Muscular imbalance and acute lower extremity muscle injuries in sport

Investigating factors associated with muscle strains highlight the multifactorial origin of the injury and the difficulty of identifying isolated or combined factors that caused the injury. Among the numerous causes reported in the literature, only a few have been scientifically associated with injury occurrence, while others have been empirically suggested. Contradictions in articles dealing with muscle strength and imbalance are frequent, and are probably the result of differences in methodology and criteria for patient inclusion. Imbalance in muscle strength commonly refers to abnormal bilateral asymmetry (between homologous groups) and a disruption of the agonist-antagonist ratio. Some authors who focus on a history of hamstring or adductor strains have demonstrated the frequent abnormality of muscle strength and balance by means of isokinetic assessment. Mixed ratios, combining the eccentric performance of “decelerating” muscles (such as the hamstrings) and the concentric performance of “mobiliser” muscles (such as the quadriceps) are suggested and seem relevant. An increased emphasis on eccentric strengthening exercises, particularly for the hamstrings, and ratio correction on the basis of statistically selected cut-offs, significantly reduces the recurrence rate of the injury and lingering complaints upon return-to-sport. Similarly, isokinetic interventions, as a preseason screening tool in sports where there is a high rate of muscle strain injuries, could detect imbalances early and thus promote a preventive strategy.