Background Blood flow restriction training (BFRT) has emerged as a promising way to enhance strength and build muscle with low-load exercises. This study was aimed to evaluate the effects of upper limb BFRT on shoulder strength. Methods The literature search encompassed PubMed, Scopus, Ovid, Web of Science, EBSCO, CENTRAL, PEDro, and Google Scholar, with no language restrictions. Included studies were clinical trials investigating the application of BFRT on the upper extremity, specifically assessing shoulder strength in flexion, abduction, internal rotation, and external rotation. The certainty of the evidence was assessed using the GRADE approach. Results Five studies with 158 subjects were included. The pooled analysis revealed a large effect of BFRT on enhancing flexion strength compared to the control group (Morris` dppc = 1.79, 95% CI: 1.09 to 2.49), and moderate to high effect on internal rotation strength (Morris` dppc = 0.67, 95% CI: 0.24 to 1.01). BFRT did not lead to a statistically significant enhancement in abduction and external rotation strength. Conclusion This systematic review and meta-analysis suggests that BFRT has the potential to improve shoulder flexion and internal rotation strength. However, its effects on abduction and external rotation appear to be limited. While the results are encouraging, low to very low certainty of the evidence (as assessed by GRADE) indicates that more high-quality trials are needed to confirm these results.
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