The right side of the chest pain after running, consider the following 2 reasons: 1. Acute injury to the chest muscles caused by swinging the arm during running, there are pectoralis major and pectoralis minor muscles distributed in front and side of the chest. The repeated swinging of the arm, which constantly pulls and stimulates the pectoralis major and pectoralis minor muscles, may lead to acute muscle damage, which is relatively minor and will be relieved after rest. 2. The repeated activity of the chest muscles during the swinging of the arm causes lactic acid to accumulate. If the lactic acid accumulation is too much and cannot be eliminated in time, the right side of the chest pain will also appear, which can be relieved by giving hot compresses in the treatment.