38 Chapter 2 homogeneity of the patients in the validity study, it appears unlikely that including more patients would have yielded different results. Adherence to HBE programs remains a complex and multi-dimensional construct. Although the EXAS appears to be a valid and reliable instrument, it is still inferior to direct observation. The EXAS shares this disadvantage with every measure of adherence, as all current measurement instruments for adherence to HBE recommendations rely on the patient’s memory, perception, and honesty. Despite this limitation, the EXAS is the only instrument incorporating the quality of exercise performance in the assessment of adherence. Additionally, the EXAS score is an interesting theoretical construct that may allow for new ways to study which determinants of an HBE program are most important for the patient. For instance, an important question to answer in future research will be whether the quality of performance of exercises contributes to treatment effects or whether attention should be focused on adherence to frequency and intensity recommendations alone. Although a focus on the quality of performance of exercises could potentially deter patients from exercising at home, the added attention to detail could also improve a patient’s feeling of being supported by their therapist, increase self-efficacy, and increase the perceived importance of exercising at home as part of their treatment leading to increased adherence. In daily practice, primary care physical therapists and other clinicians often rely on their training and experience to tailor treatment to respond to the individual needs of patients with LBP to achieve the best outcomes. Indeed, tailoring interventions to the patient has been found to increase patient outcomes and enhance treatment effects (36). However, for HBE programs, it remains unclear whether the specific exercises selected by the physical therapist, the quality of performance of the exercises by the patient, or the increase in physical activity from doing exercises are responsible for the effects found. The EXAS score allows researchers to investigate whether clinicians should focus on correct performance of exercises, on adherence to frequency and intensity, or on both. Conclusion The EXAS demonstrates acceptable construct validity for the measurement of adherence to HBE programs. Additionally, the EXAS shows excellent intrarater reliability and poor interrater reliability for the quality of performance score and is the first instrument to measure adherence to frequency, intensity, and quality of performance of HBE programs. The EXAS allows researchers and clinicians to better investigate the effects of adherence to HBE programs on the outcomes of interventions and treatments.
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