Sex-related differences in motor control strategies during isometric contractions in the Sorensen test posture with different external loading

BACKGROUND: There is a sex-related difference in strength and endurance in trunk muscles: males have more strength while females have more endurance. OBJECTIVE: Investigate sex-related differences in motor control strategies in back muscles during isometric contractions (IC) in the Sorensen test posture. METHODS: Thirty-six healthy and young volunteers performed different tasks: three maximal voluntary contraction (MVC) tests recorded with a bio-feedback force sensor, and followed by five loaded IC (LIC) tests using bodyweight and loads of 0 to 8 kg with a 2-kg step. Surface electromyography was used to measure the activity of bilateral lumbar paravertebral (LP) and quadratus lumborum (QL) muscles. RESULTS: Sex-related and load-related differences in EMG amplitudes were highlighted during LIC tests. Females showed significantly (p= 0.02) greater EMG amplitude for the highest load (8 kg) than males. Besides, significant differences between low (2 and 4 kg) and high (6 and 8 kg) loads for both LP and QL muscles and for both sexes were observed. Finally, for MVC tests, males produced significantly (p= 1.02e-4) greater strength during MVC tests (4.25 ± 1.37 N/kg vs 2.60 ± 0.78 N/kg). CONCLUSION: The results were clinically relevant to bring attention to load strategy during rehabilitation, particularly in females who seemed to recruit the QL muscle more.