Knee extensor muscles of active older adults with knee osteoarthritis are smaller and weaker but not more fatigable than healthy older adults: Relevance to physical function.

Objective: While knee extensor (KE) muscle weakness (lower peak torque or power) is common with knee osteoarthritis (KOA), less is known about muscle fatigue (acute decrement in peak torque or power in response to contractile activity) and its impact on mobility in KOA. The aim of this study was to quantify KE muscle weakness, fatigue and mobility in response to a 30-min treadmill walk (30 MTW) in older adults with and without KOA. Method: Eighteen KOA (73±3 yr) and 18 healthy (71±3 yr,) participants completed a standardized 30 MTW to induce KE muscle fatigue and changes in mobility (Short Physical Performance Battery scores, SPPB). Peak torque and power (120°/s and 240°/s) were quantified pre- and post-30 MTW. Muscle size (maximal fatfree cross-sectional area; mCSA, cm2) and fat fraction were quantified using MRI, and specific power was calculated as peak muscle power/mCSA (Nm×cm-2). Habitual physical activity was quantified using accelerometry. Results: Lower KE peak and specific torque and power, SPPB and gait speed in KOA at baseline indicated weaker, smaller, fattier muscles, and compromised mobility compared with healthy adults. Muscle fatigue post-30 MTW was significant but did not differ by group. SPPB scores did not change post-30 MTW in either group. Conclusion: Older adults with and without KOA experienced KE muscle fatigue in response to a 30 MTW. While KOA were weaker and had lower physical function at baseline, muscle fatigue did not exacerbate these deficits, suggesting that interventions for mobility in individuals with KOA should continue to target muscle atrophy and weakness rather than fatigue.