Activation level of extensor carpi ulnaris affects wrist and elbow acceleration responses following simulated forward...

The main objective of this study was to measure the acceleration response at the wrist and elbow as a function of different levels of isometric forearm muscle activation during the impact phase of a simulated forward fall. A seated human pendulum was designed to impact the hands of 28 participants while maintaining one of four levels of isometric muscle activation (12%, 24%, 36% and 48% maximal voluntary exertion (MVE)) in the extensor carpi ulnaris muscles. The acceleration responses including peak acceleration (PA), acceleration slope (AS) and time to peak acceleration (TPA) were measured at the wrist and elbow along two axes (axial and off-axis) with two low mass surface mounted accelerometers. At the wrist, significant muscle activation effects were found for PA(off), AS(axial), AS(off), such that they increased as muscle activation increased from baseline to 48% MVE. At the elbow, a similar response was noted, with the acceleration variables increasing as muscle activation level increased, except for AS(off). The results suggest that increases in muscle activation from 12% to 48% MVE stiffen the forearm complex and increase the transmissibility of the impact reaction force shock waves through the forearm.