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Background  Many studies have investigated isokinetic performance in volleyball players but not through surface maps.    Objectives  The goals of this study were to assess velocity-specific isokinetic knee extensor–flexor muscle strength and to compare the isokinetic knee extensor–flexor muscles between professional (PRO) and under-17 (U17) female volleyball players.    Method  This cross-sectional laboratory study was developed with two groups: PRO ( n  = 12), median age  = 21.3 years, and U17 ( n  = 9), median age  = 15 years. Peak torque, total work, mean power, angle of peak torque, hamstring–quadriceps torque ratio (H–Q ratio) and torque–angle–velocity surface maps were analysed from knee extension–flexion at 60, 120 and 300 degrees per second (°/s).    Results  Significant differences were identified for extensor peak torque between PRO   x   = 202.3 Newton metre (N·m) (standard deviation [SD] = 24.4) and U17   x   = 141.6 N·m (30.1) at 60 °/s ( p  < 0.001;   d   = 2.21) as well as flexor peak torque (PRO   x   = 75.7 N·m [10.3] and U17   x   = 57.7 N·m [11.4]) at 120 °/s ( p  < 0.001;   d   = 1.65) for the dominant limb. There were also significant group differences for total work and mean power at all velocities for extension and flexion. Surface maps demonstrated higher torque at lower speeds for both groups with smaller torque changes across velocities for flexion.    Conclusion  Different groups of female volleyball players showed contrasting concentric knee muscle strength across isokinetic velocities.    Clinical implications  These results demonstrate the importance of specific strength training for different age groups, even within the same sport, and provide insight into muscle strength.

Velocity-specific knee strength between professional and under-17 female volleyball player