428 Journal of Strength and Conditioning Research, 2002, 16(3), 428–432  2002 National Strength & Conditioning Association The Effect of Back Squat Depth on the EMG Activity of 4 Superficial Hip and Thigh Muscles ANTHONY CATERISANO, RAYMOND F. MOSS, THOMAS K. PELLINGER, KATHERINE WOODRUFF, VICTOR C. LEWIS, WALTER BOOTH, AND TARICK KHADRA The Department of Health and Exercise Science, Furman University, 3300 Poinsett Highway, Greenville, South Carolina 29613. ABSTRACT The purpose of this study was to measure the relative con- tributions of 4 hip and thigh muscles while performing squats at 3 depths. Ten experienced lifters performed ran- domized trials of squats at partial, parallel, and full depths, using 100–125% of body weight as resistance. Electromyo- graphic (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 quan- tified 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 (p  0.001*, p = 0.056**) in the relative contribu- tion of the GM during the concentric phases among the par- tial- (16.9%*), parallel- (28.0%**), and full-depth (35.4%*) squats. There were no significant differences between the rel- ative contributions of the BF, the VMO, and the VL at differ- ent 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 increas- es. Key Words: resistance training, biceps femoris, vastus medialis, vastus lateralis, gluteus maximus Reference Data: Caterisano, A., R.F. Moss, T.K. Pellin- ger, K. Woodruff, V.C. Lewis, W. Booth, and T.Khadra. The effect of back squat depth on the EMG activity of 4 superficial hip and thigh muscles. J. Strength Cond. Res. 16(3):428–432. 2002. Introduction R ecently, in the resistance training literature there appears to be a growing interest in the effect of exercise variation on muscle activity patterns during standard lifts. These studies have traditionally used electromyography (EMG) as the primary method of identifying muscle group contribution while compar- ing different body positions during a lift. Studies on grip width variation in the bench press (1), as well as several studies on variations in the weighted back squat (3, 8, 9), have focused on testing both published and anecdotal information on the effects of changing specific variables in the lifting technique. The weighted back squat appears to be one of the more popular resistance exercises tested for muscle group involvement with variation in the lifting tech- nique. McCaw and Melrose (3) found that variation in stance width during the squat did not affect isolation of muscles in the quadriceps, which is contrary to what many weight lifters believe. In an earlier study Signorile et al. (8) suggested that foot position varia- tion during the parallel squat did not affect quadriceps muscle use patterns. Wretenberg et al. (9) evaluated 2 squatting depths and bar placement as variables in muscle group involvement in 2 groups of trained sub- jects. Their conclusions suggested greater thigh muscle activity among the subjects performing the ‘‘low-bar’’ squat than in the group using the ‘‘high-bar’’ tech- nique. They also reported differences in peak muscular activity in the rectus femoris when comparing a par- allel squat with a deep squat. However, they attribute this to differences in ‘‘forward lean’’ among the power lifters in the study, who were bigger in size and lifted heavier weights than did the Olympic style lifters, who lifted much lighter loads. During the squatting depth portion of the study, Wretenberg also reported no sig- nificant difference in muscle activity in the other thigh muscles, including the vastus lateralis (VL), and the long head of the biceps femoris (BF). This last point is interesting because a popular weight training text by Pauletto suggested that a deeper squat will activate the hamstrings more than a partial squat can (6). In reviewing previous research on variation in the weighted back squat, it appears that monitoring the activity of the gluteus maximus (GM) might help ex- plain the differences in thigh muscle activity at differ- ent squatting depths. Many experts feel that the GM is a key prime-mover muscle in the squat and should