Effect of trunk posture on external and internal oblique muscles' activities during forced expiration

Abstract

Introduction: The activities of external oblique (EO) and internal oblique (IO) muscles during forced expiration in a trunk-neutral posture are insufficient for muscle strengthening. Furthermore, these activities during forced expiration may be affected by trunk postures, which can change respiratory muscle activity. Therefore, this study aimed to evaluate the effects of trunk posture on the EO and IO muscles' activities during forced expiration.

Methods: Thirty healthy males participated in this study. The participants were placed in the supine position with their trunks in the neutral, right rotation, or right lateral trunk flexion position, and their bilateral EO and IO muscles' activities during forced expiration were measured using surface electromyography.

Results: The right EO muscle's activity during forced expiration was significantly higher in the right trunk flexion position than in the neutral trunk and right trunk rotation positions (p < 0.05 and p < 0.001, respectively) but was significantly lower in the right trunk rotation than in the neutral trunk (p < 0.01). In contrast, the left EO muscle's activity was significantly higher in the right trunk rotation position than in the neutral trunk and right lateral trunk flexion positions (p < 0.001 for both) but was significantly lower in the right lateral trunk flexion position than in the neutral trunk position (p < 0.01). The bilateral IO muscles' activity during forced expiration did not significantly differ among the three postures.

Conclusion: The findings indicated that the bilateral EO muscles' activity during forced expiration was affected by trunk posture.

Keywords: External oblique; Forced expiration; Internal oblique; Trunk posture.