Background/Purpose: Muscle strength, the maximal force generating capacity of skeletal muscle, has been widely characterized in patients with knee osteoarthritis. However, skeletal muscle power, defined as the product of dynamic muscular force and the velocity of muscle contraction, declines earlier and more precipitously than muscle strength across the adult life span. In older populations, peak muscle power is also a more robust predictor of functional outcomes compared to muscle strength, particularly when assessed during closed chain testing. Despite its clinical relevance as a potential determinant of disease burden in knee osteoarthritis (OA), no study to date has comprehensively evaluated lower extremity muscle power output in patients with knee OA. The purpose of this investigation was to examine the relationships between lower extremity muscle power and perceived disease severity in a large population of patients with symptomatic knee OA. We hypothesized that, compared to muscle strength, peak muscle power assessed during bilateral leg press exercise would be a more influential determinant of self-reported pain and health-related quality of life within this patient population. 

Methods: We used baseline data collected as part of a 4-year randomized controlled clinical trial in 181 patients (mean age: 60.2 ± 10yrs, BMI: 32.7 ± 10 kg/m², 69% female, 52% Caucasian) who met the American College of Rheumatology criteria for knee OA. Pain was measured using the pain subscale of the Western Ontario and McMaster Osteoarthritis Index (WOMAC) and health-related quality of life was measured using the Medical Outcomes Study Short Form 36 physical component summary and mental component summary. One-repetition maximum (1RM) strength was measured using the bilateral leg press exercise and peak leg press muscle power was measured during 5 repetitions performed as fast as possible with resistance set to 40% of the 1RM (Keiser Pneumatic Leg Press A420, Keiser Corporation, Fresno, CA).

Results: In univariate regression analysis, greater peak muscle power output was significantly and inversely associated with lower WOMAC pain score (r = -0.17, P = 0.02). Peak muscle power was also significantly and positively associated with SF36 physical component summary score (r = 0.15, P = 0.05) but not mental component summary score (r = -0.02, P = 0.8). After adjusting for age, BMI, sex, race and depressive symptoms, peak muscle power was a significant and independent predictor of SF 36 physical component summary score (P = 0.02). Muscle strength was not associated with any measure of disease severity or quality of life (P ≥ 0.07).

Conclusion: Leg press muscle power output is a significant determinant of perceived disease burden in patients with symptomatic knee OA. While the overall magnitude of these relationships are modest, peak muscle power exerts a greater influence on self reported pain and quality of life compared to muscle strength within this patient population. These data suggest that the efficacy of resistance training interventions specifically designed to improve leg extensor muscle power output should be examined in patients with knee OA.

Supported by the National Center for Complimentary and Alternative Medicine (R01 AT005521-01A1)

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/higher-leg-extensor-muscle-power-output-is-associated-with-reduced-pain-and-better-quality-of-life-in-patients-with-symptomatic-knee-osteoarthritis/