Trunk and hip electromyographic activity during single leg squat exercises do sex differences exist?

Purpose/background: Researchers have identified sex-differences in lower extremity muscle activation during functional activities that involve landing and cutting maneuvers. However, less research has been conducted to determine if muscle activation differences occur during rehabilitation exercises. The purpose of this investigation was to determine if sex-differences exist for activation amplitudes of the trunk and hip muscles during four single leg squat (SLS) exercises.

Methods: Eighteen males and 16 females participated. Surface electromyography (EMG) was used to determine muscle activity of the abdominal obliques (AO), lumbar extensors (LE), gluteus maximus (GMX), and gluteus medius (GM) during four SLS exercises. Data were expressed as a percentage of a maximum voluntary isometric contraction (% MVIC). A 2 X 4 mixed-model analysis of variance with repeated measures was used to determine the interaction between sex and exercise on each muscle's activity.

Results: No interaction effect existed between sex and exercise. A main effect for sex existed for the GM and LE. On average, females generated 39% greater GM (27.6 ± 10.4 % MVIC versus 19.8 ± 10.5 % MVIC) and 40% greater LE (8.0 ± 2.8 % MVIC versus 5.7 ± 2.8 % MVIC) activity than males. All subjects, regardless of sex, demonstrated similar GMX and AO activity. Overall EMG values ranged from 11.0 % MVIC to 14.7 % MVIC for the GMX and 5.7 % MVIC to 8.8 % MVIC for the AO.

Conclusions: None of the subjects generated sufficient EMG activity for strength gains. Females generated a moderate level of GM activity appropriate for neuromuscular re-education/endurance. Males generated a low level of GM activity that may not necessarily be sufficient to improve GM function. Subjects exhibited low levels of EMG activity for the other muscles. These findings suggest that clinicians modify and/or prescribe different exercises than those studied herein for the purpose of improving GM, GMX, AO, and LE function.

Level Of Evidence: 3b.