疲労困憊に至る伸張-短縮サイクル運動が下腿三頭筋の収縮特性及び損傷指標に及ぼす影響

The repeated heel-raiseis a typical stretch-shortening cyc1e (SSC) exercise. The exercise is not only performed in resistance training but also used for evaluating muscular strength in c1inical settings. The present study was undertaken to investigate the effect of repeated heel-raise exercise to a volitional exhaustion on contractile properties of the triceps surae muscle and parameters reflecting muscle injury.
Five Healthy university students with no orthopedic disorders served as subjects. Each subject performed two exercises. ln SSC condition，the subjects repeated the SSC exercise every 2 seconds to volitional exhaustion. ln the IS0 condition，they repeated the same number of an isometric exercise as that of the SSC exercise.
In the SSC condition，the subjects exhausted after repeating the exercise 28.6 times. At exhaustion，maximal torque developing capacity decreased significantly and the decrease was accompanied by a tendency of a lower median power frequency of the EMG signals. A significantly higher lactate concenlration was also observed. On the other hand，the ISO exercise induced no significant changes in these parameters.
In the SSC condition，the decreased maximal torque developing capacity at exhaustion remained one hour and even one day following the exhausting exercise. The circumference of the lower extremity became larger significantly at exhaustion as compared with the pre-exercise values and remained higher one hour and one day after the exercise. The pressure threshold for pain in the medial head of the gastrocnemius muscle and the muscle-tendon junction of the triceps surae muscle became significantly
lower compared with pre-exercise value one hour or one day following the exercise. Muscle pain
evaluated using visual analog scale f1uctuated and the higher value was observed at exhaustion and one day after SSC exercise. ln the ISO condition，no significant changes in these parameters were observed.
The results of the present study indicated that the SSC exercise had more profound effects on
contractile properties， myo-electrical signals and injury-related parameters than the ISO exercise.
Furthermore, the results suggest that，even in a relatively small number of repetitions，repeated heel-raise, at ypical SSC exercise，induces as light muscle injury.