Background: Knee osteoarthritis (KOA) is a progressive degenerative disease that negatively affects mobility and quality of life in middle-aged and older adults. Neuromuscular deficits, including impairments in muscle strength, structure (atrophy), and quality (fatty infiltration) are commonly reported in people with KOA. However, the relative contribution of these specific neuromuscular characteristics to functional performance is not fully understood. Identifying which muscle parameters best predict functional outcomes is essential for tailoring targeted and effective rehabilitation protocols.

Objectives: To investigate the relationship and the predictive value of quadriceps and hamstring maximal strength, muscle architecture (thickness), and muscle quality (echo intensity) on two distinct functional outcomes: the 40-meter Walk Test and the 30-second Chair Stand Test in patients with KOA.

Methods: A cross-sectional study was conducted with 39 patients diagnosed with clinically and radiographically confirmed KOA (Age: 59.00±7.48 years, 34 females, Body mass index: 31.5 ±4.8 kg/m ² ). Ultrasonographic assessment was performed to measure muscle thickness and muscle quality (via echo intensity) of the quadriceps [Rectus Femoris (RF), Vastus Medialis (VM), Vastus Lateralis (VL), Vastus Intermedius (VI)] and hamstrings [Biceps Femoris (BF) and Semitendinosus (ST)]. Maximal concentric strength of the quadriceps and hamstrings was measured using an isokinetic dynamometer. Functional capacity was evaluated using the 40-meter Walk Test (seconds) and the 30-second Chair Stand Test (number of repetitions). All strength and muscle thickness measurements were normalized to body mass, and all echo-intensity measures were corrected for subcutaneous fat thickness. Pearson’s correlation analysis, followed by univariate and stepwise backward multiple linear regression analyses, were used to determine the primary predictors of functional performance.

Results: The KOA population demonstrated a mean performance of 30.17±5.85 seconds on the 40-meter Walk Test and 10.31±2.51 repetitions on the 30-second Chair Stand Test. There was a strong and positive correlation of the 30-second Chair Stand Test performance with knee extension strength (r = 0.608, p < 0.001) and flexion strength (r = 0.576, p < 0.01). Similarly, the 40-meter Walk Test performance showed a significant negative correlation with knee extension strength (r = -0.515, p < 0.001), indicating that higher strength is associated with shorter walking times. No other neuromuscular parameter showed any associations with performance tests. Stepwise regression models confirmed that knee extension capacity was the strongest independent predictor for both functional outcomes, explaining 37.0% of the variance in the 30-second Chair Stand Test (R ² = 0.370, p < 0.001) and 26.5% of the variance in the 40-meter Walk Test (R ² = 0.265, p < 0.001). While both muscle groups showed initial correlations, only knee extension strength emerged as the sole significant predictor of both functional tests, outweighing the contribution of hamstring strength in predicting functional performance.

Conclusions: Knee extension strength is as the primary neuromuscular determinant of functional performance in patients with KOA explaining 37% of the 30-second Chair Stand Test and 26.5% of the 40-meter Walk Test performance. These findings suggest that although knee flexor (e.g. hamstring) strength, muscle morphology and quality are relevant features of the disease, functional recovery is most effectively predicted by maximal quadriceps strength. Consequently, clinical rehabilitation protocols should prioritize peak torque restoration to achieve optimal improvements in daily functional activities.

REFERENCES: [1] Tayfur, B., Charuphongsa, C., Morrissey, D., & Miller, S. C. (2023). Neuromuscular joint function in knee osteoarthritis: a systematic review and meta-analysis. Annals of physical and rehabilitation medicine, 66(2), 101662.

[2] Aily, J. B., de Noronha, M., Ferrari, R. J., & Mattiello, S. M. (2025). Differences in fatty infiltration in thigh muscles and physical function between people with and without knee osteoarthritis and similar body mass index: a cross-sectional study. BMC Musculoskeletal Disorders , 26 (1), 109.

[3] Taniguchi, M., Fukumoto, Y., Yagi, M., Hirono, T., Yamagata, M., Asayama, A.,. & Ichihashi, N. (2023). A higher intramuscular fat in vastus medialis is associated with functional disabilities and symptoms in early stage of knee osteoarthritis: a case–control study. Arthritis Research & Therapy , 25 (1), 61.

Acknowledgments: NIL.

Disclosure of Interests: None declared.