Ultrasound-Based Assessment of Shoulder Soft Tissue Alterations in Young Adults Performing Upper Limb Weight Training: A Cross-Sectional Study

Background: The subacromial space, measured as the acromiohumeral distance (AHD), is a key determinant of shoulder biomechanics and injury risk. Athletes performing repetitive upper-limb resistance training are particularly exposed to cumulative tendon stress. Musculoskeletal ultrasound (US) enables dynamic, cost-effective assessment, yet its role in strength athletes remains underexplored. The aim of this study was to determine whether young adults engaged in regular upper-limb weight training present a narrower acromiohumeral distance and a higher prevalence of ultrasound-detected tendon abnormalities compared with non-weight-training individuals. Methods: We conducted a post hoc subanalysis of a cross-sectional cohort of 66 young adults (18–45 years; mean 29.6 ± 9.0 years; 27 men/39 women) evaluated with standardized shoulder US. Participants were classified as weight-training (n = 15; 36.2 ± 5.7 years; 11 men/4 women) or non-weight-training (n = 51; 27.6 ± 8.8 years; 16 men/35 women). AHD was measured in millimeters, and abnormalities of the supraspinatus, subscapularis, long head of the biceps tendon (LHBT), and subacromial–subdeltoid bursa were recorded. Between-group comparisons used Welch’s t-test or χ2/Fisher’s exact test; effect sizes were expressed as Cohen’s d or odds ratios (OR). Multiple testing was corrected with the false discovery rate (FDR). Results: Weight-training participants exhibited a significantly smaller AHD (7.13 ± 0.54 vs. 7.49 ± 0.68 mm; t (28) = −2.12, p = 0.038; mean difference −0.36 mm, 95% CI −0.70 to −0.03; Cohen’s d = −0.56). Supraspinatus tendinopathy was more prevalent in weight-training athletes (93.3% vs. 41.2%; OR 17.7, 95% CI 2.16–145.8; FDR-adjusted p = 0.003). Subscapularis tendinitis (40.0% vs. 17.6%; OR 3.58, 95% CI 1.00–12.88; FDR p = 0.14) and LHBT tenosynovitis (20.0% vs. 3.9%; OR 6.82, 95% CI 1.02–45.8; FDR p = 0.09) showed non-significant trends. Conclusions: Upper-limb weight training in young adults is associated with reduced AHD and a markedly higher prevalence of supraspinatus tendinopathy. Ultrasound proved valuable for early detection of structural and morphological alterations in shoulder soft tissues. Preventive strategies focusing on load management, exercise technique, and targeted strengthening should be prioritized.