Surface Electromyography Analysis of the Free, Smith and Split Squats Performed by Strength Trained Males

Abstract

Introduction: Squats recruit a large proportion of the body’s muscular system and provide a foundation for strength training programs for athletes. However, our understanding of electromyographical activity in variations of the high-bar back-squat, notably the split squat, is limited. Therefore, this study aimed to investigate surface electromyography (EMG) in the free, Smith and split types of squat.
Method: A randomised sample of 10 healthy strength-trained males (mean ± SD age, 20.3 ± 0.5 years;height, 1.7 ± 0.6 m; mass, 78.1 ± 9.5 kg; strength training, 2.5 ± 0.5 years) performed 3 repetitions of each type of squat at 75% of their one repetition maximum. A Noraxon EMG - Raxon system was used to collect peak EMG, root-mean-square EMG (RMS EMG), and integrated EMG (iEMG) data for the eccentric and concentric phases of the squat. EMG data from the free and split squats were normalised to the Smith squat. Two-way ANOVAs were used for the analysis of type-of-squat and phase-of-squat (p ≤ 0.01).Results: Statistically significant effects for type-of-squat were found for peak EMG and iEMG of the bicep femoris (BF), lateral gastrocnemius (LG) and tibialis anterior (0.001 ≤ p ≤ 0.003), and for RMS EMG of the BF(p = 0.002) and LG (p = 0.001). Significant differences in phase-of-squat were found for peak EMG and RMS EMG of BF (p = 0.001).
Discussion: The split squat elicited higher BF and LG muscle activity compared to the free and Smith squats. The findings suggest that the split squat effectively stimulates the BF and LG muscles and should consequently form an integral part of strength programs for athletes.

Full text

Volume 5, Issue 3, December 2016 | JOURNAL OF FITNESS RESEARCH 68
ISSN 2201-5655 © 2016, Australian Institute of Fitness
ORIGINAL RESEARCH
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Volume 5, Issue 3, December 2016 | JOURNAL OF FITNESS RESEARCH 69
INTRODUCTION
The barbell back squat provides a functional
transfer into numerous sporting movements and it is
the predominant exercise in strength programs 1
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bilateral barbell squat in developing maximal strength
and power of the lower extremities in athletes 2-5
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speed and acceleration in sprinting, and performance
in countermovement jumps 6-97KHOLWHUDWXUH
contains extensive research on squat depth, foot
placement, and muscle activation in the two-legged
squat 10; however, the biomechanics of the split squat
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squat movement to a straight-line translatory motion
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E\6FKZDQEHFNet al12 evaluated the discrepancies in
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proximal attachment crosses the knee joint, and both
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movements such as the free squat 127KHOLWHUDWXUH
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stabilise the ankle, knee and hip joints in the free
squat, and that the free squat is more advantageous
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perform squats is that less experience in strength
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strength and power have been achieved through the
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opinion amongst strength and conditioning coaches
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been suggested that because the motion of the
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straight line it may increase the risk of injury as this
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be attributed to methodological differences in squat
technique, stance width, squat depth, and foot
positioning 12,15)RUH[DPSOH3DROLet al16 found that
a wide stance elicits a greater recruitment of the
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recruitment is related to barbell positioning 17,QWKH
high-bar back squat the barbell is placed on top of
the trapezius muscles, whereas in the low-bar back
squat the bar is positioned lower on the back just
above the spine of the scapula and immediately
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the athlete to adopt a more upright trunk posture
which elicits a greater contribution from the
quadriceps 17,QWKHORZEDUWHFKQLTXHWKHWRUVRLV
bent further forward in order to keep the bar over
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hamstrings and gluteus more intensely and usually
allows lifting heavier weights, therefore setting
appropriate conditions to develop greater muscular
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place an emphasis on bilateral squatting, however
athletes perform many sporting movements
unilaterally 18,19 5HVHDUFKKDVVKRZQWKDWXQLODWHUDO
exercises increase stimulation of the neuromuscular
system to stabilise the musculature of the trunk and
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and control in the athlete, often causing a reduction
of lifted loads and power output during strength
training 207KXVWKHUHLVGLVDJUHHPHQWDPRQJVW
strength and conditioning coaches regarding the
importance of bilateral and unilateral exercises to

