Determining the activation of antagonist muscles around the knee joint in athletic children can provide useful information for the better understanding of the mechanisms responsible for strength production in athletic populations during developmental ages. The purpose of the present study was to examine possible differences on a) concentric and eccentric isokinetic torque scores of knee muscles and b) electromyographic (EMG) activity of antagonist knee muscle groups during isokinetic concentric and eccentric knee extensions and flexions between prepubertal gymnasts and non-athletic children. Ten gymnasts (age: 9.3 ± 0.8 yrs, training age: 3.4± 1.1 yrs, mass: 30 ± 3.6 kg, height: 132.1 ± 4.6 cm) and ten non-athletic boys (age: 9.1± 0.5 yrs, mass: 28.7 ± 3.4 kg, height: 131.4 ± 3.2 cm) performed maximal concentric and eccentric knee extensions and flexions on an isokinetic dynamometer at 45, 90 and 180°·s
^{-1}
randomly. The torque output of knee extensors and flexors and surface EMG act ivity of vastus lateralis (VL) and biceps femoris (BF) were recorded. The antagonist IEMG values were expressed as a percentage of IEMG of the same muscle when acting as agonist in the same muscle action and angular velocity. ANOVA designs indicated a significant effect of muscle action on the antagonistic IEMG of VL and BF(higher during concentric efforts). An effect of angular velocity was revealed on the antagonistic activity of BF and VL during concentric efforts for both groups. Additionally, no significant difference on the antagonistic activity of knee muscles was found between the two groups examined. The present results suggest that gymnastic training does not affect either torque production or antagonistic activity of knee muscles in boys aged 8--10 years. However, only a longitudinal study could determine possible differences on torque scores and antagonistic activity of knee muscles in gymnasts of various chr onological and training ages.
