Background Monitoring of physical fitness characteristics in very young players could be helpful for the selection of talented youth or identification of the strengths and weaknesses in motor predispositions for physical performance. Muscular strength tested on an isokinetic dynamometer belongs to the most widely used methods of the identification of knee extensors (KE) and flexors (KF) strength in adult soccer players It appears that there is the lack of information concerning monitoring of isokinetic strength of lower limbs and its parameters in very young soccer players. The purpose of the study was to find out the level of isokinetic strength (IS) of KE and KF and to compare the selected characteristics of IS related to the movement velocity and limb dominancy in very young players.

Methods Young players (n=16, age 8.8±0.4 years, body height=137.5±6.2 cm, body weight=30.7±4.1 kg) were tested on an isokinetic dynamometer Cybex Humac Norm. Maximum peak muscle torque (PT) of KE and KF, their mutual ratio (H:Q) and bilateral ratio between Q:Q or H:H were assessed during concentric contraction at different velocities (60,180,300°.s-1) in the dominant leg (DL) and non-dominant leg (NL). Mixed-design ANOVA was used for evaluation of PT differences between the factors (angular velocity, limb dominancy, muscle groups–KE, KF). For multiple comparisons we used Bonferonni's post-hoc test. Statistical significance was set at p≤0.05. Effect size was assessed using the ηp2 coefficient.

Results The results of PT during 60,180 and 300°.s-1 were (KE [DL]: 60.9±11.6, 39.2±7.3, 30.9±5.4 N•m, [NL]: 60.8±12.2, 41.1±7.8, 33.6±6.3 N•m and for KF [DL]: 34.5±6.2, 24.5±4.1, 19.7±4.3 N•m, [NL]: 33.2±5.7, 24.6±5.8, 20.0±4.8 N•m). Movement velocity had a significant effect on the level of PT (peak torque) in the players F(1.3, 77.9)=414.9, p<0.01, ηp2=0.874 and HQ ratio (F(1.7, 49.8)=7.6, p<0.01, ηp2=0.202. With increasing velocity, significant differences were revealed in PT (L vs M, L vs H, M vs. H p<0.01) and HQ ratio (L vs M, L vs H p <0.05).

Limb dominancy did not significantly influence the level of PT F(1, 60)=0.180, p>0.05, ηp2=0.687 or H:Q F(1, 30)=0.760, p>0.05, ηp2=0.025.

Movement velocity and limb dominancy did not have any significant effect on the bilateral ratio between QQ and HH in young soccer players (p>0.05).

Conclusion The results indicated significant differences in PT and HQ in relation to movement velocity. On the contrary, no significant differences were found in bilateral ratio (Q:Q, H:Q). Limb dominancy did not significantly affect any of the observed characteristics. The presented data may contribute to comparison or establishment of standards for strength profile in this age category. Supported by GAČR P407/11/ P704 and MSM 0021620864.