Are Eccentric Strength Asymmetries Connected with Increased Risk for Muscle Injuries in the Thigh Muscles of Professional Soccer Players?

Introduction. The purpose of this prospective study was to statistically evaluate the relation between isokinetic strength asymmetries and risk of non-contact muscle strains in soccer. Methods. One hundred professional soccer players (age 23.4±4.8 years, height 178±6.7 cm, body mass 74.2±7.6 kg) were tested for isokinetic concentric and eccentric strength during the extension and flexion of the knee and ankle joint. Isokinetic testing was carried-out concentrically at 60o /sec. 180o/sec & 300o/sec and eccentrically at 60o/sec & 180o/sec for the knee joint. The ankle joint was tested at 60o/sec for both the concentric and eccentric mode of action. Each players' non-contact muscle strains resulting in missing at least one practise session or game were recorded during one competition season. Results. Analysis of the composite muscle strength asymmetries showed a significantly high relative risk of injury for players with eccentric strength asymmetries greater than 15% (RR=5.10; 95% CI: 1.29-20.17). ?he majority of muscle strains involved 16% the hamstrings and 7% the quadriceps. The relative risk for strains in knee extensors strains was significantly increased in players with eccentric muscle asymmetries >15% (RR=1.93, 95% CI: 0.81- 4.56) and approximated statistical significance in the case of knee flexors strains (RR=1.82, 95% CI: 0.86-3.87). No significant relationship was found between concentric muscle strength asymmetries and muscle strains. Conclusions. Players with eccentric isokinetic strength asymmetries higher than 15% were more prone to injure their lower extremities. Preseason eccentric isokinetic assessment is required for the identification of soccer players being at high risk of thigh muscle strain and for the prevention of potential muscle strains via individualized exercise protocols. [ABSTRACT FROM AUTHOR]