Muscle Action in the Squat

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This research article analyses muscle involvement in the powerlifting squat.

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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Dr Mel C Siff

Denver, USA

http://groups.yahoo.com/group/Supertraining/