###### Abstract  
The purpose of this study was to compare the effects of a complex shoulder exercise program including respiratory training with those of a similar program including thorax-stabilization exercises on muscle activity and posture in individuals exhibiting scapular internal rotation. The subjects of this study were 32 adults with scapular internal rotation. The exercise group performed the complex shoulder exercise program with respiratory training (EG), while the control group performed the complex shoulder exercise program with thorax-stabilization exercises (CG). After 4 weeks of training, the changes in muscle activity and posture were measured. The differences between the two groups were assessed through comparative analysis using an independent \(t\)-test. The paired \(t\)-test revealed significant disparities in craniovertebral angle (CVA) and sagittal shoulder angle (SSA) posture between the measurements before and after the programs (\(p<0.05\)). Additionally, the paired \(t\)-test indicated notable differences in muscle activity of the upper trapezius (UT), middle trapezius (MT), lower trapezius (LT), and Serratus anterior (SA) muscles (\(p<0.05\)). According to the findings, both intervention groups presented significant improvements in cervical and shoulder posture and muscle activity. Consequently, combination of the complex shoulder exercise program with either respiratory training or thorax-stabilization exercises had a favorable impact on posture and muscle activity among individuals exhibiting scapular internal rotation. elecrumyography; thorax-stabilization exercise; sagittal shoulder angle; craniovertebral angle Xin Yan  
than 30 degrees in the frontal plane, accompanied by anterior tilt and abduction of the scapula, as well as posterior flexion of the thoracic spine. Weaknesses may occur in the middle trapezius (MT), lower trapezius (LT), and serratus anterior (SA) [4,6]. At the same time, the MT, LT, and SA muscles, which link the shoulder blades to the chest and control the elevation of the arm, play an important role in stabilizing the scapula [7, 8, 9]. Muscle weakness and inflexibility can alter the role of the scapula, affecting its resting position and/or dynamic motion [2]. When the position of the scapula changes, the electromyography of the shoulder muscles may also change. Many studies have shown that, in patients with rounded shoulders, there is a significant increase in electromyography activity of the upper trapezius (UT) muscle, while activity of the LT muscle decreases [10]. The coordinated activity of the UT and SA muscles plays a crucial role in the movement and stability of the scapula during upper limb movements, supporting scapular retraction towards the chest and rotation in all three degrees of freedom [11]. When muscles such as the SA and LT are less active, it becomes difficult to stabilize the shoulder blades when raising the arms, reducing their control. The anterior tilt and elevation of the scapula result in increased activity of the UT muscle, which can affect the scapular rhythm and lead to secondary acromial impingement syndrome [12]. Exercise therapy is one of the most evidence-based approaches, and it covers a significant proportion of patients with postural abnormalities. Stretching and strengthening exercises, muscle energy techniques, stabilization exercises, myofascal release techniques, and posture-correction exercises have been approved as effective interventions [13, 14, 15]. The UT muscle can compromise the quality of the upward rotation of the scapula during arm elevation, while the LT muscle attaches to the spine of the scapula and plays a critical role in posteriorly tilting the scapula during upward rotation, generating a force coupled with other scapular muscles that helps to maintain the width in the subacromial space [16].