Volume 5, Issue 3, December 2016 | JOURNAL OF FITNESS RESEARCH 70
LPSURYHDWKOHWLFSHUIRUPDQFH6DHWHUEDNNHQDQG
)LPODQG21 explained that the split squat helps
develop the lateral subsystem, described as the
frontal plane stabilisation provided by the lumbo-
pelvic-hip muscle complex responsible for
transferring force between the lower and upper body
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muscles engaged in the lateral subsystem include the
gluteus medius, hip adductors and quadratus
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performing unilateral exercises 223UHYLRXVUHVHDUFK
suggests that unilateral training such as the split squat
stimulates the lateral subsystem musculature and may
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elevated split squats, and split squats has been
SUHYLRXVO\LQYHVWLJDWHGE\GH)RUHVWet al237KH
muscles studied included the gluteus maximus%)
semitendinosus, rectus femoris, vastus lateralis
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muscle showed considerably higher activation in the
free squat than in the split squat during the
concentric phase of the exercise with a mean
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FRQGXFWHGE\/RQJSUHet al24 found that the
quadriceps yields higher activation in the lunge
exercise compared to the free squat in healthy young
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different types of squat may assist in designing
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reduce antagonistic muscular imbalances and injury
risk in athletes 8,14
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signal which represents a measure of the maximal
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level of the physiological activity in the motor unit
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provide practical information for coaches and
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and co-activation characteristics of lower-limb
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METHODS
Experimental Design
This study consisted of an experimental repeated
measures design using strength trained males chosen
at random in which the participants performed one
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squats at a parallel depth using a load of 75% of the
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SHUIRUPDVLQJOHUHS,I WKHODWWHUDWWHPSWLV
successful, then rest for 3-5 mins and continue
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performance of squat type was randomised to
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DFWLYDWLRQSDWWHUQV7KHGHSHQGHQWYDULDEOHZDV
muscle EMG activity7KHLQGHSHQGHQWYDULDEOHV
included type-of-squat and phase-of-squat([WUDQHRXV
variables encompassed cross-talk, individual variations
in posture when lifting, and unrelated voluntary
contractions 256WDQGDUGLVHGVTXDWLQVWUXFWLRQVZHUH
implemented 27

Volume 5, Issue 3, December 2016 | JOURNAL OF FITNESS RESEARCH 71
Participants
7HQKHDOWK\VWUHQJWKWUDLQHGPDOHVRI PHDQ6'
DJHRI \HDUVKHLJKWRI PDQG
PDVVRI NJSDUWLFLSDWHGLQWKHVWXG\7KH
participants were three 100m sprinters, three rugby
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The participants trained for their sport two times per
week and were experienced in using a variety of
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injury at the time of testing and had no history of
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to data collection the participants did not take part in
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muscles were fully recovered from previous training
sessions and prevented delayed onset of muscle
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technique 285LVNDVVHVVPHQWVZHUHHYDOXDWHGSULRU
to data collection and all participants provided
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Electromyography Procedures
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9/2%)/*DQG7$ZKLFKDUHWKHSUHGRPLQDQW
muscles in the execution of squats 273UHSDUDWLRQRI 
the skin overlying the muscle sites was carried out by
cleaning the skin with alcohol wipes, shaving with a
razor and lightly abrading the skin with sand paper 25
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attached to the skin overlying the centre of the belly
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electrodes was as follows 29 
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the line between the anterior spina iliaca superior and
the joint space in front of the anterior border of the
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to the line between the anterior superior iliac spine
and the joint space in front of the anterior border of
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line from the anterior superior iliac spine to the
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line between the ischial tuberosity and the lateral
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of the line between the ischial tuberosity and the
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The muscles of the right leg were analysed in all
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electrode recording sites secured with double sided
tape to prevent the short wires from moving and
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(0*VLJQDOYLD:L)LWKH(0*V\VWHPLQLWLDOO\
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were analysed using the manufacturer’s software
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cross-talk were assessed 25
Execution of the Squats
The participants performed the high-bar back free,
6PLWKDQGVSOLWVTXDWVXVLQJFURVVWUDLQHUVSRUWV
shoes for consistency among the participants and to
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,QWKHIUHHDQG6PLWKVTXDWVWKH\XVHGWKHVTXDW
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ground, shoulder width stance, unrestricted knee
forward displacement relative to the toes, and push
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VTXDWLVLOOXVWUDWHGLQÀJXUH7KHIUHHDQGVSOLW
VTXDWVZHUHH[HFXWHGXVLQJDQ2O\PSLFNJEDUEHOO

