Isometric axial rotation of the human trunk from pre-rotated postures

The purpose of this investigation was to study the torque and electromyogram (EMG) in axial rotation from pre-rotated postures. A group of 50 young adults (27 men and 23 women) volunteered for the study. These prepared subjects carried out axial rotation with pre-rotated postures in the direction of pre-rotation and away from it. Torque and EMG were recorded bilaterally from latissimus dorsi, erector spinae at L(3) and T(10) levels, pectoralis, rectus abdominis, external and internal oblique. In 15 degrees pre-rotated posture the axial rotation in the direction of pre-rotation reduced the torque by between 11% and 17% and away from it increased the torque by 12% to 16%. In 30 degrees pre-rotated posture the decrement in torque in the direction of pre-rotation was 24%-33%, and in the opposite direction the gain was between 21% and 32%. Even with decreased torque with rotation in the pre-rotation direction the EMG increased up to 123%. The EMG magnitude and slopes of EMG in these activities demonstrated significant increases while in the opposite direction slight decreases were observed. The EMG of each muscle was significantly different from all other muscles ( P<0.001). A significant ( P<0.01) but low correlation between EMG and torque was obtained. Significant linear regressions between torque and EMG of different muscles were obtained ( P<0.01; r=up to 0.70).