Effects of two grip force levels and forearm postures on hand-arm transmitted vibration and physiological responses

Vibration transmitted to the upper limb is the primary source of occupational musculoskeletal disorder. Transmissibility is not just caused by vibration magnitude but is also directly influenced by the applied force and posture. This study investigated the effects of two forearm postures and grip force levels, when using dual-handle guided equipment, on hand-arm transmitted vibration and physiological responses. Sixteen young male adults were recruited. Pre-task and post-task assessments including grip strength and perceived discomfort were measured. The task was to hold a vibrating handlebar for 5 -min under four randomly sequenced conditions: N/P_M/H—neutral/pronated forearm and mild/hard grip. Transmissibility and forearm muscle activities were recorded during each task. It was discovered that neutral posture led to higher wrist and elbow transmissibility, whereas hard grip resulted in higher elbow transmissibility, forearm muscle activities, grip strength reduction, and distal arm discomfort. Furthermore, the interaction between the effects of posture and force significantly influenced wrist extensor activity (N_H > P_H; N_M = P_M), proximal arm discomfort (N_H < P_H; N_M = P_M), and wrist transmissibility (P_H > P_M; N_H = N_M). Essentially, with constant vibration and exposure duration, the application of sustained hard grip had more negative physiological effects because of the greater physical workload toward the hands and forearms. Moreover, gripping hard during pronation led to higher discomfort that reached the proximal arm because a greater effort was required. Hence, a neutral forearm posture is recommended when the tasks require forceful movements and either posture is suggested when less powerful movements are involved.