Context-specific early recruitment of small motor units in the shoulder muscle reflects a reach movement plan

Abstract

We studied the spatial and temporal aspects of response preparation in the anterior deltoid muscle using high-density surface EMG. Our results show that early spatially specific ramping activity that predicted reaction times could be accessed from muscle activity but was absent during isometric force-driven cursor movements. Such ramping activity could be quantified using an accumulator framework across trials, as well as within single trials, but was not observed in isometric reach tasks involving cursor movements.