Timing of the Vibration of Arm Muscles Affects Grip Force Control

The purpose of the study was to investigate how the timing of application of vibration to the arm muscles affects grip force. Eight healthy subjects performed similar tasks of lifting and holding an object without any vi-bration (NV) and with vibration applied to the extrinsic wrist and finger muscles at different times during the task: 1) applied immediately prior to the task performance (AFV) and 2) during the task performance (DFV). Peak grip force, static grip force, and acceleration of the object were re-corded. Vibration applied to the muscles during the task performance did not affect grip force generation. However, when vibration was applied prior to the task performance, a significant increase in grip force was ob-served. We suggest that the differences in magnitudes of grip force be-tween the conditions are associated with the availability of information from muscle spindles and/or joint and tactile afferents. It appears that vi-bration applied during the task performance affects only muscles spin-dles, while a five-minute vibration applied prior to the lift of the object affects both muscle spindles and joint and tactile afferents. The results of the study provide additional information on the availability of afferent information in the control of grip force.