How and Why Snacktivity Supports Physical Activity Engagement in Adults With Chronic Low Back Pain: A Realist Review

Background: Physical activity is a recommended first‑line treatment for chronic low back pain, yet adherence to structured exercise remains poor due to pain, fear, fatigue, and contextual barriers. Snacktivity™, which promotes brief, frequent bouts of movement embedded in daily routines, has emerged as a potentially feasible alternative. However, it remains unclear how, why, and for whom Snacktivity supports engagement in people living with chronic low back pain. Objective: To develop and refine programme theories explaining how Snacktivity‑type interventions support physical activity engagement and related outcomes in adults with chronic low back pain. Methods: A realist review was conducted following RAMESES standards. Initial programme theories were developed and iteratively refined through synthesis of quantitative, qualitative, and mixed‑methods evidence from Snacktivity and related sedentary‑reduction interventions in low back pain and transferable adult populations. Evidence was analysed to identify context–mechanism–outcome (CMO) configurations. Results: Forty‑two studies contributed evidence to programme theory refinement. Five refined programme theories were supported. Snacktivity appears to enable engagement by lowering perceived burden and threat rather than eliminating fear, generating mastery experiences that enhance self‑efficacy, and reducing symptom interference through brief, distributed activity. Education and coaching components supported meaning‑making by reframing movement as legitimate and achievable, while environmental cues and routines promoted habit formation. Psychosocial outcomes (confidence, mood, vitality) and habit formation were more consistently improved than performance‑based outcomes, and engagement was sustained even when pain or fatigue persisted. Conclusions: Snacktivity functions as a participation‑enabling intervention rather than a traditional exercise prescription. Its effectiveness in chronic low back pain is explained by psychosocial and contextual mechanisms that support psychological safety, mastery, and habit formation. These findings support a shift from dose‑response exercise models toward interventions that prioritise feasibility, meaning, and sustained participation in daily life.