Coupling between single muscle spindle afferent and EMG in human wrist extensor muscles: physiological evidence of skeletofusimotor (beta) innervation.
OBJECTIVE
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 recorded from 9 subjects during steady isometric contractions of wrist extension. 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 positive EMG peak was obtained prior to afferent firing between -30 and -10 ms in 15 afferents (39%).


CONCLUSIONS
The present finding indicates coupling between spindle afferents and extrafusal activity and suggests the widespread skeletofusimotor innervation in human muscle spindle.
Kakuda
N
N
Department of Neurology, National Rehabilitation Center for the Disabled, Tokorozawa, Saitama, Japan. J90016@simail.ne.jp
Miwa
T
T
Nagaoka
M
M
D000328:Adult; D004576:Electromyography; D005260:Female; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D008297:Male; D008875:Middle Aged; D009046:Motor Neurons / Q000502:physiology; D009470:Muscle Spindles / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation* / Q000502:physiology; D009475:Neurons, Afferent / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology; D019415:Torque; D014836:Volition / Q000502:physiology; D014955:Wrist Joint / Q000502:physiology*