Spectral analysis of single-unit discharges, multi-unit EMG and muscle force during voluntary quasi-sinusoidal isometric contractions of two hand muscles revealed corresponding modulations of the firing rates of motor units at the frequency of the force oscillation. These rate modulations were correlated; and they showed a phase advance over the force oscillation, which is consistent with a cause-effect relationship between changes in firing rate and variations in force. These effects, observed over wide ranges of modulation amplitudes and frequencies, confirm the role of rate coding in the generation of time-varying muscle contractions; and they support the idea that during voluntary contraction of a given muscle, the motoneuron pool is subject to a common drive.
Bibliographical noteFunding Information:
Supported by NIH Grant NS 22715 and the McKnight Foundation. This report is based on a Ph.D. dissertation by M.B.I. in the Department of Physiology of the College of Physicians and Surgeons of Columbia University. We are very grateful to Len Zablow for the development of software and for assistance in the analysis of data.
- Frequency analysis
- Human motor unit
- Interosseus muscle
- Sinusoidal isometric force
- Voluntary contraction