Author(s): MOIROUX SAHRAOUI, A., FORELLI, F., SAMOZINO, P., Institution: RAMSAY HEALTHCARE, Country: FRANCE, Abstract-ID: 217

INTRODUCTION:
The force–velocity (F-v) relationship provides a theoretical and practical model to describe the interaction between muscle force and contraction velocity, offering key insights into maximal strength (F₀), maximal velocity (V₀), and maximal power (Pmax). While this concept has been extensively validated in field tests such as jumps and sprints, its application to isokinetic dynamometry remains limited. Establishing valid and reliable F-v profiles from isokinetic testing could enhance the interpretation of neuromuscular function and support individualized rehabilitation and performance strategies. This study aimed to evaluate the validity and intra-session reliability of F-v profiles derived from isokinetic dynamometry
METHODS:
A prospective, cross-sectional, single-center study was conducted at the Orthosport Center (France) between June and August 2025. Twelve healthy, physically active male athletes (mean ± SD: 26.5 ± 3.8 years; 1.81 ± 0.06 m; 76.3 ± 5.9 kg) volunteered to participate. Inclusion criteria comprised a Tegner activity score ≥ 7, Marx Activity Rating Scale ≥ 12, and no history of lower-limb injury or surgery within six months. After a standardized warm-up (10 min cycling at 1.5 W/kg + 3 sets of bodyweight squats), participants underwent concentric isokinetic knee extension and flexion testing on a Humac Norm dynamometer (Athlex, France). Each leg was tested separately at five preset angular velocities (30°, 60°, 180°, 240°, 300°/s). For each velocity, three maximal trials were performed following a submaximal familiarization repetition. Participants were stabilized with straps at the trunk, pelvis, and thigh, ensuring alignment of the knee joint with the dynamometer axis.
Torque–velocity data from the five test conditions were extracted and averaged per limb and muscle group. Individual linear regressions were computed (torque = f(velocity)) in Microsoft Excel to derive F₀ (y-intercept), V₀ (x-intercept = −slope/F₀), and Pmax = (F₀ × V₀)/4. The coefficient of determination (R²) was calculated to quantify model linearity. All analyses were performed separately for quadriceps and hamstrings.
RESULTS:
High linearity of the F-v relationship was observed (mean R² = 0.98 ± 0.02 for dominant quadriceps and 0.97 ± 0.01 for dominant hamstrings). Mean F₀, V₀, and Pmax for the quadriceps were 234.8 ± 31.8 N, 598.7 ± 102.9°/s, and 2418.7 ± 345.8 W, respectively. For the hamstrings, mean F₀ = 178.8 ± 37.9 N, V₀ = 861.7 ± 698.0°/s, and Pmax = 2351.7 ± 972.0 W. ICC values ranged from 0.79 to 0.98 for quadriceps and 0.74 to 0.98 for hamstrings. SEM% values were generally below 10%, and CV values remained acceptable (< 20%) across velocities.
CONCLUSION:
Isokinetic F-v profiling is a valid and reliable method for characterizing neuromuscular performance in healthy athletes. This approach bridges laboratory-based and field-based assessments by integrating mechanical variables into a single framework.