Short-Term Mobility Gains and Unmeasured Longer-Term Outcomes: A Systematic Review and Meta-Analysis of Home-Based Posterior Shoulder Stretching for Glenohumeral Internal Rotation Deficit and Posterior Shoulder Tightness in Active Populations

Background/Objectives: Posterior shoulder stretching is widely prescribed for gleno-humeral internal rotation deficit (GIRD) and posterior shoulder tightness (PST), but durability of benefit and adherence to home programmes are poorly reported. This review evaluated the outcomes and adherence of home-based posterior shoulder stretching programmes in active populations, with pre-specified emphasis on outcomes measured beyond the immediate post-intervention period. Methods: Nine electronic sources, including ClinicalTrials.gov, were searched. Eligible studies were controlled interventions of primarily home-based posterior shoulder stretching in adolescents or adults with GIRD and/or PST. Screening and extraction were performed in duplicate. Risk of bias was assessed using RoB 2 and certainty using GRADE. Continuous outcomes were pooled using random-effects models with mean differences or standardised mean differences. Results: Of 1,228 records, 70 full texts were assessed and nine studies (361 randomised participants) were included. Compared with no stretching or usual activity, stretching increased internal rotation by 13.91° (95% CI 2.61–25.22; two studies, 99 participants; I² = 94%; very low certainty) and horizontal adduction (standardised mean difference 1.20, 95% CI 0.77–1.63; two studies, 99 participants; I² = 0%; low certainty). Sleeper and cross-body stretches did not differ (−0.16°, 95% CI −9.83–9.50; two studies, 53 participants). Five studies reported adherence using five different formats. Conclusions: Low- to very-low-certainty evidence suggests that home-based posterior shoulder stretching may improve shoulder mobility over three to eight weeks, without demonstrated superiority of one technique. No included study provided a post-intervention comparison capable of determining whether stretching-related mobility gains were retained; therefore, durability remains uncertain.