Functional connectivity of hand-arm muscles during a repetitive dynamic task

The aim of the study was to investigate the temporal changes in functional connectivity between pairs of selected hand-arm muscles. I recorded the surface bipolar electromyographic (EMG) activity of biceps brachii, triceps brachii, deltoideus anterior, serratus anterior, upper and lower trapezius during a repetitive dynamic task performed until participants’ rating of perceived exertion reached eight on Borg’s CR-10. The functional connectivity was assessed in terms of Wiener-Granger-causality (G-causality) between each pair of EMG time series revealing the contribution of one muscle (e.g. Y) to yield an improved prediction of EMG time series of another muscle (e.g. X) at each time point over and above the prediction which could be achieved from previous values of X itself (Y→X). Only the G-causality from deltoid anterior to biceps brachii (deltoid anterior→biceps brachii) increased with time, suggesting a possible co-contraction effect associated with fatigue development. However, the extent of functional connectivity was not associated with time to task termination suggesting the inability of the subjects in this study to adopt a load sharing pattern among the hand and arm muscles assisting them to prolong the time to task termination. Investigating the functional connectivity between the involved muscles in a task can provide some insights to the mechanics of the movement pattern.