The efficacy of angle-matched isokinetic knee flexor and extensor strength parameters in predicting agility test performance

Background: Agility is a fundamental performance element in many sports, but poses a high risk of injury. Hierarchical modelling has shown that eccentric hamstring strength is the primary determinant of agility performance. Hypothesis/Purpose: To evaluate the predictive potential of angle-matched knee flexor and extensor strength parameters on a battery of agility tests. Study Design: Controlled laboratory study. Methods: Nineteen intermittent games players completed an agility battery and isokinetic testing of the eccentric knee flexors (eccH) and concentric knee extensors (conQ) at 60, 180 and 300°•s-1. Peak torque and respective joint angle were calculated for eccH and conQ at each speed. Dynamic control ratios (eccH:conQ) and fast:slow ratios (300:60) were calculated using peak torque values, and again using angle-matched data. The agility test battery distinguished linear vs directional changes and prescriptive vs reactive tasks. Results: Linear regression showed that eccH parameters were generally a better predictor of agility performance than conQ parameters. Stepwise regression showed that only angle-matched strength ratios contributed to the prediction of each agility test. Trdaitionally calculated strength ratios using peak torque values failed to predict performance. Angle-matched strength parameters were able to account for 80% of the variation in T-test performance, 70% of deceleration distance, 55% of 10m sprint performance, and 44% of reactive change of direction speed. Conclusions: Traditionally calculated strength ratios failed to predict agility performance, whereas angle-matched strength ratios featured in a predictive stepwise model for each agility task had better predictive ability. Levels of Evidence: 2c. Clinical Relevance: A combination of strength parameters is required to predict agility performance, and the strength of the correlation is task dependent. Angle-matched isokinetic data is advocated when profiling for athletic performance.