Abstract
Muscles not only have a contractile function, but also a viscous elastic property. This property is observed in response to stretching the contracting muscle. The purpose of this study is to investigate the relationship between stretch-evoked torque and the conditions before stretching (contraction level, velocity and length) the flexor pollisis longus muscle (FPL). The subjects sat on a chair, and their left hands were affixed to the apparatus. Then, they were instructed to track the target force of FPL displayed on the monitor, and to keep isotonic contraction (7 to 35% of the maximum voluntary contraction (MVC) by slowly stretching at an angular velocity V1 (3 to 13 deg/s). After 2 s, a small ramp stretch (300 deg/s) was applied to the thumb from various angles (7 to 27 deg). The angle, flexing torque of the thumb, and electromyogram (EMG) of the FPL were measured. In the same way, the passive torque was measured in response to the length perturbation at a resting state. Each measurement was carried out ten times. The stretch-evoked torque was estimated by subtracting the passive torque and isotonic torque from the observed torque. As a result, the stretch-evoked torque increased as the contraction level and angular velocity (V1) increased, but the stretch-evoked torque decreased as the length of the FPL increased. In conclusion, it was shown that the viscoelastic property of the muscle changed not only in accordance with the muscle activation level, but also in accordance with velocity (V1).
