Paradoxical phenomenon of physiological tremor in prolonged tapping load

Cumulative fatigue caused by a tapping load is investigated by power spectrum analysis of both physiological tremor of the finger and surface electromyogram (EMG) of the forearm muscle controlling the finger. A load for two hours at a rate of 200 taps/minute is performed on ten male subjects. The physiological tremor and the EMG are measured before and during the load. The measurement is performed under the isometric contraction at 10% maximum voluntary contraction in the m. flexor digitorum superficialis. The total power and the slow wave ratio of the power spectrum are evaluated. During the load, both spectra of the physiological tremor and the EMG show the maximum total power at 30 minutes after the load. The total powers of both spectra, however, decrease in the period after 60 minutes. Namely, the results of the physiological tremor and the EMG for prolonged load show the "paradox of fatigue." In order to elucidate the cause of the paradox of fatigue, the slow wave ratio of the EMG spectrum is studied. The ratio increases during the load. The muscle loaded indicates the state close to exhaustion, and the change of the function of the muscle contraction affects the amplitude of the physiological tremor. Therefore, the criterion judging muscular fatigue is denoted due to the change of the amplitude of the physiological tremor.