Isokinetic Strength of Knee Flexors and Extensors in Very Young Soccer Players

Abstract

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 nondominant 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. ResultsThe 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).

Isokinetic strength of knee flexors and extensors of adolescent soccer players and its changes based on movement speed and age

“…This trend was also confi rmed by Dvir and David (1996); Lehance et al (2009) ;Malý, Zahálka and Malá (2010); Kellis et al (2001). These authors explain this decrease by the fact, that, at high speed levels, muscle contraction is accomplished only by a fraction of the muscle fi ber, mostly that muscle fi ber, which ismorphologically adapted to high speed work.…”

Unilateral and Ipsilateral Strength Asymmetries in Elite Youth Soccer Players With Respect to Muscle Group and Limb Dominance

“…Rahnama et al (2005), suggested that up to 68 % of soccer players had muscle asymmetries in extensors or flexors between the extremities of higher than 10 % in at least one of the measurements of muscle strength. Muscle bilateral asymmetries were found in at least one measurement in 50 % of players at a velocity of 60 °·s -1 and in 75 % of players at a velocity of 300 °·s -1 (Maly et al, 2010).…”

Power assessment of lower limbs and strength asymmetry of soccer goalkeepers

“…More attention should be paid to individuals whose difference between the limbs is > 15% (Croisier et al, 2003;Malý, Zahálka, & Malá, 2010;Menzel et al, 2013). Occurrence of muscle asymmetry may be a result of insufficiently compensated physical activity, inadequate or incomplete rehabilitation programme, muscular strength imbalance between agonist and antagonist, long-term unilateral load (preferring) of one limb.…”

“…Although asymmetrical strength has been linked to a variety of pathological conditions or risk of injuries in field soccer players (Dauty & Potiron-Josse, 2004;Rahnama, Lees, & Bambaecichi, 2005;Rahnama, Reilly, Lees, & Graham-Smith, 2003;Tourny-Chollet, Leroy, Leger, & Beuret-Blanquart, 2000), no research results are available in terms of identification of strength imbalances during power assessment in elite soccer goalkeepers, who often prefer one leg to kick (kicking leg) and another to take-off (jumping leg). Lower limb bilateral strength asymmetries in soccer are the most frequently assessed using the isokinetic dynamometry method (Cometti, Maffiuletti, Pousson, Chatard, & Maffulli, 2001;Kellis, Gerodimos, Kellis, & Manou, 2001;Lehnert, Urban, Procházka, & Psotta, 2011;Malý, Zahálka, & Malá, 2010) but Menzel et al (2013) suggest, based on results of factors analysis (forty-six elite Brazilian soccer players), that the isokinetic testing and CMJ tests are widely independent methods for assessment of bilateral differences. Due to the above specified manifestation of goalkeeper's movement (jump), with the principle of high acceleration, jump testing can be considered more adequate than isokinetic strength where the movement speed is constant.…”