Muscle activation of the upper trapezius, lower trapezius and serratus anterior muscles will be measured during prone scapular retraction exercises. Then the same exercises will be performed with abdominal contraction using a stabilizer and muscle activity of the same muscles will be measured. A comparison will be made between the two conditions.

The scapula plays an important role in providing both movement and stability of the shoulder joint. Correct scapular position and movement is achieved through the synchronized firing of muscles to provide optimal length-tension relationships between the scapular stabilizers. During arm elevation, coordinated muscle activation is seen between the serratus anterior (SA) and trapezius to provide controlled scapular upward rotation. Therefore, analyzing the muscle activation rates of these synergistic pairs (upper trapezius/serratus anterior [UT/SA] or upper trapezius/lower trapezius [UT/LT]) helps us understand scapular muscle function and prescribe exercises. Rehabilitation has focused on LT and SA muscle strengthening exercises to treat shoulder dysfunction . From a mechanical point of view, trunk and pelvis stability is required to transmit force and energy to the upper extremities during function or sports activities.

An altered spinal alignment directly affects the movement of the shoulder and scapular muscles, altering scapular position and stability. Coordinated activity of the shoulder and scapular muscles is essential to increase dynamic stability during shoulder movement; therefore, altered muscle activity can produce inappropriate glenohumeral and scapulothoracic joint movement rhythm and cause various shoulder pathologies examined the effect on the surface electromyographic activity of the scapulothoracic (UT, SA and LT) and middle deltoid muscles during isometric contraction in 45° shoulder abduction in the standing scapular plane supported by a pelvic and thoracic belt and reported that it did not significantly increase SA, LT activation, but increased middle deltoid activation and decreased UT electromyography activity observed an increase in the activity of the serratus anterior muscle during crossed shoulder flexion and scaption exercises with voluntary abdominal muscle contraction.

The resistance provided by isotonic exercise depends on gravity and the resistance pattern varies according to changes in the patient's body position (standing, prone, supine). In the prone position, it is often preferred because the scapular muscles can be strengthened in isolation by eliminating the lower extremity and core muscles. In a study in which trapezius muscle activation was examined by performing scapula retraction exercises in the prone position, a higher increase in trapezius muscle activation was reported compared to the standing study . It has been shown that there is a significantly greater increase in muscle activation in all 3 parts of the trapezius muscle in the prone position compared to the side lying and standing positions. It has been reported that this may be due to the fact that exercises performed prone against gravity may give more load to the trapezius muscle than the standing position. Although lower extremity movements are limited in the prone position compared to the standing position, anterior pelvic tilt formation as a result of excessive lumbar spine movements during exercises performed in this position should not be overlooked.

Therefore, our aim in this study was to investigate scapulothoracic muscle activations during open kinetic chain strengthening exercises with scapular stabilizers by providing lumbopelvic stability with voluntary abdominal contraction in the prone position.

Inclusion Criteria:

• Healthy individuals between the ages of 18-30
• Physical activity level of at least 5 on the Tegner activity scale.

Exclusion Criteria:

• Having pathology of the shoulder and spine
• History of previous upper extremity surgery
• Body mass index greater than 24.9
• Experience with core stability training.

The study will include 30 healthy participants regardless of gender.