Acceleration time series resulting from repetitive extension-flexion of the hand

Power, or variance, spectra of acceleration records obtained from normal subjects during extension-flexion oscillations of a hand at frequencies between 0.5-5.0 Hz generally contained two or three frequency bands. Partial separation of these oscillations in the time domain was obtained using the method of digital filtering (smoothing). In general, the peak frequency of the lowest frequency band occurred at, or nearly at, the frequency that the subject attempted to maintain during a 16-s digitization period. Consideration of absolute frequencies and the effect of mass on frequency indicated that one of the higher frequency bands was the result of normal hand tremor. For low frequencies of voluntary oscillation (0.5-1.25 Hz), a second, higher frequency band occurred with a peak frequency (3.0-4.25 Hz) within the range (3-6 Hz) usually reported for abnormal hand tremor. For voluntary oscillation frequencies above about 1.5 Hz, this second, higher frequency oscillation generally occurred at twice the frequency of the voluntary oscillation.