Effects of eccentric exercise in patients with subacromial impingement syndrome: a systematic review and meta-analysis

BACKGROUND: Subacromial impingement syndrome is a common problem in primary healthcare. It often include tendinopathy. While exercise therapy is effective for this condition, it is not clear which type of exercise is the most effective. Eccentric exercises has proven effective for treating similar tendinopathies in the lower extremities. The aim of this systematic review was therefore to investigate the effects of eccentric exercise on pain and function in patients with subacromial impingement syndrome compared with other exercise regimens or interventions. A secondary aim was to describe the included components of the various eccentric exercise regimens that have been studied. METHODS: Systematic searches of PubMed, Cochrane Library and PEDro by two independent authors. Included studies were assessed using the PEDro scale for quality and the Cochrane scale for clinical relevance by two independent authors. Data were combined in meta-analyses. GRADE was applied to assess the certainty of evidence. RESULTS: Sixty-eight records were identified. Seven studies (eight articles) were included, six were meta-analysed (n = 281). Included studies were of moderate quality (median PEDro score 7, range 5–8). Post-treatment pain was significantly lower after eccentric exercise compared with other exercise: MD -12.3 (95% CI − 17.8 to − 6.8, I(2) = 7%, p < 0.001), but this difference was not clinically important. Eccentric exercise provided no significant post-treatment improvement in function compared with other exercise: SMD -0.10 (95% CI − 0.79 to 0.58, I(2) = 85%, p = 0.76). Painful eccentric exercise showed no significant difference compared to pain-free eccentric exercise. Eccentric training regimes showed both similarities and diversity. Intervention duration of 6–8 weeks was almost as effective as 12 weeks. CONCLUSIONS: Evidence of low certainty suggests that eccentric exercise may provide a small but likely not clinically important reduction in pain compared with other types of exercise in patients with subacromial impingement syndrome. It is uncertain whether eccentric exercise improves function more than other types of exercise (very low certainty of evidence). Methodological limitations of existing studies make these findings susceptible to change in the future. TRIAL REGISTRATION: PROSPERO CRD42019126917, date of registration: 29-03-2019.