Symptoms of swelling in the arm may be caused by a minor injury to the soft tissues of the arm. This swelling or soreness is usually caused by overexertion. Soft tissues, such as muscles and fascia, become congested after excessive contraction and prolonged continuous tension. It is because the contraction of myofascia requires a lot of energy and oxygen, and the blood supply and oxygen supply of blood vessels is certain, once the activity is excessive, the blood vessels of myofascia will expand passively and take in more blood to meet the demand of the limb. But the congested state, first of all, increases the pressure inside the soft tissue, causing localized swelling of the arm. A minor injury caused by local overexertion can cause fluid to ooze out of the local soft tissue spaces, further increasing the pressure inside the arm and causing significant swelling symptoms.