The aim of this study was to determine whether there are differences in the fatigability of plantar flexor muscles during sustained submaximal contractions in prepubertal boys and girls. Fifteen boys (age 10.0 +/- 1.0 years) and 15 girls (age 9.8 +/- 0.9 years) participated in the study. The fatigue protocol consisted of a 10 min isometric plantar flexion at 20% of the maximal voluntary contraction. Immediately after this, five maximal isometric contractions were performed with a 3 min interval between contractions. During the experiment, electromyograms of the agonist muscles soleus and medial gastrocnemius and antagonist tibialis anterior were recorded. We observed no differences between the sexes (P < 0.05) in the decrease in torque or in the recovery rate after the fatigue protocol. Nor were there any differences between the sexes (P < 0.05) in agonist or antagonist muscle activation during the fatigue protocol and recovery period. The results indicate that there are no differences in fatigability between prepubertal boys and girls during submaximal sustained contractions, probably because the agonist and antagonist muscles were activated similarly in both sexes.