Immediate changes in anticipatory muscle activity after unexpected muscle contraction training

This study aimed to investigate the effects of unexpected trunk muscle contraction training for anticipatory muscle activity during a single‐leg lifting task. A total of 11 healthy adults performed 20 trials of rapid single‐leg lifts by flexing the hip joint of their dominant leg so that the thigh was 90° to the torso. As a training task, participants sat on a rocker board and a sudden movement was initiated to destabilize the trunk muscles. A force plate and 3D motion analysis system determined the motion time, which was from the weight shift onset to the center of mass shift onset. An electromyograph was used to determine the muscle activity onset time and amplitude from both sides of multifidus (MF), internal (IO), and external obliques (EO). The results showed that unexpected muscle contraction training was effective to hasten the stance side of IO muscle onset and decrease the stance side of MF and IO amplitude in a single‐leg lifting task. The stance side of MF and IO has an important role in counteracting the sacroiliac joint shear force in the single‐leg lifting task. Hence, our results indicated that the trunk muscle training improved anticipatory muscle contraction.