1. 1. The spectrum of physiological tremor has been recorded from the outstretched index finger of eighty-eight healthy subjects with ages between 3 and 85 years, and at frequent intervals over long periods of time in two trained subjects. 2. 2. The shape of the velocity spectrum remained very constant in the individual, although the total root mean square (RMS) error velocity between 1 and 20 c/sec varied from time to time. For the two subjects studied the coefficient of variation averaged about 30%. A well-defined peak at around 9 c/sec was always present in both subjects. Peak frequency rarely shifted by more than 1 c/sec. The relative size of the peak was related to the RMS velocity between 1 and 20 c/sec, peak size increasing as tremor increased. 3. 3. A definite peak was only present in about 60% of the spectra recorded from twenty-seven children with ages less than 16 years, while a peak was obvious in about 95% of the spectra recorded from sixty-one adults. The relative size of the peak was significantly smaller in children than in adults. 4. 4. The relative size of the peak was inversely related to the RMS velocity between 1 and 5 c/sec, peak size increasing as low frequency tremor decreased. The smaller peak size in children, when present, was related to significantly greater low frequency tremor in children compared with adults. It appears that tremor is more commonly organized around a peak frequency in adults than in children. 5. 5. As in the individual, in the group of subjects studied there was a significant relationship between relative peak size and total RMS velocity between 1 and 20 c/sec, peak size increasing as over-all tremor increased. 6. 6. There was no significant difference between peak frequency in children and adults, but peak frequency decreased over about the age of 50 years. Previous reports of a lower peak frequency in children, when calculated visually from analogue tremor records, probably reflect the frequent absence of a peak in childhood. The predominance of low frequency tremor in all spectra would then give the visual impression of a low frequency peak. © 1969.
