The total force (solid gray line, average across conditions) and synergy index (black line, z-transformed synergy index, ΔVZ) during vibration applied to the hand (VBINT, dash-dot line), to the forearm (VBEXT, solid line), and in the no-vibration condition (VBNO, dashed line) during the discrete quick force production tasks. Averages (with standard error shades) across subjects are presented for ΔVZ.