Knee extensor electromyography amplitude and trunk flexion are reduced in obese subjects during chair rise performance

Obesity reduces agonist EMG activity during single joint exercises, but the effects of obesity on EMG activity during dynamic activities of daily living are largely unknown. To examine how obesity affects EMG activity during sit-to-stand (STS), an essential daily living task, we measured EMG activity of the medial gastrocnemius (GA), semitendinosus (ST), vastus medialis (VM), and vastus lateralis (VL) and 3D motion analysis in ten lean (L) and 17 obese (O) women completing STS from a chair. STS duration was greater and peak trunk flexion angle was lower in O compared to L. Mean EMG activity of the VM and VL was lower during the anti-gravitational phase II in O. Co-activation of the ST and knee extensors tended to be higher in O. Conclusions: Obesity reduces knee extensor muscle EMG amplitude despite reduced trunk flexion during STS.