Limited Predictive Value of Concentric Knee and Trunk Isokinetic Peak Torque for Maximal Force and Stretch-Shortening Cycle Performance in Highly Trained Youth Optimist Sailors.

Background: Concentric knee and trunk strength may contribute differently to maximal force and stretch-shortening cycle performance in youth sailors. This study evaluated the predictive value of concentric knee and trunk isokinetic strength for these outcomes in highly trained youth Optimist sailors. Methods: Forty highly trained Optimist sailors (20 boys and 20 girls; age, 13.03 ± 1.40 years) completed knee and trunk isokinetic testing at 60°·s-1 and 180°·s-1, isometric mid-thigh pull, squat jump, and countermovement jump tests. Velocity-specific multiple linear regression models included a composite of dominant and nondominant knee extensor and flexor strength, trunk extensor strength, trunk flexor strength, and sex. Results: The models explained 60.7% and 49.4% of the variance in isometric mid-thigh pull peak force at 60°·s-1 and 180°·s-1, respectively. The knee strength composite was independently associated with peak force at both velocities (β = 0.51, p = 0.003; β = 0.56, p = 0.006). The models explained 1.3-3.5% of dynamic strength index variance and 17.8% and 4.5% of eccentric utilization ratio and elastic index variance at 60°·s-1 and 180°·s-1, respectively. Trunk flexor strength was associated with eccentric utilization ratio and elastic index at 60°·s-1 (β = 0.52, p = 0.029), although these outcomes are mathematically dependent. Sex was not associated with any outcome. Conclusions: Concentric isokinetic strength showed greater predictive value for maximal force than for stretch-shortening cycle performance. Combined knee extensor and flexor strength was consistently associated with maximal force, whereas limited variance was explained in stretch-shortening cycle outcomes.