The effect of angle and level of exertion on trunk neuromuscular performance during multidirectional isometric activities

Abstract

Study Design. To quantify trunk muscle capability and controllability in different angles and levels of isometric exertion using a torque tracking system.

Objective. To investigate the effect of biaxial isometric exertions on the maximum capability of trunk and to examine the effect of angle and level of isometric exertion on trunk controllability during the tracking task in upright posture.

Summary of Background Data. Combined motions of trunk at varying exertion levels occur in most daily and occupational activities and are important risk factors of low back pain. Few studies have investigated trunk capability and controllability during multidirectional activities with different exertion levels.

Methods. Eighteen asymptomatic young male subjects performed isometric contractions of trunk muscles in 8 angles and 3 levels of exertion. The tracking system included a target, which was a thick line with a round endpoint. Subjects were asked to track the target line (path) and match the endpoint while maintaining torque for 3 seconds by exerting isometric contraction against B200 Isostation. The initial part of the tracking task was named path tracking phase and the final part, endpoint matching phase. Trunk capability was determined by measuring peak torque values obtained during maximal voluntary exertions. Trunk controllability was determined by measuring constant error and variable error during tracking tasks. Analysis of variance with repeated measures design was used to test the effects of angle and level of exertion on trunk capability and controllability.

Results. Trunk capability was significantly decreased during biaxial exertions (P < 0.001). Constant error and variable error were significantly affected by angle (P < 0.001) and level (P < 0.001) of exertion during both phases of the tracking task.

Conclusion. Trunk capability and controllability were significantly decreased during biaxial exertions. Higher exertion levels had a major negative impact on trunk controllability in both uniaxial and biaxial exertions. The results suggested that combined exertions and more strenuous efforts may impair trunk neuromuscular control, increasing the risk of low back pain.