Characteristics of physiologic tremor in young and elderly adults

Objective: To determine the prevalence of tremor-related motor-unit entrainment in young and elderly adults. Methods: Postural hand tremor in neurologically healthy people, age ranges 20–42 (59 women and 41 men) and 70–92 (50 women and 50 men) years, was studied with accelerometry and forearm electromyogram (EMG). Tremor was recorded with and without a 300 g load distributed over the distal half of the horizontally extended hand and was analyzed with Fourier spectral techniques. Results: No tremor-related spectral peak was found in the EMG of 59 young and 65 elderly controls, and inconsistent EMG peaks were observed in 29 young and 21 elderly. Twelve young and 14 elderly people exhibited a well-defined tremor-coherent EMG peak with and without 300 g loading, and the frequency of the EMG peak decreased less than 1 Hz in 8 young and 7 elderly. The EMG peak frequency was 9–12 Hz during mass loading in all 8 young adults but in only two elderly adults. The other 5 elderly people had peak frequencies at 5–7 Hz. Age had no significant effect on the frequency and amplitude of the mechanical-resonant component of hand tremor. Conclusions: Approximately 8% of young and elderly adult controls have an EMG-acceleration pattern that is indistinguishable from mild essential tremor. Significance: These results provide a framework for the interpretation of electrophysiologic studies in patients with suspected essential tremor.