胸肌發出聲音　\囧/ - 健身

http://tinyurl.com/yavsp8m
隨便幫你google到的，正確性我也不知道，內容有提到Physical strain可能造成
This may be seen in excessive weight lifting (bench pressing)
or other activities that put pressure on the chest wall, its muscles and bones.
A person who supports their body weight on one hand or elbow over long periods
may transfer the weight across the costal cartilage and thereby strain the joint
possibly leading to inflammation or sublaxation.

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