Long-lasting increases in the tremor of human hand muscles following brief, strong effort.

1. Long-lasting (up to 4 h) increases in finger tremor were produced by intense brief effort to contract the muscle. 2. Similar increases resulted from intense effort which did not contract the muscle because the motor nerve was blocked. 3. Comparable contractions induced electrically failed to give rise to increased tremor. 4. Power spectral analysis (1-15 HZ) revealed that all frequencies of tremor were approximately equally increased. 5. It is concluded that these long-lasting increases in tremor are of central nervous origin.