Baseline Psychological Factors and Subsequent Exercise Adherence in Individuals with Chronic Low Back Pain

Background/Objectives: The independent associations between baseline psychological factors and subsequent exercise adherence in chronic low back pain remain uncertain. This exploratory secondary analysis examined these associations while accounting for intervention allocation. Methods: Sixty participants from a randomized trial completed an eight-week exercise program with or without the Move Quiz app. Baseline depression, anxiety and stress were assessed using the Depression Anxiety Stress Scales-21 (DASS-21), kinesiophobia using the Tampa Scale for Kinesiophobia (TSK) and catastrophizing using the Pain Catastrophizing Scale (PCS). Adherence was self-reported using the Exercise Adherence Rating Scale (EARS) at Week 8. Analyses included Spearman correlations, simultaneous regression adjusted for allocation, HC3 robust inference, sensitivity analyses and leave-one-out cross-validation (LOOCV). Results: All five baseline scores correlated inversely with EARS (Spearman rs = −0.55 to −0.78; all p < 0.001). In the allocation-adjusted model, TSK remained associated with lower EARS (B = −0.228, HC3 95% confidence interval [CI] −0.323 to −0.133; p < 0.001). The PCS estimate was negative but less certain (B = −0.082, HC3 95% CI −0.167 to 0.003; p = 0.058); DASS-21 subscales showed no clear independent associations. The model including allocation had R2 = 0.807, LOOCV R2 = 0.757 and root mean squared error = 1.75 EARS points. These are internal performance estimates. Conclusions: Kinesiophobia showed the most consistent association with subsequent self-reported adherence. The small sample, self-reported outcome and uncertain catastrophizing and distress findings support cautious interpretation. Statistical associations and internal model performance do not establish causality, clinical utility or accuracy in independently recruited patients.