Data reduction
The variables of UE motor control included reaction time (RT), movement time (MT), peak velocity (PV), percentage of MT when PV occurred (PPV), and movement unit (MU). PV, PPV and MU were calculated in the horizontal plane and vertical direction. RT was defined as the interval between the start signal and onset of reaching, representing preplanning efficiency. MT was defined as the interval between onset and offset of reaching, representing movement efficiency. PV was the maximal endpoint velocity during reaching, which is indicative of the magnitude of force production. The PPV indicated the motor preplanning ability. One MU was defined as one acceleration and one deceleration phase; fewer MUs indicates better movement smoothness.To investigate the trunk motor control during reaching, normalized trunk displacement (nTD), normalized endpoint displacement (nED) and trunk contribution slope (TCS) both before PPV occurred (PPV