This situation is because muscle contraction urgently needs a lot of energy supply, and the oxygen demand is greatly increased. The oxygen supply of the body cannot meet the energy demand of muscle contraction for the time being. In order to meet the needs of energy, the anaerobic process is strengthened and a large amount of lactic acid is produced. Excessive accumulation of lactic acid in muscle will stimulate chemoreceptors in muscle or make muscle swell due to excessive accumulation, thus making muscle feel sore.
This situation does not need treatment, and will return to normal after adequate rest. Now you can gently rub the sore part of your shoulder. Conducive to relieving pain.