The relationship between wrist-monitored motor activity and serum CPK activity in psychiatric in-patients.

Motor activity, monitored by a wrist motion transducer, was related to serum CPK activity the following morning in a group of psychiatric in-patients. In 4 of 10 patients, studied for periods exceeding one week, total 24-hour activity was significantly correlated with morning serum CPK activity. Motor activity during the night was unrelated to serum CPK activity. In a larger group of 30 patients, studied for one or two-day periods, inter-individual differences in activity level were not related to serum CPK activity, although both sex and race were significantly related to variance between subjects in that activity.