The influence of exercise on clinical pain and pain mechanisms in patients with subacromial pain syndrome

BACKGROUND: Few studies have investigated the underlying mechanisms for unilateral subacromial pain syndrome (SAPS). Therefore, this study examined (1) if 8‐weeks of exercise could modulate clinical pain or temporal summation of pain (TSP), conditioned pain modulation (CPM), and exercise‐induced hypoalgesia (EIH) and (2) if any of these parameters could predict the effect of 8‐weeks of exercise in patients with unilateral SAPS. METHODS: Thirty‐seven patients completed a progressive abduction exercise program every other day for 8‐weeks. Worst shoulder pain in full abduction was rated on a numeric rating scale (NRS). Pain pressure thresholds (PPTs), TSP, CPM, EIH, Shoulder Pain and Disability Index (SPADI), Pain Catastrophizing Scale (PCS), PainDETECT questionnaire (PD‐Q), Pain Self‐Efficacy Questionnaire (PSE‐Q) and Pittsburgh Sleep Quality Index (PSQI) were assessed before and after intervention. RESULTS: The intervention improved worst pain intensity (p < 0.001), increased the CPM (p < 0.001), improved the sleep scores (p < 0.005) and reduced the PainDETECT ratings (p < 0.001). No changes were observed in PPT, TSP, EIH, SPADI, PCS and PSE‐Q (all p > 0.05). In a linear regression, the combination of all baseline parameters predicted 23.2% variance in absolute change in pain after 8 weeks. Applying backwards elimination to the linear regression yielded that baseline pain intensity combined with TSP predicted 33.8% variance. CONCLUSION: This explorative study suggested reduction in pain, improved sleep quality and increased CPM after 8‐weeks of exercise. Furthermore, the results suggests that low pain intensity and high TSP scores (indicative for pain sensitisation) may predict a lack of pain improvement after exercise.