caterisano, anthony 2002 - the effect of back squat depth on the emg activity of 4 superficial hip...

428

Journal of Strength and Conditioning Research, 2002, 16(3), 428–432q 2002 National Strength & Conditioning Association

The Effect of Back Squat Depth on the EMGActivity 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 performingsquats 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 vastusmedialis (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 thetotal electrical activity of the 4 muscles. Analysis of variance(ANOVA) and Tukey post hoc tests indicated a significantdifference (p , 0.001*, p 5 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 suggestthat the GM, rather than the BF, the VMO, or the VL, becomesmore active in concentric contraction as squat depth increas-es.

Key Words: resistance training, biceps femoris, vastusmedialis, 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 of4 superficial hip and thigh muscles. J. Strength Cond.Res. 16(3):428–432. 2002.

Introduction

Recently, in the resistance training literature thereappears to be a growing interest in the effect of

exercise variation on muscle activity patterns duringstandard lifts. These studies have traditionally usedelectromyography (EMG) as the primary method ofidentifying muscle group contribution while compar-ing different body positions during a lift. Studies ongrip width variation in the bench press (1), as well as

several studies on variations in the weighted backsquat (3, 8, 9), have focused on testing both publishedand anecdotal information on the effects of changingspecific variables in the lifting technique.

The weighted back squat appears to be one of themore popular resistance exercises tested for musclegroup involvement with variation in the lifting tech-nique. McCaw and Melrose (3) found that variation instance width during the squat did not affect isolationof muscles in the quadriceps, which is contrary towhat many weight lifters believe. In an earlier studySignorile et al. (8) suggested that foot position varia-tion during the parallel squat did not affect quadricepsmuscle use patterns. Wretenberg et al. (9) evaluated 2squatting depths and bar placement as variables inmuscle group involvement in 2 groups of trained sub-jects. Their conclusions suggested greater thigh muscleactivity among the subjects performing the ‘‘low-bar’’squat than in the group using the ‘‘high-bar’’ tech-nique. They also reported differences in peak muscularactivity in the rectus femoris when comparing a par-allel squat with a deep squat. However, they attributethis to differences in ‘‘forward lean’’ among the powerlifters in the study, who were bigger in size and liftedheavier weights than did the Olympic style lifters, wholifted much lighter loads. During the squatting depthportion of the study, Wretenberg also reported no sig-nificant difference in muscle activity in the other thighmuscles, including the vastus lateralis (VL), and thelong head of the biceps femoris (BF). This last point isinteresting because a popular weight training text byPauletto suggested that a deeper squat will activate thehamstrings more than a partial squat can (6).

In reviewing previous research on variation in theweighted back squat, it appears that monitoring theactivity 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 GMis a key prime-mover muscle in the squat and should

Squat Depth and EMG Activity 429

be included in a surface electrode EMG analysis of thelift (4, 5). The purpose of this study was to test theeffect of 3 different squatting depths on the relativecontributions of 4 hip and thigh muscles during theweighted back squat.

MethodsExperimental Approach to the ProblemPilot data collected during the initial phase of thisstudy revealed some of the same methodological con-cerns stated in the Introduction. In our attempt to nor-malize the data with a 1 repetition maximum (1RM)squat, the forward lean problems observed in the pilottrials among our subjects were found to be similar tothose reported previously (9). The fatiguing effect as-sociated with heavy resistance (e.g., 1RM) was also aconcern because our research design was devised us-ing the same subject for all squatting depths. We alsodecided to test each subject in 1 session to avoid thepotential error associated with the exact replacementof electrodes in multiple data collection sessions. Toprevent these potential sources of data variability, ourapproach was to avoid normalizing the data to a 1RMand instead to compare the electrical activity of eachmuscle with the total electrical activity of all the 4muscles tested using submaximal workloads. In otherwords, because we were most concerned with the rel-ative contribution of each muscle compared with thatof the other 3, this approach appeared to be a justifi-able alternative when compared with the potentialproblems associated with normalizing the data usinga 1RM.

Selecting the muscles to be monitored was anotherconcern in the present study. Recognizing that the GMhas not been monitored in previous studies, this mus-cle was chosen in light of past research, which sug-gests that it is an important muscle in weighted backsquats (4, 5). Our pilot data indicated that the clearestEMG signal was attained in subjects who possessed arelatively low percentage of body fat (e.g., #10%). Theother 3 muscles (VL, vastus medialis [VMO], and BF)were selected because these muscles were often tar-geted for development via back squats, according tomost sources (4–7).

