- - - Department of Sport Biomechanics, Faculty of Sports Sciences, Bu Ali Sina University, Hamedan, Iran
- - - Department of Sport Biomechanics, Faculty of Sports Sciences, Bu Ali Sina University, Hamedan, Iran
- - - Department of Sports Biomechanics, Faculty of Sports Sciences, Shahid Bahonar University of Kerman, Kerman, Iran.

The purpose of this study was to determine the effects of trunk and foot positions on electromyographic activity and co-contraction of selected lower extremity muscles during leg-press resistance training. ۱۲ male powerlifters performed leg-press movement while the backrest of leg-press machine was adjusted at ۱۵°, ۲۰°, ۲۵°, and ۳۰° angles relative to the horizon. The feet were placed in three different positions namely, top, middle, and bottom of the foot-plate. Electromyography activity of the rectus femoris (RF), vastus medialis (VM), vastus lateralis (VL), biceps femoris (BF), and semitendinosus (ST) muscles were recorded while performing leg-press task at different trunk-feet conditions. The muscle co-contraction at the knee joint was also calculated. When the feet were placed on top of the foot-plate, RF had greater activity at ۱۵°, ۲۰°, and ۲۵° compared to ۳۰° backrest position. VM showed greater activity at ۲۰° and ۲۵° compared to ۳۰°. VL showed greater activity at ۲۰° and ۲۵° compared to ۳۰°. It was also more active at ۲۰° than at ۲۵° of backrest position. The ST and BF were more active at ۲۰° compared to other positions. There was a slight co-contraction ratio difference at ۲۰°-tap degrees condition compared to other conditions. According to the results, it is recommended that, for the recruitment of more motor units when using the ۴۵-degree leg-press machine, the backrest of the machine be adjusted at a ۲۰° angle with the feet placed at the top of the foot-plate.

Leg-Press, Electromyography, Co-contraction, Foot Position, Trunk Position