Knee extensor functional demand in individuals with knee osteoarthritis

Knee extensor (KE) weakness is commonly exhibited in individuals with knee osteoarthritis (KOA) and may contribute to disability due an increased muscle functional demand and resulting compensatory gait strategies during locomotion. Muscle functional demand is defined as the percentage of maximal strength that is used during a task. The study aim was to quantify KE functional demand in KOA, the impact of walking speed and the relationships with the relative joint contribution to total limb work. Fourteen individuals with symptomatic KOA underwent gait analysis at preferred and faster speeds and isokinetic dynamometry for KE maximum voluntary isometric torque. The KE functional demand as well as the relative and peak joint work and powers were calculated. Paired samples t-test was used to compare functional demand and relative work between speeds and Pearson’s correlation was used to assess the relationship between relative work and functional demand values (α = 0.05). The KE functional demand was 36.0 ± 15.7 % for the preferred speed and significantly higher at 49.8 ± 16.1 % for the faster speed, (t(13) = −5.45, p .05). Knee flexion moment was also significantly higher for the faster speed (t(13) = −5.54, p .001). There were significant relationships between fast speed functional demand and relative ankle negative power (r = −0.57) and relative ankle positive work (r = 0.66), (all p .05). The results suggest that as functional demand nears or exceeds 50 % of the muscle capacity individuals with KOA reduce the relative effort at the knee and use an ankle-based compensation strategy to meet task demands.