Document Type : Original research papers
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. 12 male powerlifters performed leg-press movement while the backrest of leg-press machine was adjusted at 15°, 20°, 25°, and 30° 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 15°, 20°, and 25° compared to 30° backrest position. VM showed greater activity at 20° and 25° compared to 30°. VL showed greater activity at 20° and 25° compared to 30°. It was also more active at 20° than at 25° of backrest position. The ST and BF were more active at 20° compared to other positions. There was a slight co-contraction ratio difference at 20°-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 45-degree leg-press machine, the backrest of the machine be adjusted at a 20° angle with the feet placed at the top of the foot-plate.