The cross-sectional association of knee extensor muscle steadiness with peak strength and activity limitations in patients with knee osteoarthritis

Abstract

Background: muscle steadiness is a representative of muscle force control. Muscle steadiness of the knee extensors at submaximal force levels is reduced in patients with knee osteoarthritis (OA) and associated with activity limitations. It is unknown whether muscle steadiness at maximum force levels is associated with activity limitations and if muscle steadiness is associated with peak strength. Aim: The aims of this cross-sectional study were to investigate the association of muscle steadiness with peak strength and the association of muscle steadiness and peak strength with activity limitations in patients with knee OA. Method: 154 patients between 50 and 85 years with symptomatic knee OA performed muscle peak strength testing at 60°/seconds on an isokinetic dynamometer. Steadiness and peak strength were represented by the mean fluctuations and peak value of the torque–time curves, respectively. Activity limitations were assessed with the Get Up and Go (GUG) test, the stair-climbing up (SCU) and down (SCD) test and the WOMAC physical function (PF) subscale questionnaire. Correlation analyses was performed to calculate the association of steadiness with peak strength. Multi variable regression analyses were performed to assess the association of steadiness and peak strength with activity limitations adjusting for potential confounders. Results: Higher peak strength was associated with reduced steadiness (r = 0.63 P < .001) Muscle peak strength was significantly associated with the GUG, SCD, SCU and WOMAC PF-score. (B= -.020, -.024, -.032, -.060 P< .001) Reduced steadiness was associated with shorter GUG and SCD time (B -.258 and -.253 P< .05) but not with SCU and WOMAC PF-score (B -.155 and -.933 P> .05). After adjusting for peak strength there was no significant association of steadiness with activity limitations. (B =-.005, .208, .240 P>.05) Conclusion: reduced muscle steadiness (high fluctuations) is associated with higher muscle strength, faster walking and stair descending. If patients reach a higher level of maximum strength during a maximum effort test, the development of fluctuations are more apparent. Clinical relevance: Longitudinal studies are needed on if and how the level of fluctuations during force development affects motor control and performance in physical tasks that require maximum force.