Comparison of F-waves of motor unit action potentials activated during voluntary contraction

The system for classifying F-waves was developed to study the properties of F-wave and to compare single motor unit (MU) F-waves with motor unit action potentials (MUAPs) activated during voluntary contraction. The F-waves evoked by submaximal stimulation as well as the EMG signals during voluntary contraction at 6 levels of 10-100% of maximum voluntary contraction (MVC) were measured in the tibialis anterior muscles of 3 healthy volunteers. Nine channel F-wave waveforms in a selected electrode array were classified using a template-matching method. After the detection procedure of MUAPs in voluntary EMG signals, the MUAPs were also classified by the same method. Most of the F-waves (88.4%) were composed of a single MUAP. The numbers of MU classified from single MU F-waves in 3 subjects were 12, 12 and 15, and the numbers of MU classified from the voluntary EMG signals at 6 contraction levels were 20, 27 and 24, respectively. A total of 26 single MU F-waves were identified with the MUs extracted from the data during voluntary contractions. The results suggest that the F-waves are composed of a population of the MUs, which are recruited at a wide range of contraction levels. The classification procedures of F-waves and voluntary EMG signals have made it possible to recognize the same MU in both signals and to analysis the firing thresholds of F-waves.