.2–68.2)
58.7
(35.8–77.3)*†
35.1
(17.7–42.9)
0.020
ES 34.4
(28.3–43.5)
47.1
(35.6–63.0)*
55.0
(38.5–68.9)*
0.013 34.4
(26.8–44.4)
57.2
(37.5–74.5)*
56.9
(28.7–67.5)
0.004
BF 5.3
(4.5–12.3)
9.5
(7.7–20.9)*
14.8
(10.0–21.7)*
0.002 15.6
(7.4–20.8)
15.2
(9.3–26.0)
12.9
(10.7–20.1)
0.407
RF 25.4
(17.7–32.3)
42.4
(32.4–57.0)*
41.7
(30.9–61.4)*
0.007 23.4
(20.7–37.7)
45.3
(38.5–71.6)
57.4
(36.6–82.5)
0.006
VL 33.8
(19.8–49.4)
58.1
(42.5–70.2)*
44.3
(34.3–65.3)*
0.003 40.6
(30.7–82.9)
65.7
(50.2–115.2)*
65.5
(46.5–123.8)*
0.001
VM 37.5
(30.9–47.0)
58.9
(31.2–90.8)
48.3
(30.6–85.5)
0.407 42.6
(22.3–80.1)
66.1
(43.5–119.0)
64.2
(44.9–121.0)
0.067
GM =gluteus maximus; ES =erector spinae; BF =biceps femoris; RF =rectus femoris; VL =vastus lateralis; VM =vastus medialis; Md =
median; Q25–Q75 =interquartile range; p(friedman); *Significant difference at the 60◦angle; †Significant difference at the 120◦angle.
Fig. 2. Isometric force production between the squat variations at
different degrees of knee flexion. KGF – Kilograms force. Values are
shown in median and interquartile range. *Significant difference be-
tween squat variations; †Significant difference at 90◦of knee flex-
ion; ‡Significant difference at 120◦of knee flexion.
of knee flexion, the GM, BF and VL had a higher ac-242
tivation during the FS. At 120◦, only the RF and the243
VL had a higher activation during the FS. At 90◦, there244
was no significant difference between muscle activa-245
tion during the FS and the BS.246
Table 1 outlines the normalized values of the EMG247
signals between the different angles. The gluteus max-248
imus had a higher activation when knee flexion was at249
90◦, particularly during the FS. The erector spinae pre-250
sented a higher activation at 90◦and 120◦during the251
FS, while in the BS the highest activation was observed252
at 90◦. Both the biceps femoris and the rectus femoris253
were more activated at 90◦and 120◦during the FS.254
However there were no significant differences between255
angles during the BS. The vastus lateralis was more ac-256
tivated at 90◦and 120◦, in both squats. Finally, the vas-257
tus medialis was the only muscle which did not show258
any difference in activation between different angles or 259
squat variations. 260
4. Discussion 261
Our results indicate that, in both the FS and BS, the 262
lowest electrical activity of the assessed muscles was 263
observed when the knee was flexed at 60◦. However, 264
the highest levels of isometric force were obtained at 265
this range, as we had previously hypothesized. Despite 266
this, our hypothesis as a whole was only partially con- 267
firmed since the increase in the range of knee flexion to 268
120◦did not result in a larger activation of the assessed 269
musculature. Only in the 90◦range no significant dif- 270
ference in muscle activation between BS and FS were 271
observed. 272
Mechanical conditions, as opposed to neural ones, 273
have a much bigger influence on the reduction elec- 274
trical activity of the assessed muscles observed during 275
knee flexion at 60◦. At this range, the rotatory compo- 276
nents show a possible decrease, as well as an increase 277
in the participation of translatory components of com- 278
pression in triple knee extension (knee, ankle and hip) 279
when compared to other ranges of motion of this exer- 280
cise. On the other hand, the increase in maximum iso- 281
metric strength, also observed at 60◦of knee flexion 282
may be explained by the increase in moment. In this 283
angle, the resistance moment is lower in the triple knee 284
extension, when compared to the 90◦and 120◦angles, 285
due to a shorter resistance arm – a lower perpendicular 286
distance between the weight (fixed bar) and the rota- 287
tion axis of the involved joints [19]. 288
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6T.B. Trindade et al. / A comparison of muscle EMG activity during different angles of the back and front squat
Fig. 3. Mean values of muscle activity of different muscles during back and front squats, represented by the percentage of maximal voluntary
isometric contraction (%MCIV). A – 120◦of knee flexion; B – 90◦of knee flexion; C – 60◦of knee flexion; GM =gluteus maximus; ES
=erector spinae; BF =biceps femoris; RF =rectus femoris; VL =vastus lateralis; VM =vastus medialis. Values are shown as median and
interquartile range. *Significant difference between squat variations.
