Acute Effects of Focal Vibration on Posterior Shoulder Tightness and Tissue Stiffness in Overhead Athletes

Repetitive overhead sports activities lead to sport-specific adaptations in the glenohumeral joint and the surrounding soft tissues. One of the most common adaptations is posterior shoulder tightness, which has been associated with reduced glenohumeral range of motion, altered scapulohumeral rhythm, impaired shoulder biomechanics, and an increased risk of shoulder injury. In addition, changes in the mechanical properties of the posterior shoulder muscles may adversely affect shoulder function and athletic performance. Therefore, identifying effective, evidence-based interventions to reduce posterior shoulder tightness is of considerable clinical importance.

Focal vibration is a non-invasive therapeutic intervention that stimulates muscle spindles, enhances proprioceptive feedback, improves neuromuscular control, and may alter the mechanical properties of soft tissues. However, evidence regarding the acute effects of focal vibration on posterior shoulder tightness, muscle stiffness, and glenohumeral range of motion in overhead athletes remains limited.

This study is designed as a single-blind, randomized, sham-controlled trial to investigate the acute effects of focal vibration on posterior shoulder tightness, posterior shoulder muscle stiffness, and glenohumeral internal and external rotation range of motion in overhead athletes. Participants will be randomly assigned to either the focal vibration group or the sham control group using block randomization. All assessments will be performed by the same investigator using standardized testing procedures immediately before and immediately after a single intervention session.

Posterior shoulder tightness will be assessed using the Horizontal Adduction Test. The stiffness of the posterior deltoid, infraspinatus, and teres minor muscles will be measured using the IndentoPRO digital tissue indentometer. Passive glenohumeral internal and external rotation range of motion will be assessed using the GYKO inertial sensor. Between-group and within-group differences will be analyzed using appropriate statistical methods.

This study aims to provide evidence regarding the acute effects of focal vibration on posterior shoulder tightness and the mechanical properties of posterior shoulder muscles, thereby contributing to evidence-based clinical practice in sports rehabilitation, performance enhancement, and shoulder injury prevention.

Inclusion criteria

Aged between 18 and 25 years. Regular participation in an overhead sport for at least 4 years. Participating in regular training at least 4 times per week. Willing to participate voluntarily in the study and able to provide written informed consent.

Exclusion criteria

History of shoulder surgery within the previous 6 months. History of shoulder, neck, or upper extremity injury within the previous 3 months.

Participation in intense upper extremity training within the previous 48 hours. Presence of infection, skin lesions, or open wounds around the shoulder region. Diagnosis of a systemic rheumatologic or neurological disease. Unwillingness to participate in the study or refusal to provide written informed consent.