Self-Efficacy, Physical Function and Quality of Life in Individuals With Knee Osteoarthritis
Sadiq, Abdul K. Jafar
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Background and Purpose: Self-efficacy plays a major role in determining physical function during the earlier stages of the knee osteoarthritis (OA) and it may be a significant factor in the maintenance of physical function across the span of OA severity. This study examined the contribution of self-efficacy to objective and subjective measures of physical function at both maximal and sub-maximal levels. The relationship between self-efficacy and quality of life was also examined. Participants: Twenty community-dwelling adults with knee OA (age 69±14 years) were recruited for this study. Methods: Subjective maximal and sub-maximal performance were determined using the Maximal Activity Score (MAS) and Adjusted Activity Score (AAS) respectively of the Human Activity Profile. The objective measure of sub-maximal physical function was the 6-minute walk test (6MWT) while the Incremental Shuttle Walk Test (ISWT) was the maximal measure. Quality of life was determined using the Short Form Health Survey 36 (SF-36) and self-efficacy was measured using the Arthritis Self-Efficacy (ASE) scale. Disease severity was determined using the Western Ontario and McMaster University Osteoarthritis Index (WOMAC). A stepwise multiple linear regression analysis was performed using each of 6MWT, ISWT, AAS and MAS as the dependent variable, and the WOMAC and ASE as independent variables. Results: Self-efficacy explained 44% of the variance in the 6MWT but only 16% in the ISWT. Self-efficacy explained approximately 30% of the variance in both the MAS and AAS. A moderate relationship was observed between self-efficacy and the Physical Component Score (PCS) (r=0.51) of health-related quality of life, but no relationship was observed with the Mental Component Score (MCS). Discussion and Conclusion: In mild to moderate knee OA, sub-maximal physical function was substantively influenced by an individual’s belief in his/her ability to perform a given task, but not so when the intensity of the activity approached maximal levels. This differential relationship between sub-maximal and maximal performance was not present using subjective reports of performance. These findings indicate that therapy utilizing training at sub-maximal levels in mild to moderate knee OA should focus on strategies for enhancing self-efficacy; whereas with training at relatively high intensities, less focus should be given to enhancing self-efficacy.