EMG analysis of muscle recr. in squatting

[Curious George]

Here is a small selection of articles which examined muscle activity and
forces during various types of squatting:

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Med Sci Sports Exerc 1997 Apr; 29(4):532-9

EMG analysis of lower extremity muscle recruitment patterns during an
unloaded squat.

Isear JA Jr, Erickson JC, Worrell TW.

During an unloaded squat, hamstring and quadriceps co-contraction has been
documented and explained via a co-contraction hypothesis. This hypothesis
suggests that the hamstrings provide a stabilizing force at the knee by
producing a posteriorly-directed force on the tibia to counteract the
anterior tibial force imparted by the quadriceps. Research support for this
hypothesis, however, is equivocal.

Therefore, the purposes of this study were 1) to determine muscle recruitment
patterns of the gluteus maximus, hamstrings, quadriceps, and gastrocnemius
during an unloaded squat exercise via EMG and 2) to describe the amount of
hamstring-quadriceps co-contraction during an unloaded squat.

Surface electrodes were used to monitor the EMG activity of six muscles of 41
healthy subjects during an unloaded squat. Each subject performed three 4-s
maximal voluntary isometric contractions (MVIC) for each of the six muscles.
Electrogoniometers were applied to the knee and hip to monitor joint angles,
and each subject performed three series of four complete squats in cadence
with a metronome (50 beats.min-1). Each squat consisted of a 1.2-s eccentric,
hold, and concentric phase. A two-way repeated measures ANOVA (6 muscles x 7
arcs) was used to compare normalized EMG (percent MVIC) values during each
arc of motion (0-30 degrees, 30-60 degrees, 60-90 degrees, hold, 90-60
degrees, 60-30 degrees, 30-0 degrees) of the squat. Tukey post-hoc analyses
were used to quantify and interpret the significant two-way interactions.

Results revealed minimal hamstring activity (4-12% MVIC) as compared with
quadriceps activity (VMO: 22-68%, VL: 21-63% of MVIC) during an unloaded
squat in healthy subjects. This low level of hamstring EMG activity was
interpreted to reflect the low demand placed on the hamstring muscles to
counter anterior shear forces acting at the proximal tibia.

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*** The following study showed that if you wish to exercise the glutes, then
a full depth squat is highly recommended.

J Strength Cond Res 2002 Aug; 16(3): 428-32

The effect of back squat depth on the EMG activity of 4 superficial hip and
thigh muscles.

Caterisano A, Moss RF, Pellinger TK, Woodruff K, Lewis VC, Booth W, Khadra T.

The purpose of this study was to measure the relative contributions of 4 hip
and thigh muscles while performing squats at 3 depths. Ten experienced
lifters performed randomized trials of squats at partial, parallel, and full
depths, using 100-125% of body weight as resistance. Electromyographic (EMG)
surface electrodes were placed on the vastus medialis (VMO), the vastus
lateralis, (VL), the biceps femoris (BF), and the gluteus maximus (GM). EMG
data were quantified by integration and expressed as a percentage of the
total electrical activity of the 4 muscles.

Analysis of variance (ANOVA) and Tukey post hoc tests indicated a significant
difference in the relative contribution of the GM during the concentric
phases among the partial- (16.9%), parallel- (28.0%), and full-depth (35.4%)
squats.

There were no significant differences between the relative contributions of
the BF, the VMO, and the VL at different squatting depths during this phase.
The results suggest that the GM, rather than the BF, the VMO, or the VL,
becomes more active in concentric contraction as squat depth increases.

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*** This study concluded that that stance width does not cause significant
isolation within the quadriceps but does influence muscle activity on the
medial thigh and buttocks.

Med Sci Sports Exerc 1999 Mar;31(3):428-36

Stance width and bar load effects on leg muscle activity during the parallel
squat.

McCaw ST, Melrose DR.

PURPOSE: Altering foot stance is often prescribed as a method of isolating
muscles during the parallel squat. The purpose of this study was to compare
activity in six muscles crossing the hip and/or knee joints when the parallel
squat is performed with different stances and bar loads.

METHODS: Nine male lifters served as subjects. Within 7 d of determining IRM
on the squat with shoulder width stance, surface EMG data were collected (800
Hz) from the rectus femoris, vastus medialis, vastus lateralis, adductor
longus, gluteus maximus, and biceps femoris while subjects completed five
nonconsecutive reps of the squat using shoulder width, narrow (75% shoulder
width), and wide (140% shoulder width) stances with low and high loads (60%
and 75% 1RM, respectively). Rep time was controlled. A goniometer on the
right knee was used to identify descent and ascent phases. Integrated EMG
values were calculated for each muscle during phases of each rep, and the
5-rep means for each subject were used in a repeated measures ANOVA (phase x
load x stance, alpha = 0.05).

RESULTS: For rectus femoris, vastus medialis, and vastus lateralis, only the
load effect was significant. Adductor longus exhibited a stance by phase
interaction and a load effect. Gluteus maximus exhibited a load by stance
interaction and a phase effect. Biceps femoris activity was highest during
the ascent phase.

CONCLUSION: The results suggest that stance width does not cause isolation
within the quadriceps but does influence muscle activity on the medial thigh
and buttocks.

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*** This study confirmed that there are significant differences in muscle
recruitment patterns between the trunk extensor and hip extensor strategies
of squatting throughout the range of movement. Unfortunately many personal
trainers and fitness "authorities" are sufficiently aware of these
differences.

