Background: The serratus anterior (SA) muscle prevents scapular winging (SW) by stabilizing the medial border of the scapula during arm movement. The upper trapezius (UT) and lower trapezius (LT) muscles may compensate for the weak SA muscle in individuals with SW during shoulder flexion. However, there is no study to examine whether compensation by UT and LT occurs in individuals with SW.
Objects: This study compared the muscle activities of UT, LT, and SA as well as the SA/UT activity ratio between individuals with and without SW during shoulder flexion with load.
Methods: This study recruited 27 participants with SW (n = 14) and without SW (n = 13). Electromyography data of the SA, UT, and LT muscles and SA/UT activity ratio were recorded and analyzed during shoulder flexion with 25% load of the maximal shoulder flexion force. Independent t-test was used to compare the UT, LT, and SA muscle activities and SA/UT ratio between the groups with and without SW; statistical significance was set at α of 0.05.
Results: SA activity was significantly lesser in the group with SW than in the group without SW. However, there were no significant differences in the UT and LT activities and SA/UT activity ratio between the two groups.
Conclusion: The SA activity was lesser in the group with SW than in the group without SW with 25% load of the maximal shoulder flexion force, but there was no compensatory muscle activity of the UT and LT observed. Therefore, further studies are warranted to clarify the compensatory strategy of scapular stabilization in individuals with SW during shoulder flexion under other heavy load conditions.

INTRODUCTION
MATERIALS AND METHODS
    1. Participants
    2. Instruments
    3. Procedures
    4. Statistical Analysis
RESULTS
DISCUSSION
CONCLUSIONS
FUNDING
ACKNOWLEDGEMENTS
CONFLICTS OF INTEREST
AUTHOR CONTRIBUTIONS
ORCID
REFERENCES

• Jang-hun Jung(1Department of Physical and Rehabilitation Medicine, Kyung Hee University Medical Center, College of Medicine Kyung Hee University, 3Department of Physical Therapy, The Graduate School, Yonsei University, 4Department of Physical Therapy, Kinetic Ergocise Based on Movement Analysis Laboratory, College of Health Science, Yonsei University)
• Seung-tak Kang(Department of Physical and Rehabilitation Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Department of Physical Therapy, The Graduate School, Yonsei University,)
• Sung-hoon Jung(Department of Physical Therapy, Kinetic Ergocise Based on Movement Analysis Laboratory, College of Health Science, Yonsei University)
• Oh-yun Kwon(Department of Physical Therapy, Kinetic Ergocise Based on Movement Analysis Laboratory, College of Health Science, Yonsei University) Corresponding author