Comparison of two classification criteria of lateral strength asymmetry of the lower limbs in professional soccer players

Abstract

Prospective studies have indicated that assessing muscle function by the isokinetic test in the preseason is able to identify muscle strength variables that can be associated with injuries in the hamstring muscles of professional soccer players. However, the results are conflicting and could be related to the different cutoff points for the categorization of athletes in asymmetric or symmetric. Based on these conflicting results, the present study aims to: i) Identify the cutoff points of lateral asymmetry (LA) of the 95% confidence interval for the peak torque in soccer players, evaluated by the isokinetic test, taking into consideration the mean population value; ii) Compare LA between 15% cutoff point proposed in literature and the upper limit of 95% confidence interval (UP) of the study population. Sixty-four professional soccer players performed five knee flexion and extension repetitions at rate of 60°/s, with a one-minute interval. To determine the cutoff point for strength asymmetries, the UP was used, and for the purpose of diagnostic concordance of information among the different values, the McNemar’s ?² test was applied. The proportion between symmetric and asymmetric athletes was not different from the 15% cutoff point and the general population, both for knee flexors (?² = 0.5, p = 0.250) and the knee extensors (?² = 2.0, p = 0.125). It was concluded that the cutoff point of 15% referenced in literature for the general population provides similar diagnostic information for the classification of professional soccer players.