The purpose of this study was to examine if a fatigue task of agonist muscles also causes fatigue to the antagonist muscles. Fourteen(n = 14) healthy males (age: 24.3 ± 2.5 y) participated in two isokinetic fatigue protocols (IFPs) at the angular velocity of 60°/s. The motion ranged from 0° to 90° of knee flexion. The first protocol consisted of 25 concentric maximal trials. The second protocol consisted of 60 concentric submaximal trials with a resistance equal to 60% of the maximum isokinetic torque exerted at 60°s
$^{-1}$
. The muscles selected for EMG recording were Vastus Medialis (VM) and Vastus Lateralis (VL) as agonists and Biceps Femoris (BF) as antagonist. Both protocols were performed with isolated extensions. However, reciprocal maximal knee extension-flexion trials were performed periodically for the estimation of torque and EMG activity of BF muscle. The obtained results indicate that both protocols cause a significant decrease of torque and EMG activity of the agonist muscles. On the contrary, they did not affect the torque and EMG activity of the antagonist muscle. Thus, it can be assumed that antagonist muscles are not fatigued during a fatigue task and they are regulated mainly by central neuronal mechanisms.
