EMG Activity of Four Lower Body Muscles During the Back Squat with Three Different Depths and Loads in Recreationally Trained Females
Authors: Flores Victoria , Becker James , Cotter Joshua A. 
Published: June 2021

IntroductionPrevious studies using electromyography (EMG) have shown that activity of the gluteus maximus (GM), vastus lateralis (VL), biceps femoris (BF), and lateral gastrocnemius (LG) vary with both squat depth and barbell load. However, training recommendations are unclear as to which depth and load results in greater muscle activation. Some studies have shown that squats to below parallel (BP) depth with moderate load activate GM more than above parallel (AP) or parallel (P) depths. Others have shown that GM activity does not change with depth, and that increasing depth and load results in greater VL activity.ObjectiveThe purpose of this study was to compare the muscle activation of the GM, BF, VL and LG during three commonly practiced squat depths and with three relative training loads in recreational female lifters.MethodsFourteen healthy, recreationally active females (mean age: 25.3 ± 6.4 years, height: 1.57 ± 0.08 m, body mass: 63.27 ± 9.04 kg, years of squat experience: 4.0 ± 2.88 years), participated in this study. In the first session, depth‐specific one repetition maximum (1RM) was tested. In the second session, EMG electrodes were placed on the muscle belly of the four muscles on each subject's dominant limb prior to completing a maximum voluntary contraction (MVC) to determine relative intensities for normalizing the EMG signals. Participants then performed squats of AP, P, and BP depth, and with 0, 50, and 85%1RM. Raw EMG signals were full wave rectified and smoothed with a root mean square with a 100‐millisecond window. To determine depth and load effect on each muscle's peak EMG activity, separate 3×3 (depth*load) repeated measures analyses of variance (ANOVA) were used for each muscle with Sidak post hoc comparisons and significance levels set to 0.05.ResultsSignificant depth*load interaction effects for GM and LG were found (p=0.008 and p=0.002, respectively). Post hoc comparisons revealed that at AP depth, GM activity was significantly higher with 85%1RM compared to 50%1RM (p=0.0090) and 0%1RM (p<0.001). At P depth, GM activity was also higher with 85%1RM compared to 50%1RM (p<0.013), and 0%1RM (p<0.0001). Post hoc comparisons revealed LG activity at AP depth was significantly higher with 85%1RM compared to 50%1RM (p=0.003) and 0%1RM (p=0,003). LG activity was also higher at P depth with 85%1RM compared to 0%1RM (p=0.005), and higher at BP with 85%1RM compared to 50%1RM (p=0.026) and 0%1RM (p=0.022). No differences were found for either VL or BF activity, and GM and LG activity when comparing depths at each load.ConclusionsResults show GM activity is largest at AP and P depths with 50 and 85%1RM. This suggests training at higher depths with moderate to heavy loads will promote GM activity. Compared to GM activity, results show LG activity increases with depth, but varies with load. At AP and BP depths, increasing load increases LG activity, but an 85%1RM load is specifically needed at P depth to increase LG activity. This suggests training to all depths preferably with heavy loads, will promote LG activity. Results also show no differences in muscle activation when comparing load at different depths. This proposes that the effect depth has on GM and LG activities are dependent on the load lifted at that depth. Lastly, results show that VL and BF activity remain constant when increasing depth and load. This suggests there is no specific training recommendation to enhance activation of VL and BF, as all three depths and loads will result in the same effect.Support or Funding InformationCSULB ASI – California State University of Long Beach Associated Students Inc.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.