Figure 5. Single motor unit activity during finger movements with different speeds.

Records show parts of visual tracking movements acquired with the target moving at different overall speeds: 4 deg s⁻¹ in A, 10 deg s⁻¹ in B, and 25 deg s⁻¹ in C. The motor unit and surface EMG were recorded from the common finger extensor. Records show, from above: angle in the metacarpo-phalangeal joint; angular velocity; acceleration, a symbolic representation the motor unit discharge train; instantaneous rate; and surface EMG. An increasing circa 8 Hz modulation of motor unit activity with increasing movement speed may be discerned in the instantaneous rate traces.