Fig. 2

Experimental protocol for GRASP sub-experiment (a) and GESTURE sub-experiment (b). (a) Each day, the subject would perform 7 grasps. The sequence of 7 grasps was the same during the experiment period. In each session, the subject would perform 3 tasks of different force level. Each task contained 2 same trials lasting for 30 s: 5 s rest, 5 s isometric ramp up from rest to an intensity level, 10 s hold contraction, 5 s isometric ramp down to rest, and 5 s rest. (b) Each day, the participant would perform 5 same trials, each of them lasting for 180 s. In each trial, the participant would perform 11 gesture tasks. Each gesture task lasted for 10 s, with a 5 s rest between two neighboring tasks. There was also a 5 s rest at the beginning of the trial and 20 s rest at the end. A 180 s rest was set between trials to let the subject relax.