COUPLING BETWEEN SINGLE MUSCLE-SPINDLE AFFERENT AND EMG IN HUMAN WRIST EXTENSOR MUSCLES - PHYSIOLOGICAL EVIDENCE OF SKELETOFUSIMOTOR(BETA) INNERVATION

Objectives: This study was conducted to find physiological evidence of skeletofusimotor innervation in man. Methods: Discharges of 38 single muscle spindle afferents from m. extensor carpi radialis were recorde d from 9 subjects during steady isometric contractions of wrist extens ion. Correlation between these afferents and rectified surface EMG was investigated by estimating cumulant density function. Results: In the cumulant density estimate between spindle afferent and EMG, a positiv e EMG peak was obtained prior to afferent firing between -30 and -10 m s in 15 afferents (39%). Conclusions: The present finding indicates co upling between spindle afferents and extrafusal activity and suggests the widespread skeletofusimotor innervation in human muscle spindle. ( C) 1998 Elsevier Science Ireland Ltd. All rights reserved.