Volume 5, Issue 3, December 2016 | JOURNAL OF FITNESS RESEARCH 72
DQGD/LIH)LWQHVV+DPPHU6WUHQJWKVTXDWUDFN
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Participants were allowed 3-5 mins of rest between
each squat to prevent fatigue affecting the validity of
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conditioning coach using visual observation to
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EMG Signal Processing
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L(0*ZKLFKZHUHFDOFXODWHGRYHUWKHWLPHZLQGRZV
for the concentric and eccentric phases of the squat
separately 25'DWDZHUHDYHUDJHGIRUWULDOVRI HDFK
squat type 259DOXHVRI SHDN(0*506(0*DQG
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ZKHUHWKH6PLWKVTXDWLVFRQVLGHUHGWKHPRVW
controlled type of squat that requires less
stabilisation of the lower limb joints 30
Statistical Analyses
The data were assessed for normality of
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superimposed normal curves, box plots and
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data not meeting the assumptions of normality, the p
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correction factor to account for the infringements of
the normality assumption 317ZRZD\$129$V
were used to accommodate the two independent
variables type-of-squat and phase-of-squatXVLQJ,%0
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RESULTS
7KHPHDQ6'SHDN(0*506(0*DQG
L(0*IRUWKHWKUHHW\SHVRI VTXDWHFFHQWULFDQG
concentric phases, and 5 muscles are presented in
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KLJKHVW(0*DFWLYLW\LQDOOWKUHHW\SHVRI VTXDWLQ
Figure 1: Depiction of the bottom-of-the-squat criterion in the free (left), Smith (middle) and split (right) squats.

Volume 5, Issue 3, December 2016 | JOURNAL OF FITNESS RESEARCH 73
0
100
200
300 Free Squat
ECCEN TRI C
CONCE NTR IC
0
100
200
300
RMS EMG (%)
Smith Squa t
0
100
200
300
VMO VLO BF LG TA
Muscles
Split Squat
0
100
200
300
400 Free Squat
ECCENTRIC
CONCEN TRI C
0
100
200
300
400
iEMG (ȝV)
Smith Squa t
0
100
200
300
400
VMO VLO BF LG TA
Muscles
Split Squat
0
100
200
300 Free Squat
ECCENTRIC
CONCEN TRI C
0
100
200
300
RMS EMG (μV)
Smith Squa t
0
100
200
300
VMO VLO BF LG TA
Muscles
Split Squat
0
200
400
600
Free Squat
ECCENTRIC
CONCEN TRI C
0
200
400
600
Peak EMG ( ȝV)
Smith Squa t
0
200
400
600
VMO VLO BF LG TA
Muscles
Split Squat
Figure 5: Normalised RMS EMG for lower limb muscles in the
free, Smith and split squats. VMO = vastus medialis oblique,
VLO = vastus lateralis oblique, BF = biceps femoris, LG =
lateral gastrocnemius, and TA = tibialis anterior.
Figure 2: Mean ± SD peak EMG for lower limb muscles in the
free, Smith and split squats. VMO = vastus medialis oblique,
VLO = vastus lateralis oblique, BF = biceps femoris, LG =
lateral gastrocnemius, and TA = tibialis anterior.
Figure 3: Mean ± SD RMS EMG for lower limb muscles in the
free, Smith and split squats. VMO = vastus medialis oblique,
VLO = vastus lateralis oblique, BF = biceps femoris, LG =
lateral gastrocnemius, and TA = tibialis anterior.
Figure 4: Mean ± SD iEMG for lower limb muscles in the free,
Smith and split squats. VMO = vastus medialis oblique, VLO
= vastus lateralis oblique, BF = biceps femoris, LG = lateral
gastrocnemius, and TA = tibialis anterior.

