Muscle fiber conduction velocity at different states of isotonic contraction.

Abstract

Conduction velocity (CV), relative twitch force (RTF) and contraction time (CT) of single muscle fibers (SF) and small muscle fiber bundles (FB) were measured at different states of isotonic contraction with double impulse stimuli at varying interstimulus intervals (ISI) from 0 to 1000 ms in the biceps brachii muscle in vivo. During an isotonic contraction, muscle fibers conducted the action potential on average 0.18 m/s faster along the muscle fiber membrane than did relaxed muscle fibers. This difference was statistically significant (P < 0.001). There was a significant positive correlation between the degree of isotonic contraction and fiber bundle conduction velocity (FBCV) with a first peak at the maximum RTF at an ISI of 9 ms and a second peak at the maximum CT at an ISI of 100 ms.