25 Development of the Exercise Adherence Scale (EXAS) in patients with low back pain BACKGROUND Low back pain (LBP) is a major health problem affecting an estimated 576,989,000 (95% confidence interval: 518,940,400 to 637,177,900) people globally in 2017 (1). LBP has been the leading cause of disability in patients with musculoskeletal disorders since 1990, and its global prevalence has continued to increase (1). From 2012 to 2014, the total aggregate medical costs for spine-related problems were an estimated 315.4 USD billion in the United States of America alone (2). The impact of LBP on patient functioning and the economic burden on society call for effective treatments (3). Previous research has shown that exercise therapy is effective in reducing pain intensity and disability in patients with LBP and is cost-effective when combined with stratified care based on risk prognosis (4,5). These exercise therapy interventions often require patients to adhere to a homebased exercise (HBE) program. Adherence to an HBE program is defined as the extent to which a person’s exercise behavior corresponds with agreed recommendations by a health-care professional (6). These recommendations pertain to frequency (i.e. number of exercise sessions per day or week); intensity (i.e. number of repetitions per exercise session); and quality of performance of the HBE program. Furthermore, in this study, an HBE program is defined as a specific exercise or set of specific exercises recommended by a health-care professional to be completed at home to improve impairments in body functions (e.g. joint mobility, muscle strength, or joint stability). Although HBE programs have been shown to be effective, adherence in patients with LBP varies from approximately 70% to 90% and declines significantly over time (7,8). Additionally, adherence is difficult to assess due to the high rate of socially desirable answers provided by patients using diaries to record adherence, as well as the lack of a clinimetrically tested, standardized measure of exercise adherence (9–12). As a result, the treatment effects of HBE programs on LBP can be underestimated due to poor adherence rates in both research and clinical practice. To better investigate the effects of patient adherence to HBE programs on treatment outcomes, researchers require a reliable and valid measure of adherence (9,10). Additionally, a reliable and valid measure of adherence will allow clinicians to optimize patient adherence to HBE programs and improve treatment outcomes by tailoring treatments to individual patients. For example, strategies to increase self-efficacy, guidance, or exercise attention can be employed to improve low adherence to HBE programs (13,14). Current measures of adherence to HBE programs employ a variety of strategies to measure adherence behavior (9,10,15). Bollen et al. (2014) found 29 questionnaires, 29 diaries, two visual analog scales, and a tally counter (9). Most of these instruments had been used in only one study and lacked clinimetric testing, emphasizing the absence of a reliable, valid, and standardized means to measure adherence behavior (9). Moreover, the existing 2
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