Multivariate isokinetic strength asymmetries of the knee and ankle in professional soccer players

Aim. Soccer players possess various degrees of functional footedness. Their lower limbs are subjected to consistent asymmetrical workloads and neuromuscular adaptations, and as a result develop asymmetrical patterns of musculoskeletal function. This study focused on the myodynamic profile of the knee and ankle joint in professional soccer players. Special emphasis was put on the multivariate quantification of three types of asymmetry: directional (left vs. right), fluctuating (dominant vs. non dominant) and absolute (left vs. right). Methods. One-hundred professional soccer players (mean age 23.4 years, weight 73.3, height 177.6) were tested isokinetically for concentric and eccentric isokinetic muscle strength (1) of the knee flexors and extensors, and (2) of the ankle dorsal and plantar flexors. Knee flexion-extension was tested at 60 degrees, 180 degrees and 300 degrees/s for the concentric mode of contraction and at 60 degrees and 180 degrees/s for the eccentric. The ankle joint was tested only at 60 degrees/s for both the concentric and eccentric action. Results. MANOVA showed significances for all three types of strength asymmetry (joint and action combined): directional (Wilks' Lambda=0.66, F=2.957, P=0.001), fluctuating (Wilks' Lambda=0.611, F=2.957, P=0.007), and absolute asymmetry (Wilks' Lambda=0.47, F=116.26, P=0.000). Several significant asymmetries were also revealed at the univariate level of analysis (P < 0.05). Conclusion. It seems that the lower limbs of professional soccer players are characterized by significant compound muscle strength asymmetries. These findings substantiate the idea of asymmetry in the myodynamic adaptations that take place at the knee and ankle joint of soccer players during the game. Individual modification of the training load, targeting in strength asymmetry correction, should be taken into consideration for injury prevention.