Coordination among thigh muscles including the vastus intermedius and adductor magnus at different cycling intensities

Although many studies have been focused on muscle synergies in the lower limbs, synergies of the thigh muscles during cycling have not been investigated in detail. We examined synergies of the thigh muscles including the vastus intermedius (VI) and adductor magnus (AM) while cycling. Eight healthy men pedaled at 20%, 40%, 60%, 80% and 100% of maximal aerobic power output at a constant cadence of 60 rpm. Surface electromyography (EMG) recorded signals from the deep VI and the three superficial quadriceps femoris (QF) muscles, the two hamstrings and the AM. The root mean square of the EMG signal was averaged every 2° of crank rotation and normalized by the peak value for each muscle. We used factor analysis to assess normalized EMG recordings while cycling and to identify thigh muscle synergies. The VI, the superficial QF muscles and the AM dominated the first muscle synergy at all power output levels. The AM also formed a second synergy with the two hamstrings at all power output levels. These results suggest that the VI coordinates with the other QF and AM muscles, and that the AM coordinates with the QF and hamstring muscles while cycling.