The main causes of pain in the back of the arm are considered to be related to muscle soft tissue strain, inflammation, trauma or overwork. 1. Muscle soft tissue strains: usually in the process of exercise, if excessive force leads to muscle soft tissue strains at the back of the arm, it is easy to directly trigger the symptoms of local pain, the pain will be more pronounced in the process of exercise. 2. Inflammation: usually if excessive force or prolonged weight-bearing strain, may trigger local soft tissue aseptic inflammation, such as fasciitis, etc., if it occurs in the position of the back of the arm, can lead to local pain. 3. Trauma: the position of the back of the arm, if the impact of external forces lead to local injury, it is easy to directly trigger pain, and even accompanied by swelling. 4. Overexertion: Keeping a posture for a long time or over-exertion, frequent muscle contraction is easy to produce fatigue, so the back of the arm pain performance. If the pain in the back of the arm lasts for a longer period of time, you need to check and evaluate the specific cause of the disease, and under the guidance of a professional physician, targeted treatment to prevent the worsening of symptoms in the later stages.