Passive repetitive loading of the lumbar tissues influences force output and EMG during maximal efforts

Loading of the low back tissues induces tension-relaxation in the viscoelastic connective tissues. The extent to which repetitive loading influences the muscle activation and subsequent muscle force production has not been fully explored. The purpose of this study was to examine the myoelectric activity of the trunk muscles during maximal flexion and extension exertions before and after a passive trunk flexion–extension protocol. Nineteen subjects performed three trials of maximal efforts in trunk flexion and extension while seated in an upright position. Surface electromyography (EMG) recordings were collected bilaterally from paraspinal (thoracic, TP, lumbar LP), rectus abdominis (RA), and external oblique muscles. A 10-minute passive trunk flexion–extension protocol was used to repetitively load the lumbar tissues at a rate of 0.17 rad/s, through the subjects’ range of motion. The main findings included a significant reduction in moment output during extension efforts ( p