RELATIONSHIP BETWEEN THE TWITCH TENSION CURVE AND DISCHARGE PATTERN IN SINGLE HUMAN MOTOR UNITS / 体力科学

ABSTRACT

In this study, the relationships between the contractile properties of human motor units and their discharge patterns, characteristics of recruitment and others were examined. Action potentials of single human motor units in<I> m, extensor digiterum</I>were detected by use of an inserted electrode. Tension curves of single motor units were recorded under the conditions that tension in finger extension was gradually increased, and that the subject relaxed his muscle as soon as he observed a sweep on a Braun tube triggered by the action potential of a single motor unit. About 100 twitch tension curves were summed up to obtain the average tension curve of a single motor unit. The τ-S diagrams were obtained from the mean discharge intervals (τ) of motor units at various sustained tensions and their standard deviations (S) . The λ values were also obtained from the relation F<SUB>th</SUB> (-T<SUB>1</SUB>G) =ρG<SUP>λ</SUP>.<BR>It was observed that the contraction time of the twitch tension curve of single human motor unit in a muscle was nearly proportional to τs (the τ values at a constant S value) . We presume that the regularity of discharging of motor unit affects the contraction speed in human muscle, because the motor unit with more regular discharging has longer contraction time of twitch.