Background/Objectives: In the shoulder region, shear wave elastography (SWE) has been used to obtain data from multiple muscles. However, there is still a lack of evidence regarding normative values for the supraspinatus muscle. The aim of this study is to estimate the range of normative values and to evaluate the relationship between SWE measurements and isometric strength. Methods: A cross-sectional study with 46 healthy subjects was conducted. Data regarding the SWE of supraspinatus muscle at rest and during contraction and isometric elevation strength were collected. Ordinal cumulative probability models were implemented to calculate normative values based on age and sex. Results: There was a significant increase in muscle stiffness from rest to contraction (3.97; 95% CI, 3.52 to 4.43), but there were no differences between males and females. The ordinal regression models showed a relationship between age and SWE at rest (coefficient, 0.08; 95% CI, 0.01 to 0.14), but not during contraction, and there was no significant age–sex interaction. Normative values of the median and 25th and 75th percentiles were provided based on individuals’ age and sex. There was no correlation between SWE measurements and strength values. Conclusions: Normative values for supraspinatus muscle SWE measurements at rest and during contraction were obtained. These data can help clinicians to interpret measurements of their patients with shoulder disorders.

Background/Objectives: In rotator cuff-related shoulder pain (RCRSP) without associated tendon rupture, therapeutic exercise is one of the main treatment strategies; however, the mechanisms through which it exerts its effects remain poorly understood. The aim of this study was to analyze the role of two potential mechanisms of action: increases in muscle strength and changes in the microarchitecture of the supraspinatus muscle. Methods: This prospective study included 39 patients with RCRSP treated with a strengthening exercise program. Muscle strength was assessed using dynamometry, and supraspinatus muscle stiffness was evaluated using shear wave elastography (SWE) at baseline and after 6 months of exercise. These measurements were correlated with clinical and perceived improvement in the patients. Results: Thirty-seven patients completed follow-up. At 6 months, 67.6% of participants reported being much better or fully recovered, 29.7% reported being somewhat better, and only one patient (2.7%) reported worsening. Overall, the increase in muscle strength was small. In participants reporting marked improvement or full recovery, strength gains were slightly greater, but a significant increase in supraspinatus muscle stiffness was observed. In contrast, participants with mild improvement or worsening showed smaller strength gains and no changes in muscle stiffness. Conclusions: Strength gains following strengthening exercises in RCRSP are small and of limited clinical relevance. In contrast, increased supraspinatus muscle stiffness assessed by SWE was observed after the exercise intervention and may reflect exercise-related adaptations; however, its biological meaning should be interpreted with caution.