Fig. 4

Transitory force decrease at sudden and sinusoidal changes in the stimulation frequency. a, sample recording of the tetanic contraction for a single fast resistant motor unit stimulated with sudden switches (at 2 Hz) in stimulation frequency (75 and 30 Hz). b, sample recording of the tetanic contraction for a fast resistant motor untit stimulated with sinusoidal changes (2 Hz) in stimulation frequency ranging from 9 to 16 Hz. The horizontal lines indicate the expected force at lower stimulation frequencies