Kinematics, kinetics and muscle activation patterns of the upper extremity during simulated forward falls

The purpose of this study was to explore the effects of fall type and fall height on the kinematics, kinetics, and muscle activation of the upper extremity during simulated forward falls using a novel fall simulation method. Twenty participants were released in a prone position from a Propelled Upper Limb Fall ARrest Impact System. Impacts occurred to the hands from two fall heights (0.05m and 0.10m) and three fall types (straight-arm, bent-arm, self-selected). Muscle activation from six muscles (biceps brachii, brachioradialis, triceps brachii, anconeus, flexor carpi radialis and extensor carpi radialis) was collected and upper extremity joint kinematics were calculated. Peak Fx (medio-lateral), as well as Fx and Fz (inferior-superior) load rate increased between the 0.05m and 0.10m heights. With respect to fall type, the straight-arm falls resulted in significantly greater Fy (anterior-posterior) impulse and Fy and Fz load rates. The change in elbow flexion angle was greater during the self-selected and bent-arm falls compared to the straight-arm falls; a pattern also seen in the wrist flexion/extension angles. All muscles experienced peak % MVIC prior to the time of the peak force. The results of this study suggest that, to some extent, individuals are capable of selecting an upper extremity posture that allows them to minimize the effects of an impact and it has confirmed the presence of a preparatory muscle activation response.