Effect of speed of muscle contraction on physiological tremor in normal subjects and in patients with thyrotoxicosis and myxoedema.

The speed of the ankle jerk and physiological finger tremor in patients with thyrotoxicosis and myxoedema have been compared with those in age-matched control subjects. Tremor amplitude depends on the speed of muscle contraction; the faster muscle contracts the greater is the amplitude of tremor, and vice versa. The frequency of the dominant tremor peak is not affected by the speed of contraction but its size increases as muscle contracts faster. Muscle dynamics is clearly one of many factors influencing physiological tremor but is not responsible for the dominant frequency of tremor at round 9 c/sec.