[in Japanese]

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[in Japanese]

View full abstract

[in Japanese]

View full abstract

[in Japanese]

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[in Japanese]

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We validated the evaluation of muscular endurance in human beings during submaximal contraction using twitch interpolation and surface electromyography (EMG). Subjects were 14 healthy males. Seven healthy men randomly exerted 20, 40, 60, 80, and 100% maximum voluntary contraction (MVC) of isometric abductions in the left first dorsal interosseous muscle. Simultaneously with voluntary contractions, the ulnar nerve was stimulated percutaneously at supramaximal intensity. Voluntary activation was calculated based on the relationship between voluntary and twitch forces, indicating the degree of motor unit recruitment (twitch interpolation). Physiological MVC excluding psychological factors was calculated based on 100% voluntary activation. Ordinary (psychological) MVC was smaller than physiological MVC in three subjects, indicating the inability of their motor units to activate fully. Subjects revised MVC using twitch interpolation (revised MVC group, n=7) and no revision (control group, n=7) exerting isometric abduction of 60% MVC until exertion. Endurance time during the fatigue task was significantly shorter in the revised MVC group than in the control group (p<0.01). Endurance time also varied less in the revised MVC group. Median frequency (MDF) of surface EMG detected from FDI decreased significantly during fatiguing contractions in both groups. (p<0.01). Although the variation in endurance time decreased, the variation of change in MDF increased in the revised MVC group, possibly reflecting absolute endurance in individuals. These results suggest that absolute endurance during voluntary contraction in human beings can be evaluated using physiological MVC, endurance time, and patterns in surface EMG changes.

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