Background: Push-up are effective exercises for shoulder stability. Previous studies have documented the effects of support plane and hand position and width on muscle activities during a push-up.
Objects: This study aimed to investigate the changes in muscle activities in the upper extremity when performing the standard and the knee-flexed push-up with different hand shapes.
Methods: A total of twenty-six healthy males participated in this study. Three different hand shapes (finger abduction, finger adduction, and fists) and two types of push-up posture (standard and knee-flexed push-up) were set as the independent variables. Electrograms were used to measure the muscle activity of the upper trapezius (UT), triceps brachii (TB), pectoralis major (PM), and serratus anterior (SA). Each participant performed the randomly assigned push-up to the sound of the metronome. The mixed-effect linear regression model was used to detect the changes in muscle activities after changing the hand shape and push-up posture. Statistical significance was set at α = 0.05.
Results: The UT muscle activity was statistically significantly higher when performing push-up with fists than finger abduction (p = 0.035) or finger adduction (p = 0.044). During the standard push-up, the muscle activity in all muscles was that the push-up with fists showed the highest muscle activity compared to the finger abduction (p < 0.01) and finger adduction (p < 0.01). Regardless of the shape of the hand, UT had the lowest muscle activity compared to other muscles (p < 0.001). In contrast, the SA muscle had the highest muscle activity among four muscles during the standard push-up.
Conclusion: Based on the results of this study, we suggest hand shape is related to the difficulty level of push-up either in the standard or the knee-flexed push-up, especially in the push-up with fists. In addition, knee push-up can be recommended as shoulder musclestrengthening exercises for individuals with low shoulder muscle strength.

INTRODUCTION
MATERIALS AND METHODS
    1. 연구 대상
    2. 측정 도구
    3. 실험 방법
    4. 자료 분석
RESULTS
    1. 무릎 팔굽혀펴기 시 손 모양에 따른 어깨 관련 근육 별%MVIC의 차이
    2. 표준 팔굽혀펴기 시 손 모양에 따른 어깨 관련 근육 별%MVIC의 차이
    3. 팔굽혀펴기 자세에 따른 어깨 관련 근육 별 %MVIC의 차이
DISCUSSION
CONCLUSIONS
FUNDING
ACKNOWLEDGEMENTS
CONFLICTS OF INTEREST
AUTHOR CONTRIBUTIONS
ORCID
REFERENCES

• 정상진(전주대학교 물리치료학과) | Sang-jin Jeong (Department of Physical Therapy, Jeonju University, Jeonju, Korea)
• 김지혜(전주대학교 물리치료학과) | Ji-hye Kim (Department of Physical Therapy, Jeonju University, Jeonju, Korea)
• 공해진(전주대학교 물리치료학과) | Hae-jin Kong (Department of Physical Therapy, Jeonju University, Jeonju, Korea)
• 조민지(전주대학교 물리치료학과) | Min-ji Cho (Department of Physical Therapy, Jeonju University, Jeonju, Korea)
• 백현지(전주대학교 물리치료학과) | Hyeon-ji Baek (Department of Physical Therapy, Jeonju University, Jeonju, Korea)
• 김수진(전주대학교 물리치료학과) | Su-jin Kim (Department of Physical Therapy, Jeonju University, Jeonju, Korea) Corresponding author