The causes of arm soreness may be lactic acid buildup, soft tissue injury, whiplash, etc., as follows: 1. Lactic acid accumulation: when the arm exercise is too large, from the cell aerobic metabolism to produce energy is not enough to supply, the cell will carry out anaerobic fermentation to produce the ability to produce a large number of intermediate metabolites in the process of anaerobic exercise, such as lactic acid, thus forming lactic acid accumulation. Excessive lactic acid stimulates the muscles, causing arm soreness. 2. Soft Tissue Injury: When there is a sudden intense and large amount of arm activity in the case of inadequate warm-up, it may cause acute injuries such as muscle strains and ligament tears, thus causing soreness and pain in the arms during or after exercise. 3. Cervical spondylosis: when suffering from cervical spondylosis, it can lead to nerve root compression, and a series of uncomfortable symptoms will appear in the corresponding innervated area, in addition to arm soreness and swelling, there can also be pain and sensory loss symptoms. There may also be other reasons for arm pain and swelling, it is recommended to go to the hospital in time, improve the examination to clarify the cause of the disease, under the guidance of the doctor to give targeted treatment or treatment.