Background: The serratus anterior (SA) is a muscle that performs protraction of the scapulothoracic joint and plays a role in stabilizing the scapula. Imbalances or weaknesses in SA activation are associated with a variety of shoulder dysfunctions, making selective SA strengthening important for rehabilitation. Objects: We aimed to compare the muscle activation of the pectoralis major (PM), SA, external oblique (EO), and internal oblique (IO) during the push-up plus (PUP) exercise with isometric hip adduction (HA) and abdominal drawing-in maneuver (ADIM). Methods: Nineteen healthy male participants performed three PUP exercises: standard PUP, PUP with ADIM, and PUP with HA. Surface electromyography was used to measure and analyze the muscle activity for PM, SA, EO, and IO. Results: PUP with HA showed the lowest PM activity and highest SA activity, and no significant difference was observed between PUP and PUP with ADIM. PUP with ADIM showed significantly the highest EO and IO activity, followed by PUP with HA and PUP. Additionally, PUP with HA showed the lowest PM/SA ratio, and no significant difference was noted between PUP and PUP with ADIM. Conclusion: PUP with HA was able to show high SA muscle activity while reducing PM muscle activity. In addition, PUP with HA can lead to higher EO and IO muscle activity than standard PUP. This exercise could be used as a practical exercise method to selectively strengthen SA and improve scapular muscle stability during early shoulder rehabilitation.

INTRODUCTION
MATERIALS AND METHODS
    1. Participants
    2. Instruments
    3. Procedures
    4. Data Collection
    5. Statistical Analysis
RESULTS
    1. Pectoralis Major
    2. Serratus Anterior
    3. External Oblique
    4. Internal Oblique
    5. Pectoralis Major/Serratus Anterior Activity Ratio
DISCUSSION
CONCLUSIONS
REFERENCES

• Sang-hyuk Lee(Korea Workers' Compensation and Welfare Service Daejeon hospital, Daejeon)
• Jun-hee Kim(Department of Physical Therapy, College of Software and Digital Healthcare Convergence, Yonsei University, Wonju, Korea)
• Oh-yun Kwon(Department of Physical Therapy, College of Software and Digital Healthcare Convergence, Yonsei University, Wonju, Korea) Corresponding author