The scapula plays a crucial role in proper shoulder function, contributing to synchronized scapular rotation during humeral motion, serving as a stable base for rotator cuff activation, and acting as a key link in the kinetic chain. Each of these functions is essential for optimal arm movement and depends on the integrity of the surrounding shoulder anatomy. However, bone and soft tissue damage, as well as muscle weakness and shortening, can alter the scapula's roles, affecting both its resting position and dynamic motion. This altered scapular position and/or motion is referred to as scapular dyskinesia.

Although scapular dyskinesia is commonly observed in shoulder injuries, it is generally considered a nonspecific response to shoulder pain rather than a direct consequence of a specific glenohumeral pathology. Therefore, assessing the presence or absence of scapular dyskinesia is a critical component of clinical evaluation. A comprehensive assessment should include a visual examination of the scapula at rest and during dynamic humeral movements, as well as objective measurements of posture and the performance of scapular corrective maneuvers. These evaluations assist clinicians in determining the extent to which scapular involvement contributes to a given shoulder injury.

The treatment of scapular dyskinesia should begin with optimizing anatomical alignment, followed by restoring dynamic scapular stability through the strengthening of scapular stabilizers using kinetic chain-based rehabilitation protocols. The kinetic chain, as defined by Steindler, is "a combination of successive joints containing complex motor units." It describes the interconnected movement of joints, where adjacent segments interact to form a continuous chain of motion. This biomechanical model emphasizes that dysfunction in any part of the chain can impact movement quality in both upper and lower segments. The scapula is a foundational component within this system, with surrounding muscles playing a crucial role in stabilizing it.

Postural disorders such as kyphosis can lead to scapular deformities, negatively affecting scapular stability. Rehabilitation professionals and researchers increasingly use the Scapular Muscular Endurance Test (SMET) to assess scapular stability. Given that adolescents are at a heightened risk for musculoskeletal injuries, upper extremity assessments like the SKET may contribute significantly to evaluating this population. However, the validity and reliability of the SMET in adolescents have yet to be established.

This study aims to determine the validity and reliability of the SKET in adolescents.

Inclusion Criteria:

• Being between 10-19 years old
• Being willing to participate in the study

Exclusion Criteria:

• Those who have had major surgery or trauma related to the musculoskeletal system, especially the upper extremity and scapular region
• Those with neurological diseases
• Those with rheumatic diseases in the active phase
• Those with systemic diseases (Diabetes, hypothyroidism, infection, malignancy...)

Adolescents between the ages of 10-19 will be included.