SubjectsTen experienced male weight lifters volunteered assubjects for this study. Descriptive characteristics ofthe subjects were as follows: age 5 24.3 6 5.6 years,body mass 5 86.1 6 11.2 kg, height 5 182.6 6 6.9 cm,and estimated percent body fat 5 6.1 6 1.8 % (mean6 SD). All subjects had an extensive training historywith free weights ($5 years experience), and all hadexperience in performing at all the squatting depthstested, including full squats (ø0.79 rad at the kneejoint), in their workouts. The subjects read and signedinformed consent forms, and the Furman University

Human Subjects Review Board approved all the pro-cedures.

Experimental Procedures

Two days before testing, each subject underwent a fa-miliarization session in which all 3 squatting depthswere practiced with a weight equivalent to between100 and 125% of each subject’s body weight. Each sub-ject chose a weight that was commensurate with hisability to perform the 3 squatting depths with a properand consistent technique, within the limitations ofstandard barbell weight configurations. On the day oftesting, each subject performed a standardized warm-up (nonresistant movements, light-weighted squatsand stretching) and was prepared for randomized tri-als, with all trials being performed in 1 session. Foursuperficial muscles of the right hip and thigh werecleaned and abraded to reduce interelectrode resis-tance. Three EMG surface electrodes (disposable sil-ver–silver chloride electrodes placed in a bipolar con-figuration 2.5 cm apart, plus a reference electrode)were placed on the bellies of each muscle. The musclestested were the VL, the VMO, the BF, and the GM.Subject preparation also included the affixing of re-flective joint markers on all the visible joints of theright side of the body (hip joint, knee joint, ankle joint,lateral aspect of the calcaneus, and lateral fifth meta-tarsal), as well as on the center of the bar, for a side-view filming of each trial (Panasonic AG-188U filmingat 60 fields per second interfaced with a Gateway E-4200 using the Peak Motus Measurement system, PeakPerformance Technologies, Englewood, CO; video tap-ing speed of 60 Hz). This 2-dimensional spatial modelof video analysis was set up to insure proper depthon each squat. In addition, all trials were performedwith the subject standing on a force platform (AMTILG6-4-200, Advanced Mechanical Technology, Inc.,Watertown, MA), with feet a shoulder width apartwith 3 forces and 3 moments measured (Fx, Fy, Fz,Mx, My, Mz). The force plate data were sampled at2,000 samples per second (4,000 gain; Butterworth fil-ter). To insure the precise location of the exact startand end of each phase of the lift (downward move-ment involving eccentric muscle contractions, upwardmovement involving concentric muscle contractions),the digitized video data were synchronized with theEMG and force plate data by computer.

The EMG activity of each muscle was measuredusing the Biopac system EMG (BIOPAC Systems, Inc.,Santa Barbara, CA), with a high-pass frequency filter,and the bipolar electrode system. Trials were random-ized to control for order effect, and each subject per-formed 3 repetitions of weighted back squats with thebar placed across the top of the posterior deltoids. Af-ter a warm-up routine the experimental trials wereperformed with a fixed weight equivalent to 100–125%of each subject’s body weight. Each subject was al-

430 Caterisano, Moss, Pellinger, Woodruff, Lewis, Booth, and Khadra

Table 1. Percent contribution (mean 6 SD) of each thigh muscle during the upward (concentric) phase of the squat formean integrated electromyographic analysis data.

Thigh muscle Partial squat (%) Parallel squat (%) Full squat (%)

Biceps femorisGluteus maximusVastus medialisVastus lateralis

13.37 6 6.9716.92 6 8.78*30.88 6 16.18***38.82 6 17.37

15.35 6 10.1228.00 6 10.29**18.85 6 8.7637.79 6 13.37

15.01 6 7.9135.47 6 1.45*20.23 6 8.1029.28 6 10.72

* p , 0.01.** p 5 0.056.*** p 5 0.07.

Table 2. Percent contribution (mean 6 SD) of each thigh muscle during the downward (eccentric) phase of the squat formean integrated electromyographic analysis data.



