In this cross-sectional study, the differences in the isokinetic peak torque of the knee joint muscles (dominant and non-dominant) were investigated in three groups of youths (n=45; age, 14.9+/-1.1 years) with different soccer training backgrounds. Significant main effects were observed for training background on the functional hamstrings to quadriceps ratios for knee flexion (H(CON):Q(ECC) ratio; F(2,42)=4.023, P=0.025) and extension (H(ECC):Q(CON) ratio; F(2,42)=8.53, P<0.001) at 4.32 rad/s. Post hoc tests indicated that both ratios were significantly different between conventionally trained players compared with resistance-trained players and controls (mean+/-SD; H(ECC):Q(CON) ratio, dominant limb; 0.91+/-0.10; 1.04+/-0.12; 1.10+/-0.22; non-dominant limb; 0.89+/-0.09; 1.05+/-0.19; 1.06+/-0.15; H(CON):Q(ECC) ratio, dominant limb; 0.36+/-0.06; 0.34+/-0.07; 0.30+/-0.08; non-dominant limb; 0.33+/-0.05; 0.32+/-0.08; 0.28+/-0.07). Results suggest that the muscle-loading patterns experienced in youth soccer may alter the reciprocal balance of strength about the knee under high-velocity conditions. The findings also indicate that these balances may be improved by incorporating resistance training into the habitual exercise routines of youth soccer players.