Volume 5, Issue 3, December 2016 | JOURNAL OF FITNESS RESEARCH 74
Table 1: Kolmogorov-Smirnov tests of normality. Signicant values for EMG variables, muscles, types of squat, and phases of
the squat. VLO = vastus lateralis oblique, BF = biceps femoris, and TA = tibialis anterior.
Variable Muscle Type of Squat Kolmogorov-Smirnov
6LJQL¿FDQFH
Peak EMG BF Back 0.009
Smith 0.001
Mean EMG BF Smith 0.004
iEMG BF Split 0.001
iEMG TA Smith 0.001
Variable Muscle Type of Squat Kolmogorov-Smirnov
6LJQL¿FDQFH
RMS EMG BF ECC 0.001
CON 0.004
iEMG VLO ECC 0.001
BF ECC 0.005
CON 0.001
Table 2: Results of the two-way ANOVAs for peak EMG. VMO = vastus medialis oblique, VLO = vastus lateralis oblique, BF =
biceps femoris, LG = lateral gastrocnemius, and TA = tibialis anterior.
VMO VLO BF LG TA
Type of Squat p 0.143 0.028 0.003 0.001 0.001
F ratio 2.020 3.819 6.378 26.900 7.621
Ș20.700 0.124 0.191 0.499 0.220
Power 0.399 0.670 0.885 1.000 0.935
Squat Phases p 0.125 0.251 0.001 0.291 0.079
F ratio 2.430 1.344 20.800 1.136 3.206
Ș20.430 0.024 0.279 0.021 0.560
Power 0.750 0.207 0.994 0.182 0.420
Type of
Squat * Phases p 0.844 0.769 0.143 0.831 0.668
F ratio 0.170 0.264 2.016 0.186 0.407
Ș20.006 0.100 0.069 0.007 0.015
Power 0.750 0.900 0.398 0.077 0.112
Statistically significant values in bold (p ≤ 0.01)

Volume 5, Issue 3, December 2016 | JOURNAL OF FITNESS RESEARCH 75
Table 3: Results of the two-way ANOVAs for RMS EMG. VMO = vastus medialis oblique, VLO = vastus lateralis oblique, BF =
biceps femoris, LG = lateral gastrocnemius, and TA = tibialis anterior.
VMO VLO BF LG TA
Type of Squat p 0.772 0.566 0.002 0.001 0.193
F ratio 0.259 0.575 6.923 24.291 1.695
Ș20.010 0.021 0.204 0.474 0.059
Power 0.089 0.141 0.910 1.000 0.341
Squat Phases p 0.268 0.336 0.001 0.186 0.110
F ratio 1.254 0.943 11.402 1.793 2.634
Ș20.023 0.017 0.174 0.032 0.047
Power 0.196 0.159 0.912 0.260 0.357
Type of Squat * Phases p 0.765 0.957 0.658 0.897 0.881
F ratio 0.269 0.044 0.421 0.109 0.127
Ș20.010 0.002 0.015 0.040 0.005
Power 0.900 0.056 0.115 0.066 0.068
Statistically significant values in bold (p ≤ 0.01)
Table 4: Results of the two-way ANOVAs for iEMG. VMO = vastus medialis oblique, VLO = vastus lateralis oblique, BF = biceps
femoris, LG = lateral gastrocnemius, and TA = tibialis anterior.
VMO VLO BF LG TA
Type of Squat p 0.354 0.791 0.001 0.001 0.001
F ratio 1.057 0.236 18.338 0.482 24.871
Ș20.038 0.009 0.404 0.209 0.479
Power 0.226 0.085 1.000 1.000 1.000
Squat Phases p 0.782 0.489 0.061 0.624 0.190
F ratio 0.077 0.485 3.665 0.004 1.760
Ș20.001 0.009 0.064 0.243 0.032
Power 0.059 0.105 0.468 0.077 0.256
Type of
Squat * Phases p 0.820 0.978 0.320 0.970 0.499
F ratio 0.200 0.022 1.165 0.001 0.704
Ș20.007 0.001 0.041 0.600 0.025
Power 0.800 0.053 0.245 0.054 0.163
Statistically significant values in bold (p ≤ 0.01)

Volume 5, Issue 3, December 2016 | JOURNAL OF FITNESS RESEARCH 76
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the three types of squat and both eccentric and
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established across various studies that have reported
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difference in lifted weight between the studies may
explain the discrepancy in muscle activity pre-
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recorded in the concentric phase compared to the
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Table 5: Signicant post-hoc tests. BF = biceps femoris, LG =
lateral gastrocnemius, and TA = tibialis anterior.
Variable & muscle Types of squat p value
Peak BF Smith vs. Split 0.007
Back vs. Split 0.001
Peak LG Smith vs. Split 0.001
Back vs. Split 0.002
Peak TA Smith vs. Split 0.002
RMS BF Smith vs. Split 0.003
Back vs. Split 0.001
RMS LG Smith vs. Split 0.001
Back vs. Split 0.001
iEMG BF Smith vs. Split 0.001
Back vs. Split 0.001
iEMG LG Smith vs. Split 0.001
Back vs. Smith 0.001
iEMG TA Back vs. Split 0.010
Smith vs. Split 0.001

