Background/Purpose In exercise intervention trials, higher outcome expectancy can predict stronger adherence. Such expectancy is known to be associated with gender, age, marital status, physical and mental health, and self-efficacy.  However, it remains unclear whether specific disease conditions may help discriminate high expectancy individuals from those with moderate expectancy when screening participants for clinical trials. This study aimed to explore whether physical and mental health factors are associated with outcome expectations for exercise among patients with knee osteoarthritis (KOA) participating a large clinical trial.

Methods We conducted a secondary analysis of baseline data from a randomized clinical trial comparing physical therapy and Tai Chi among individuals with KOA defined by the American College of Rheumatology criteria. We assessed expectancy for exercise with a 9-item Outcome Expectations for Exercise (OES) questionnaire, which utilizes a 5-point scale where a higher value indicates stronger expectation for a positive outcome. Participants reported the degree of pain and physical function through the WOMAC questionnaire. They also reported their confidence in coping with chronic pain through the Chronic Pain Self-Efficacy Scale (CPSS). A single reader scored radiographs for KL grades. We assessed participants’ mental status with the Beck II scale and PROMIS anxiety inventory.

OES was analyzed as a binary variable (<4 versus ≥4). The physical and psychological parameters were analyzed as tertiles. Separate logistic regression models were performed to evaluate the relationship between OES and each of the physical and psychological parameters, controlled for age, gender, and BMI. Statistical significance was set at p<0.05.

Results The 282 participants in the trial were 69% female; 51% white and 35% African American; aged 59.7±10.4 years (mean ± SD); and 51% with a low KL score (0-2), 22% with a moderate KL score (3), and 27% with a high KL score (4). Table 1 shows the odds ratio of higher OES for the six physical and psychological parameters after adjustment for age, gender, and BMI. We found that Beck II score and self-efficacy were significantly associated with OES.

Conclusion The participants with worse depression symptoms and lower confidence in coping chronic pain tended to have lower outcome expectations. We observed trends that more severe self-reported symptoms and worse radiographic KOA severity were associated with higher outcome expectancy, although the statistical tests failed to reach significance. Such relationship may be confirmed by a larger sample size. Our results showed that in the clinical trials settings, high outcome expectancy populations may be identified through physical and psychological measurements, though further research is needed to determine their predictive ability.

Table 1. Odds ratios for high outcome expectations (OES ≥4) by physical and psychological parameters