ABSTRACT
Introduction Muscular strength is one of the most important components of physical performance in soccer, in terms of both high-level performance and injury occurrence. one essential function of the muscles is to protect and stabilize joints of the skeletal system. In soccer, the players are forced to switch between high demanding skills which require strength, power, coordination and agility, with these qualities being symmetrically distributed to the lower extremities for maximal body balance and skill efficiency (Fousekis et al., 2010). long-termed preferred and uncompensated load of one side of the body may lead to asymmetry and dominance of one leg, what can be a result of pre-existing limb preference (footedness). It has been documented that strength asymmetry across the body can be linked to increased prevalence of injury (Croisier et al., 2008; McCall et al., 2014) and impaired performance in athletes (Young et al., 2002). Results of the study by Fousekis et al. (2010) suggest that long-term training in soccer causes strength asymmetries of different characters and degrees. Out of 100 professional players tested, only 11 percent did not show strength asymmetry in 14 examined parameters. In contrast, up to 20 percent showed four to seven strength asymmetries. Tol et al. (2014) include data on a sample of 52 professional soccer players after hamstring injury in which the injured leg was compared with uninjuredleg;67percentoftheclinicallyrecoveredhamstringinjurieshadatleast onehamstringisokinetictestingdeficitoftheipsilateralleg.Thestudyby lehance et al. (2009), which examined muscle strength on an isokinetic dynamometer in the preparatory period in elite soccer players (n = 57), showed that up to 56 percent of the players were at risk of muscle strength imbalances of knee flexorsorextensors.Theauthorspresentahigherproportionofmusclestrength imbalances in young soccer players in comparison to senior players. This data may suggest that isokinetic strength assessment should become an integral part of a player’s diagnostics before the preparatory period aimed at detection of the level of strength predispositions as well as knee extensor and flexor asymmetries (Croisier et al., 2005). It seems that a high level of the ratio of hamstring and quadricepsmusclestrengthisanessentialparameterofidentificationofincreased risk of injury (Fousekis et al., 2010).
