RESUMEN
BACKGROUND: Stretching programs are often used to improve muscle stiffness and thereby posterior shoulder tightness (PST); however, knowledge about their effects on the viscoelastic properties of muscles and performance is limited. OBJECTIVE: The aim of this study was to investigate the effects of a six-week stretching program on the viscoelastic properties of posterior shoulder muscles, shoulder functional performance and range of motion in volleyball players with PST. STUDY DESIGN: A Randomized Controlled Trial. LEVEL OF EVIDENCE: Level II. METHODS: The study was conducted in 34 male (aged 19-26) professional volleyball players with PST. They were randomly assigned to stretching and control groups. A stretching routine (combining sleeper stretch and cross body stretch exercises) was performed in the stretching group for six weeks. Measurements were taken during the first assessment and six weeks after the initiation of stretching for the following: shoulder external/internal rotation range of motion, spike velocity, single arm seated shot-put test, and infraspinatus- posterior deltoid muscle stiffness (by shear wave elastography). RESULTS: While the stretching group had statistically better results regarding increased shoulder internal rotation (p < 0.01), spike velocity (p = 0.02) and seated single arm shot put distance (p < 0.01), stretching did not have any effect on tissue stiffness. CONCLUSIONS: A 6-week program of sleeper stretch, and cross body stretch exercises improved shoulder internal rotation and functional performance. A clinically meaningful change in muscle mechanical properties cannot be detected after a 6-week stretching program.