Journal of applied physiology | 2019
MOTOR UNIT DISCHARGE RATE AND THE ESTIMATED SYNAPTIC INPUT TO THE VASTI MUSCLES IS HIGHER IN OPEN COMPARED TO CLOSED KINETIC CHAIN EXERCISE.
Abstract
PURPOSE\nIt has been suggested that closed kinetic chain exercises may induce more balanced activation of vastus medialis (VM) and lateralis (VL) compared to open kinetic chain exercise. This study aimed to 1) compare between-vasti motor unit activity and 2) analyze the combined motor unit behavior from both muscles between open and closed kinetic chain exercises.\n\n\nMETHODS\nThirteen participants performed isometric knee extension and leg press at 10,30,50,70% of the maximum voluntary torque. High density surface EMG was recorded from the VM and VL and motor unit firings were automatically identified by convolutive blind source separation. We estimated the total synaptic input received by the two muscles by analyzing the difference in discharge rate from recruitment to target torque for motor units matched by recruitment threshold.\n\n\nRESULTS\nWhen controlling for recruitment threshold and discharge rate at recruitment, the motor unit discharge rates were higher for knee extension compared to the leg press at 50% (estimate=1.2 pps, standard error (SE)=0.3 pps, P=0.0138) and 70% (estimate=2.0 pps, SE=0.3 pps, P=0.0001) of maximal torque. However, no difference between muscles were detected in both exercises. The estimates of synaptic input to the muscles confirmed these results.\n\n\nCONCLUSION\nThe estimated synaptic input received by VM and VL was similar within and across exercises. However, both muscles had higher firing rates and estimated synaptic input at the highest torque levels during knee extension. Taken together, the results show that open kinetic chain knee extension is more suitable for increasing the concurrent activation of the vasti muscles.