Evidence for the use of dynamic maximum normalization method of muscle activation during weighted back squats

Abstract

Electromyography (EMG) is a popular technique for analyzing muscle activation profiles during athletic maneuvers such as the back squat. Two methods are commonly implemented for normalizing EMG: a maximum voluntary isometric contraction (MVIC) and a dynamic maximum during the task being performed (DMVC). Although recent literature suggests DMVC may be superior, these suggestions havent been examined for weighted exercises. This study examined the influence of normalization method on rectus femoris, vastus medialis, and biceps femoris activations during back squats. Muscle activations were collected on twenty-seven participants (13 females, 14 males) performing one-repetition maximum (DMVC) and submaximum (80%) back squats. Data from submaximum squats were normalized to MVICs and DMVC. Data were compared using intra-class correlations over two testing days, variance ratio, and coefficients of variation. Mixed-model ANOVAs were used to elucidate the influence on intra-participant (method) and inter-participant (sex) variability. Reliability was "good" or "excellent" for MVIC and "excellent" for DMVC. Inter-subject variability was greater for MVIC compared to DMVC for all muscles. A significant normalization by sex interaction for both peak and mean biceps femoris activation was found. Based on our findings and current literature, normalization to DMVC is the superior method for weighted exercises.

Keywords: Back squat; Electromyography; Muscle activation; Sex differences.