Quadriceps activation failure as a moderator of the relationship between quadriceps strength and physical function in individuals with knee osteoarthritis
Article first published online: 5 FEB 2004
Copyright © 2004 by the American College of Rheumatology
Arthritis Care & Research
Volume 51, Issue 1, pages 40–48, 15 February 2004
How to Cite
Fitzgerald, G. K., Piva, S. R., Irrgang, J. J., Bouzubar, F. and Starz, T. W. (2004), Quadriceps activation failure as a moderator of the relationship between quadriceps strength and physical function in individuals with knee osteoarthritis. Arthritis & Rheumatism, 51: 40–48. doi: 10.1002/art.20084
- Issue published online: 5 FEB 2004
- Article first published online: 5 FEB 2004
- Manuscript Accepted: 27 MAR 2003
- Manuscript Received: 17 MAY 2002
- Western Pennsylvania Chapter of the Arthritis Foundation
- Quadriceps activation;
- Physical function;
- Quadriceps strength
To determine if quadriceps activation failure (QAF) moderates the relationship between quadriceps strength and physical function in individuals with knee osteoarthritis (OA).
Quadriceps strength and QAF were measured in 105 subjects (80 females) with radiographically confirmed knee OA using a burst-superimposition maximum voluntary isometric quadriceps torque test procedure. Subjects performed the Get Up and Go test as a physical performance measure of function and completed the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) as a self-report measure of function. A principal component analysis was performed to combine the Get Up and Go score and the WOMAC subscores into a single function score. Hierarchical regression analysis was performed to examine the ability of 3 models to predict physical function (strength = function; strength + QAF = function; strength + QAF + [strength × QAF] = function). Partial F tests were used to compare differences in R2 values between each model.
Each model independently predicted the principal component score for function. Adding the strength × QAF interaction term with strength to the model resulted in the highest prediction of function. The strength × QAF interaction indicated that subjects with lower levels of quadriceps strength and higher levels of QAF had lower levels of function than those with comparable levels of weakness but low levels of QAF.
The magnitude of QAF serves to moderate the relationship between quadriceps strength and physical function. Physical function may be more severely affected by weakness of the quadriceps muscles in individuals with knee OA who have higher degrees of QAF than those who may have quadriceps weakness, but do not have QAF.