8.77 6 3.5113.05 6 7.6639.84 6 10.2638.34 6 7.12

6.85 6 3.1010.91 6 4.2243.25 6 10.6139.00 6 12.42

9.32 6 8.1913.03 6 6.6743.21 6 12.5034.61 6 10.30

lowed at least 3 minutes of rest between trials to min-imize fatigue as a contaminating variable. The inde-pendent variable within each trial was as follows: (a)partial squats in which the angle between the femurand the tibia was approximately 2.36 rad at the kneejoint, (b) parallel squats in which the angle betweenthe femur and the tibia was approximately 1.57 rad atthe knee joint, and (c) full squats in which the anglebetween the femur and the tibia was approximately0.79 rad at the knee joint. Each subject was also in-structed to maintain a consistent upper-body positionfor each trial. An investigator provided verbal cues foreach subject when they were at the proper squattingdepth, and proper depth was verified by cinematog-raphy analysis from the data collected during filming.If it was determined that proper depth was notachieved or that upper-body lean was excessive (.0.17rad), that trial was replaced into the random draw tobe repeated. This affected only 1 subject in 1 trial inthe present study.

Statistical AnalysesEMG data were collected during both the concentricand the eccentric phases of each squat, quantified byintegration, and expressed as both peak and meanelectrical activity for each phase of the lift. Data fromeach muscle were normalized by being expressed as apercent contribution to the total electrical activity ofall the 4 muscles tested. Although other similar studieshave normalized data relative to some maximal effort,our approach was designed to avoid the upper-bodydeviations, reported in previous work (9), that oc-curred as the subjects changed their upper-body po-

sition at different squatting depths with maximal re-sistance. The data from the 3 repetitions at each squat-ting depth were averaged to minimize the potentialvariation from repetition to repetition. A repeated-measures ANOVA (4 3 3 factorial; muscle group bysquatting depth) with a Tukey post hoc test was usedto determine the statistical significance of differencesin the electrical activity of each muscle tested duringeach trial.

Results

The results of the integrated electomyographic analy-sis (IEMG), calculated as the percent contribution ofeach muscle to the total electrical activity of the 4 thighmuscles monitored, are presented in Tables 1–4. Table1 includes data on the upward (concentric) phase ofthe squat, in which the average IEMG of each musclegroup was reported. Table 2 represents the downward(eccentric) phase of the lift with the average IEMGdata. Tables 3 and 4 represent the peak IEMG valuesfor the concentric and eccentric phases of the lift, re-spectively.

Discussion

The results of this study suggest that the GM is themuscle group that displays the most varied contribu-tion during the concentric phase of the weighted backsquat among the 3 squatting depths tested. The other3 muscles monitored (BF, VMO, and VL) appear toshow more consistency during the concentric phase ofweighted squats at these squatting depths, relative to

Squat Depth and EMG Activity 431

Table 3. Percent contribution (mean 6 SD) of each thigh muscle during the upward (concentric) phase of the squat forpeak integrated electromyographic analysis data.



26.02 6 9.6726.81 6 8.0226.70 6 7.3420.46 6 8.37

26.92 6 10.9027.41 6 13.8328.85 6 9.9717.45 6 12.43

19.35 6 6.5040.50 6 13.83*19.29 6 6.20*20.86 6 9.37

* p , 0.05.

Table 4. Percent contribution (mean 6 SD) of each thigh muscle during the downward (eccentric) phase of the squat forpeak integrated electromyographic analysis data.



23.41 6 11.1627.74 6 16.3626.90 6 7.9821.94 6 12.46

23.94 6 12.9832.80 6 17.7723.56 6 7.4119.68 6 12.88

27.94 6 10.8525.57 6 13.4025.15 6 14.1021.34 6 9.65

their respective contribution to the lift. The 1 exceptionto this is the average IEMG activity of the VMO whencomparing the partial squat with the other 2 depths.The VMO contributes 30.88% to the total electrical ac-tivity of the thigh during the partial squat; yet, it con-tributes only 18.85 and 20.23% during the parallel andfull squats, respectively. This difference was not statis-tically significant (p 5 0.07). Also, when consideringpeak IEMG activity, the VMO is significantly less ac-tive in the full squat (19.29%, p , 0.05) than in theother 2 squatting depths (parallel at 28.85%, partial at26.70%). This trend among the VMO data suggeststhat VMO becomes more of a contributor, in terms ofelectrical activity, in the partial squat depth but less soduring a full squat. During the eccentric phase of theweighted back squat, the relative contributions of these4 muscle groups at the 3 depths tested were not sta-tistically different for both average and peak IEMGdata.

The results of the present study are consistent withthe other reported results in the literature. Schaub andWorrell (7) evaluated the relative contributions of sev-eral muscle groups that included the VL and the VMOduring a parallel, isometric squat and found no statis-tical difference between those 2 muscles of the quad-riceps. Isear et al. (2) examined muscle group contri-bution during an unloaded squat and suggested thathamstring EMG activity is relatively low when com-pared with the EMG activity of the quadriceps. Wrightet al. (10) also found that hamstring activity duringthe squat is minimal. Although the latter 2 studies didnot include a variety of squatting depths in their de-signs, the low levels of electrical activity reported inthe hamstrings were similar to the results of the pre-sent study.

