Physiological differences in sarcolemmal excitability between human muscles.

ABSTRACT

INTRODUCTION: The sarcolemmal resting membrane potential (RMP) affects muscle excitability, contractility, and force generation. However, there are limited In vivo data on the normal RMP of the human sarcolemma between muscles. We hypothesize that the in vivo RMP may differ between human muscles with different physiological roles. METHODS: Muscle velocity recovery cycles were recorded from a proximal antigravity muscle, the rectus femoris, and compared with paired recordings from a distal non-antigravity muscle, the tibialis anterior, in 34 normal individuals. RESULTS: Significant differences in muscle relative refractory period (3.55 millseconds vs 3.87 milliseconds, P = .002), early supernormality (14.22% vs 10.50%, P < .0001), and late supernormality (5.43% vs 3.50%, P < .0001) were observed. DISCUSSION: The results strongly suggest a less negative RMP in tibialis anterior vs rectus femoris and attest to intermuscle differences in normal excitability and physiology. This novel finding employing an in vivo methodology highlights the need for muscle-specific normative data in future studies.