Volume 5, Issue 3, December 2016 | JOURNAL OF FITNESS RESEARCH 77
activity in the free and split squats compared to the
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Therefore, squats may be complemented with other
strength exercises that place focus on hamstring
strength; including stiff deadlifts, nordic curls, and
glute hamstring raises 277KHVHH[HUFLVHVZLOO
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approach of heavy eccentric training reduces power
output but allows for muscular hypertrophy while
gaining strength, therefore eccentric squat training
could be used in pre-season training 14'XULQJWKH
competitive season an eccentric plyometric based
approach would be most suitable as this develops
explosiveness and power 147KHVHSO\RPHWULF
exercises could incorporate split squats, lunges, squat
jumps, box jumps and single leg hopping particularly
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whereas the split squat took about 12 s, indicating
that the two short-duration bilateral squats may be
used for the development of power of the
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takes longer to perform, this exercise is appropriate
as a strength training exercise for both the quadriceps
and hamstrings, whilst developing stabilisation
capability of the lateral subsystem at the knee and
hip 21
The present study is limited to strength trained
males, thus further research may include a wider
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the participants, however foot position may affect
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particular, farther forward placement of the leading
foot recruits the gluteus maximus and hamstrings
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functionality in the squat could incorporate measures
of forces and knee angular kinematics using ground
reaction force platforms combined with automated
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could be performed at differed speeds of the
eccentric and concentric phases, using different loads
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squat modality, in which the quadriceps and gluteus
act as the primary movers to compensate for the lack
of involvement of the hamstrings 177KHPRUH
vertical position of the torso associated with the
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activity of the hamstrings and the spinal erectors 17,
which decreases the maximum weight that the athlete
can lift due to limited capability to utilize the
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more pronounced forward lean of the torso and hip
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hamstrings to be under tension at the bottom of the

Volume 5, Issue 3, December 2016 | JOURNAL OF FITNESS RESEARCH 78
VTXDW7KLVDOORZVWKHKDPVWULQJVWRFRQWULEXWH
prominently to hip extension during the ascent,
utilisation of the posterior chain musculature and
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YDULDQWVXVLQJWKHORZEDUWHFKQLTXH)XUWKHU
kinesiological analysis may be more comprehensive
DQGPHDVXUHWKH(0*DFWLYLW\RI RWKHUPXVFOHV
including the gluteus maximus, adductors and
abductors 3,WLVDSSDUHQWWKDWXQLODWHUDOH[HUFLVHVDUH
important in strength training for improved
performance and injury prevention, especially for
sprinting 87KHUHIRUHXQLODWHUDOYDULDWLRQVRI WKH
VTXDWVKRXOGEHLQYHVWLJDWHGIXUWKHUXVLQJ(0*
CONCLUSION
,QWKLVVWXG\(0*DFWLYLW\RI WKHIUHH6PLWKDQG
VSOLWVTXDWVLQVWUHQJWKWUDLQHGPDOHVZDVDQDO\VHG
0XVFXODUDFWLYLW\ZDVKLJKHULQWKHFRQFHQWULFSKDVH
phase of the three types of squat compared to the
eccentric phase in all muscles examined with the
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%)DQG/*PXVFOHDFWLYLW\FRPSDUHGWRWKHIUHHDQG
6PLWKVTXDWV8OWLPDWHO\WKHIUHHDQG6PLWKVTXDWV
DUHRI JUHDWYDOXHLQWKHGHYHORSPHQWRI 9029/2
DQG7$VWUHQJWK+RZHYHUWKHVSOLWVTXDWVKRXOGEH
incorporated into strength programs to develop the
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VWUHQJWKJDLQVLQWKHSRVWHULRUPXVFOHFKDLQ
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 -RQHV07$PEHJDRQNDU-31LQGO%&6PLWK
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back squat training program on leg power, jump,
and sprint performances in junior soccer
SOD\HUVJournal of Strength & Conditioning Research.
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kinetics and their application to exercise
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Volume 5, Issue 3, December 2016 | JOURNAL OF FITNESS RESEARCH 79
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Journal of Strength & Conditioning Research.
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analysis of mechanical loading characteristics and
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WHFKQLTXHJournal of Strength & Conditioning Research.
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