Wretenberg et al. (9) investigated squatting depthas an independent variable in their research designand examined 2 variations in the lift (parallel vs. fullsquats). Their results were similar to those of the pre-sent study because they reported no significant differ-ence in muscle activity in the VL, the VMO, and theBF between the 2 squatting depths. Their study didnot monitor the electrical activity of the GM in thedesign.

In conclusion, the results of our study support thetheory that increasing the squatting depth (from a par-tial [ø2.36 rad at the knee joint] to a parallel [ø1.57rad at the knee joint] to a full squat [ø0.79 rad at theknee joint]) has no significant effect on the relativecontribution of the BF to the total electrical activity ofthe major muscles involved in the lift. The activity ofthe VL and the VMO also appears to be fairly consis-tent across the 3 depths tested, with the exception ofthose variations reported in the VMO. The primary dif-ference appears to be in the EMG activity of the GMamong these 3 squatting depths.

Practical Applications

Although many popular lay publications and anecdot-al information suggest that the hamstring muscles aremore active during a deep squat, the results of thepresent study suggest otherwise. The BF does not ap-pear to be more active as squatting depth increases. Itappears to be the GM rather than the BF that becomesprogressively more active as squatting depth increasesfrom partial to full. It should also be noted that sub-maximal weights were used in this research design, sothe results may only apply to submaximal weights

432 Caterisano, Moss, Pellinger, Woodruff, Lewis, Booth, and Khadra

used in training. This last point is justifiable becausethe majority of lifters who perform the weighted backsquat typically use submaximal weight in training andin rehabilitation. Perhaps future research could repli-cate this study using maximal weights to examine themuscle activity patterns at higher training loads andto determine if these heavier weights elicit similarmuscle activity as in the present study. Despite thelimitations of the study this information may be usefulamong coaches and trainers for addressing musclegroup specificity in designing resistance training pro-grams. Coaches who wish to target specific hip andthigh muscles may find these results especially useful.It may also have relevance for athletic trainers and oth-ers who engage in rehabilitating injured athletes or as‘‘prehab’’ for preventing lower-body injuries.

References

1. CLEMONS, J.M., AND C. AARON. Effect of grip width on themyoelectric activity of the prime movers in the bench press. J.Strength Cond. Res. 11(2):82–87. 1997.

2. ISEAR, J.A., J.C. ERICKSON, AND T.W. WORRELL. EMG analysisof lower extremity muscle recruitment patterns during an un-loaded squat. Med. Sci. Sports Exerc. 29(4):532–539. 1997.

3. MCCAW, S.T., AND D.R. MELROSE. Stance width and bar load

effects on leg muscle activity during the parallel squat. Med.Sci. Sports Exerc. 31(3):428–436. 1999.

4. MCLAUGHLIN, T.M., C.J. DILLMAN, AND T.J. LARDNER. A kine-matic model of performance in the parallel squat by championpower lifters. Med. Sci. Sports 9:128–133. 1977.

5. O’SHEA, P. The parallel squat. Natl. Strength Cond. J. 7(1):4–7.1985.

6. PAULETTO, B. Strength Training for Coaches. Champaign, IL: Lei-sure Press, 1991.

7. SCHAUB, P.A., AND T.W. WORRELL. EMG activity of six musclesand VMO:VL ratio determination during a maximal squat ex-ercise. J. Sports Rehab. 4:195–202. 1995.

8. SIGNORILE, J.F., K. KWIATKOWSKI, J.F. CARUSO, AND B. ROBERT-SON. Effect of foot position on the electromyographical activityof the superficial quadriceps muscles during the parallel squatand knee extension. J. Strength Cond. Res. 9(3):182–187. 1995.

9. WRETENBERG, P., Y. FENG, AND U.P. ARBORELIUS. High- and low-bar squatting techniques during weight-training. Med. Sci.Sports Exerc. 28(2):218–224. 1996.

10. WRIGHT, G.A., T.H. DELONG, AND G. GEHLSEN. Electromyo-graphic activity of the hamstrings during performance of theleg curl, stiff-leg deadlift, and back squat movements. J. StrengthCond. Res. 13(2):168–174. 1999.

AcknowledgmentsThis study was supported by a grant from The NationalScience Foundation.

Address correspondence to Dr. Anthony Caterisano,[email protected].

caterisano, anthony 2002 - the effect of back squat depth on the emg activity of 4 superficial hip...

Documents