Figure 7.

Illustration of the consequences of a restricted motor range on motor signals (A) and muscle activity (B) for the muscles of the shoulder joint during two movements, one of small amplitude (top row) and one of large amplitude (bottom row). The agonist (solid lines) and antagonist (dashed) signals are represented for an average healthy subject (green) or Off-DBS PD patient (blue). The antagonist trace is inverted for clarity. A, As the neuromuscular effort to reach the target is always minimized, the restriction of motor range translates into longer movement times, for movements of small (top) or large amplitude (bottom). The constraint of the motor range also results in a scaling of movement duration (MD) with movement extent (compare MD for a small and a large amplitude, in both an average healthy and PD subject). B, The restricted motor range leads to lower muscle activities. Nevertheless, peak muscle activity scales with movement amplitude (compare the amplitude of the first agonist burst for a small (top) or large (bottom) movement). This can be observed in both healthy and PD subjects, although it is only clearly visible for the former on these graphs.