Effects of Load and Posture on the Recruitment of Trunk Muscles

Seven male subjects performed 8 cable lifting and hanging tasks, while trunk kinematics and electromyographic data often trunk muscles were obtained. The objectives of the study were to evaluate trunk muscle recruitment and spine loads resulting from performance of this task in different postures and with different load magnitudes. The eight tasks were combinations of four postures (standing, stooping, kneeling on one knee or both knees) and two levels of load (0 N or 100 N load added to existing cable weight). Results indicated that changes in posture and changes in load magnitude both affected muscle co-activation; however, the influence of these variables were quite different in nature. Increased load magnitude resulted in a generalized increase in the co-activation of all trunk muscles, no matter which posture was employed (p < 0.05). Changes in posture significantly affected trunk muscle recruitment patterns (p < 0.05); however, the posture effect typically involved a relatively small subset of trunk muscles. No significant interactions were detected (p > 0.05), indicating that posture and load effects are both independent and additive.