Background: The relationship between muscle injury and strength disorders remains a matter of controversy.
Purpose: Professional soccer players performed a preseason isokinetic testing aimed at determining whether (1) strength variables
could be predictors of subsequent hamstring strain and (2) normalization of strength imbalances could reduce the incidence
of hamstring injury.
Study Design: Cohort study (prognosis); Level of evidence, 1.
Methods: A standardized concentric and eccentric isokinetic assessment was used to identify soccer players with strength
imbalances. Subjects were classified among 4 subsets according to the imbalance management content. Recording subsequent
hamstring injuries allowed us to define injury frequencies and relative risks between groups.
Results: Of 687 players isokinetically tested in preseason, a complete follow-up was obtained in 462 players, for whom 35 hamstring
injuries were recorded. The rate of muscle injury was significantly increased in subjects with untreated strength imbalances
in comparison with players showing no imbalance in preseason (relative risk = 4.66; 95% confidence interval: 2.01-10.8). The risk
of injury remained significantly higher in players with strength imbalances who had subsequent compensating training but no
final isokinetic control test than in players without imbalances (relative risk = 2.89; 95% confidence interval: 1.00-8.32).
Conversely, normalizing the isokinetic parameters reduced the risk factor for injury to that observed in players without imbalances
(relative risk = 1.43; 95% confidence interval: 0.44-4.71).
Conclusion: The outcomes showed that isokinetic intervention gives rise to the preseason detection of strength imbalances, a
factor that increases the risk of hamstring injury. Restoring a normal strength profile decreases the muscle injury incidence.
Keywords: strength imbalance; hamstring; injury; prevention; soccer