Relation of whole muscle contractile properties to source of innervation.
This work investigated the extent to which constituent proportions of fast- and slow-twitch muscle units determine whole muscle contractile properties. We employed several self- and cross-reinnervation models using synergistic homogeneous and heterogeneous muscles. By comparing the present data with previously published single-unit studies on the same animals, we confirmed that the whole muscle data provide a weighted ensemble of single-unit effects. They corroborate conclusions based upon single-unit data concerning the proportions of fast- and slow-twitch units, the degree of recovery, and the alteration of force- and speed-related properties of muscle by nerve. In particular, the shape of the whole muscle isometric twitch was a reliable indicator of the relative proportions of fast- and slow-twitch motor units in the muscle. The half-rise time was an indicator of the presence or absence of fast units, and the half-relaxation time was an indicator of the presence of slow units.
Foehring
R C
RC
Department of Neuroscience, University of Florida, College of Medicine, Gainesville 32610.
Sypert
G W
GW
Munson
J B
JB
D000818:Animals; D002415:Cats; D004558:Electric Stimulation; D005260:Female; D007700:Kinetics; D008297:Male; D009046:Motor Neurons / Q000502:physiology; D009119:Muscle Contraction; D009126:Muscle Relaxation; D009132:Muscles / Q000294:innervation* / Q000502:physiology; D009469:Neuromuscular Junction / Q000502:physiology