Scapular dyskinesis (SD) is common in overhead athletes and negatively influence the athletes' performance, increasing the risk of shoulder injury. The kinetic chain (KC) exercises for SD rehabilitation that emphasize importance of core strength and scapula stability during skillful performance. Ai Chi, the aquatic exercises performed in functional positions, which are adequate for power transfer of KC. This study will investigate the effect of KC-based water exercises, Ai Chi, on scapular muscles in overhead athletes with SD.

The purpose of this study is to investigate muscle activations of the upper trapezius (UT), lower trapezius (LT), serratus anterior (SA), latissimus dorsi (LD), and muscle balance ratios of UT/LT, UT/SA I in overhead athletes with SD via KC-based exercise in water and on land. KC-based exercises including the movement patterns of Ai Chi which consist of shoulder flexion/ extension, horizontal abduction/ adduction, internal and external rotation, scapular protraction/retraction combined with spinal rotation.

Inclusion Criteria:

• The participants are overhead athletes with scapular dyskinesis (SD) who played overhead sports activities at least 3 hours/week.

Exclusion Criteria:

• the individuals who have shoulder/neck pain in recent 3 months (VAS >7/10)
• severe shoulder trauma (the collision shoulder, shoulder sprains or strains)
• severe scoliosis (Cobb angle > 25 degrees)
• surgery of upper extremity (the shoulder, cervical spine and elbow) or cervical spine
• peripheral nerve injury or neurological disease (impaired sensation or motor function: numbness, tingle, muscle weakness)
• body mass index (BMI) >25
• infectious disease (upper respiratory tract infection, skin infection, etc.)

The participants are overhead athletes with scapular dyskinesis (SD) who played overhead sports activities at least 3 hours/week.