The Effects of Squat Depth on Electromyography of Eight Lower Extremity Muscles

Abstract

The need to build muscular strength may play a crucial role in a person’s life. This demand may be vital for increased sports performance or to help complete activities of daily living. A common exercise to improve lower extremity strength is the squat exercise. However, optimal squat depth to elicit maximal lower extremity muscle activations has yet to be determined. PURPOSE: To examine the effects of squat depth on electromyography (EMG) of eight lower extremity muscles during three different weighted conditions. METHODS: Eighteen healthy recreationally active individuals (10 males, 8 females, 23 ± 2 years, 70.24 ± 12.72 kg, 1.68 ± 0.06 m) completed the study over two days. The first day was used to collect participants’ one repetition maximum (1RM). On the second day of testing, eight surface EMG electrodes were placed on the rectus femoris, vastus lateralis and medialis, biceps femoris, medial hamstring, and medial gastrocnemius. Once electrodes were placed, subjects warmed up and then were asked to perform five repetitions at body weight (BW), 50% 1RM, and 80% 1RM during a maximal knee flexion (Deep) squat and at 90° knee flexion (Normal) squat. Changes in integrated EMG due to squat depth and load were assessed via a 2×3 repeated measures ANOVA. RESULTS: EMG increased as both weight and condition changed. Significant interaction were observed for the biceps femoris, gluteus maximus, medial gastrocnemius, rectus femoris, vastus lateralis, vastus medialis (p<0.001) and the medial hamstring (p=0.041).The tibialis anterior showed a main effect for weight (p<0.001) and condition (p<0.001). Time was also measured during each condition which showed a significant weight*condition interaction (p=0.001). CONCLUSION: Lower extremity muscle activation is significantly increased during deep squats compared to normal squats, which suggests that individuals could benefit from performing a higher knee flexion squat to increase muscle activation and potentially increase muscle strength. Furthermore, time under tension increased as weight increased and during deep squats. This increase in time under tension would keep fibers activated longer, which could increase strength over time. These results may have training implications for various populations that utilize the squat exercise to achieve health or athletic goals.