Reliability of a Standardized Isokinetic Knee Strength Protocol Across a Slow-Fast Velocity Spectrum in Physically Active Adults with the Biodex System 4 Pro.

Background: Isokinetic dynamometry is widely used to assess knee muscle strength in both clinical and athletic settings; however, the reliability of measurements across different angular velocities representing distinct regions of the force-velocity spectrum requires further investigation.

Purpose: To examine the test-retest reliability of concentric isokinetic knee extension and flexion strength at slow and fast angular velocities using the Biodex System 4.

Study design: Repeated measures.

Methods: A total of 15 healthy, physically active adults, women (n=7) and men (n=8), within the age range 21-34 years (inclusion criterion: 18-40 years) participated in the study. Each subject completed two test sessions spaced one week apart. Peak torques of the dominant leg during knee extension and flexion were measured using the Biodex System 4 at angular velocities of 90°/s and 180°/s. Reliability was analyzed using intraclass correlation coefficient (ICC) with 95% confidence intervals and the coefficient of variation (CV).

Results: The

results showed high to very high reliability across all test conditions (ICC = 0.92-0.99; 95% CI: 0.78-1.00). CV values ranged from 2.7% to 4.2%, and no significant differences in peak torque were observed between test sessions.

Conclusion: The isokinetic measurements were reliable at both 90°/s and 180°/s, supporting their use in rehabilitation and strength training evaluations. As distinct strength qualities exist and muscle performance can be assessed across a dynamic velocity spectrum, isokinetic testing at multiple angular velocities may provide a more comprehensive characterization of muscle function than a single-speed assessment alone. Level of evidence 2.