Spine 1994 Mar 15;19(6):687-95

Electromyographic activity of selected trunk and hip muscles during a squat
lift. Effect of varying the lumbar posture.

Vakos JP, Nitz AJ, Threlkeld AJ, Shapiro R, Horn T.

Electromyographic (EMG) activity of selected hip and trunk muscles was
recorded during a squat lift, and the effects of two different lumbar spine
postures were examined. Seven muscles were analyzed: rectus abdominis (RA),
abdominal obliques (AO), erector spinae (ES), latissimus dorsi (LD), gluteus
maximus (GM), biceps femoris (BF), and semitendinosus (ST). The muscles were
chosen for their attachments to the thoracolumbar fascia and their potential
to act on the trunk, pelvis, and hips. Seventeen healthy male subjects
participated in the study. Each subject did three squat lifts with a 157-N
crate, with the spine in both a lordotic and kyphotic posture. The lift was
divided into four equal periods. EMG activity of each muscle was quantified
for each period and normalized to the peak amplitude of a maximal voluntary
isometric contraction (MVIC). A two-way analysis of variance (ANOVA) for
repeated measures was used to analyze the effects of posture on the amplitude
and timing of EMG activity during the lift.

Two patterns of EMG activity were seen: a trunk muscle pattern (RA, AO, ES,
and LD) and a hip extensor pattern (GM, BF, ST).

1. In the trunk muscle pattern (TP), EMG activity was greatest (in RA, AO,
ES, and LD) in the first quarter and decreased as the lift progressed.

2. In the hip extensor pattern (HP), EMG activity was least (in GM, BF, ST)
in the first quarter, increased in the second and third quarters, and
decreased in the final phase of the lift.

Differences were seen among subjects and in the timing of the muscle activity
in all muscles.

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*** This study showed that there are major differences in muscle recruitment
and joint torque between Weightlifting and Powerlifting squats. In
particular, Weightlifters distribute the load more equally between hip and
knee, whereas Powerlifters put relatively more load on the hip joint. The
thigh muscular activity was found to be slightly higher for powerlifters.
Note that Sumo style squats were not examined in this study, but it would
probably have been found that this places even greater load on the hips as
compared with the knees.

Med Sci Sports Exerc 1996 Feb;28(2):218-24

High- and low-bar squatting techniques during weight-training.

Wretenberg P, Feng Y, Arborelius UP.

Eight Swedish national class weightlifters performed "high-bar" squats and
six national class powerlifters performed "low-bar" squats, with a barbell
weight of 65% of their 1 RM, and to parallel- and a deep-squatting depth.
Ground reaction forces were measured with a Kistler piezo-electric force
platform and motion was analyzed from a video record of the squats. A
computer program based on free-body mechanics was designed to calculate
moments of force about the hip and knee joints. EMG from vastus lateralis,
rectus femoris, and biceps femoris was recorded and normalized. The peak
moments of force were flexing both for the hip and the knee.

The mean peak moments of force at the hip were for the weightlifters 230 Nm
(deep) and 216 Nm (parallel), and for the powerlifters 324 Nm (deep), and 309
Nm (parallel). At the knee the mean peak moments for the weightlifters were
191 Nm (deep) and 131 Nm (parallel), and for the powerlifters 139 Nm (deep)
and 92 Nm (parallel). The weightlifters had the load more equally distributed
between hip and knee, whereas the powerlifters put relatively more load on
the hip joint. The thigh muscular activity was slightly higher for the
powerlifters.

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***The following study concluded that the use of a weight belt during squats
may affect the path of the barbell and speed of the lift without altering
electric activity of the muscles. This suggests that the use of a weight belt
may increase explosive power by increasing the speed of the movement without
compromising the joint range of motion or overall lifting technique. So much
for all the claims about belts being of no value in lifting.

J Strength Cond Res 2001 May;15(2):235-40

The effects of a weight belt on trunk and leg muscle activity and joint
kinematics during the squat exercise.

Zink AJ, Whiting WC, Vincent WJ, McLaine AJ.

Fourteen healthy men participated in a study designed to examine the effects
of weight-belt use on trunk- and leg-muscle myoelectric activity (EMG) and
joint kinematics during the squat exercise.

Each subject performed the parallel back squat exercise at a self-selected
speed according to his own technique with 90% of his IRM both without a
weight belt (NWB) and with a weight belt (WB). Myoelectric activity of the
right vastus lateralis, biceps femoris, adductor magnus, gluteus maximus,
and erector spinae was recorded using surface electrodes. Subjects were
videotaped from a sagittal plane view while standing on a force plate. WB
trials were completed significantly faster than NWB trials over the entire
movement and in both the downward phase (DP) and upward phase (UP).

No significant differences in EMG were detected between conditions for any
of the muscle groups or for any joint angular kinematic variables during
either phase of the lift. The total distance traveled by the barbell both
anteriorly and vertically was significantly greater (p 0.01) in the WB
condition than the NWB condition. The velocity of the barbell was
significantly greater both vertically and horizontally during both the DP
and UP in the WB condition as compared with the NWB condition.

These data suggest that the use of a weight belt during the squat exercise
may affect the path of the barbell and speed of the lift without altering
myoelectric activity. This suggests that the use of a weight belt may improve
a lifter's explosive power by increasing the speed of the movement without
compromising the joint range of motion or overall lifting technique.

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Dr Mel C Siff
Denver, USA

Take Good Care,

Cg