Despite the lack of a kinematic analysis in our study,289
it is possible to affirm that squatting with knees flexed290
at 60◦, in both variations, demanded lower degrees291
of hip and ankle flexion, thus reducing moment over292
the requested segments, even during an increase in the293
maximum force generated in this range. In these con-294
ditions, we observed a higher capacity to support axial295
load at the expense of a lower activation of the knee,296
hip and torso extensors, similar to Yavuz et al. [9]. This297
relationship may make it undesirable to perform squats298
in ranges of motion equivalent to 60◦of knee flexion,299
since the increase in load may promote a linear in-300
crease in the compression of the body of the vertebrae301
as well as intradiscal compression [19].302
The similarity in activation of the assessed muscles303
during MVIC at 90◦of knee flexion, in both squat304
variations, supports previous findings obtained through305
EMG analysis during dynamic exercise [8,9]. Lower306
loads can be used in the front squat in order to pro-307
mote equivalent muscle activation levels compared to308
those obtained during the BS. When considering this309
premise, we speculate that the front squat may be a safe310
and efficient alternative for the recruitment of thigh,311
hip and torso muscles, resulting in lower overloads 312
for the joints involved in this motion. During the back 313
squat, considering all three ranges of motion, the glu- 314
teus maximus muscle showed higher EMG activation 315
when the knee was flexed at 90◦. This can be justified 316
by the optimal length-tension relationship obtained for 317
this muscle during this circumstance [10]. 318
Our findings do not match those obtained in a pre- 319
vious study [13] which had indicated a direct relation- 320
ship between gluteus maximus activation and the depth 321
of the dynamic squat. We suggest that this finding 322
was due to the utilization of submaximal loads, a fact 323
that may have altered the recruitment pattern of high 324
threshold motor units, especially in more experienced 325
individuals [9]. In lower load conditions, stronger mus- 326
cles may compensate the activation of weaker ones, 327
promoting variations in their respective EMG activi- 328
ties, which can compromise the results found. Further- 329
more, in this study the loads were not balanced for 330
comparison of deep and partial squats, which might 331
have compromised the results. 332
The rectus femoris has manifested lower EMG ac- 333
tivation in all variations and ranges of motion when 334
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T.B. Trindade et al. / A comparison of muscle EMG activity during different angles of the back and front squat 7
compared to the other muscles of the quadriceps – the335
vastus lateralis and vastus medialis. This may be due336
to a possible stabilization of its length, since its mu-337
tual function as a knee extensor and hip flexor pro-338
motes a simultaneous shortening of one of its ends339
while stretching the other [5,7,9]. Regarding the low340
activation of the biceps femoris in all assessed ranges341
and variations, we suggest that the squat may not be342
the best exercise option for the work of the hamstring343
muscles, as proposed by Contreras et al. [10] and Gul-344
lett et al. [8]. In this context, Ebben et al. [20] indicated345
that knee flexion exercises and the stiff-legged deadlift346
(performed with both knees fully extended) might be347
better options.348
One of the more significant clinical implications of349
the current results lies in the relationship between lifted350
load and muscle activation. Considering that the use of351
lower loads when performing the front squat did not352
generate a decrease in the activation of the targeted353
muscles this variation may be safer and better suited354
for practitioners who want to prioritize the preserva-355
tion of joints that have a potential to be vulnerable to356
external load.357
The main limitation of our study is due to the man-358
ner through which we performed the analysis. All359
squat exercises were performed as maximal isomet-360
ric contractions, which reduces the similarity of the361
tests we analyzed with the practices observed in gyms362
and training centers, where squats are commonly per-363
formed as dynamic exercise. Additionally, the normal-364
ization of the EMG signals from MVIC obtained in365
various angles and variations may have interfered with366
our results, despite the existing precedents in litera-367
ture [4]. The normalization obtained through own max-368
imal isometric contractions, performed during the ex-369
ecution of the assessed squats, might have provided370
more reliable parameters for the assessment of the pro-371
posed variables. Lastly, anthropometric and kinematic372
differences between sexes exist, so future research is373
needed to fill in this gap [21].374
5. Conclusion375
Our results indicate that in both the front and back376
squats, muscle activation was lower at 60◦of knee377
flexion, despite the highest force production being ob-378
tained during this range. Furthermore, an increase in379
range to 120◦did not result in a higher EMG activity of380
the assessed muscles. Regarding comparisons between381
the front and back squat, we observed that the front382
squat demands the use of lower loads in order to pro- 383
mote levels of similar muscle activation to those ob- 384
tained during the back squat. This is a practical con- 385
clusion as far as strength and conditioning profession- 386
als, trainers, and therapists who want to increase per- 387
formance without increasing the load during squatting, 388
are concerned. 389
Conflict of interest 390
The authors of this study declare no conflicts of in- 391
terest. 392
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