Cardiac-locomotor coupling while finger tapping.

Coupling between cardiac and locomotor rhythms has been identified while people walk, run, hop and cycle at cadences natural to them. To test the hypothesis that cardiac-locomotor coupling occurs during finger tapping, we studied 20 normal subjects tapping a telegraph key at a comfortable rate for 10 min. 15 subjects (75%) coupled significantly at one or more single-digit integer ratio (heart/tapping rate), the most common of which was 1:2. Such coupling should be considered a potentially confounding variable when studying finger tapping in subjects with disease or medication affecting heart rate. Also, the identification of coupling during the repetitive activity of small upper-extremity muscles suggests that neither increases in cardiac load nor impact-loading, two suggested explanations for why coupling occurs, are necessary for the phenomenon.