This study investigated the characteristics of force and power outputs during the trunk-twist exercise accompanying stretch-shortening cycle (SSC) movement focusing on the effect of SSC movement under different loads. Twenty healthy male college students who habitually exercised performed the bar twisting exercise. To investigate the effect of SSC on trunk-twist, participants performed the exercise using SSC (SSC condition) or without SSC (CON condition). For the SSC condition, participants rotated the bar clockwise; when the right side of the bar passed the mark (located at a bar angle of -75°), participants immediately rotated the bar counterclockwise. For the CON condition, the participants rotated the bar counterclockwise from the mark without using SSC movement. Three loads (0 kg, 10 kg, and 20 kg) were used under both conditions. Kinematic and kinetic data were calculated using data recorded with a motion capture system (250 Hz) and force platforms (1,000 Hz). The surface electromyograms (EMG) of 8 trunk muscles were recorded. The results of the analyses were as follows:
The trunk-twist torque and torque power under the SSC condition were significantly higher than those under the CON condition. Also, the SSC movement contributed to an increase in the peak angular velocity of the bar and trunk-twist, and shortened the time until the bar reached its peak angular velocity. The activity of the external oblique and latissimus dorsi, which are the agonist muscles used for the trunk-twist under the SSC condition, was significantly larger than under the CON condition. The activity of these muscles increased before the bar rotated counterclockwise, and contributed to an increase in the trunk-twist torque and torque power.
The angular velocity of the bar and trunk-twist decreased with increasing load. Meanwhile, the trunk-twist torque and torque power at 0 kg were highest. The EMG of the trunk-twist muscles showed no significant difference with increasing load.
These results suggest that using SSC movement during the trunk-twist exercise increases the force and power output of the trunk-twist, and that the latter decrease when the moment of inertia of the bar exceeds 10.36 kgm2.
