The common causes of arm pain from overexertion are lactic acid accumulation, muscle strain, rotator cuff injury, etc. According to the different causes of the disease, the treatment is also different, and the treatment includes proper rest, medication, surgery and so on. 1. Lactic acid accumulation: After long time physical labor, lactic acid accumulates in the muscles, resulting in arm pain and difficulty in movement, you can take proper rest, reduce activities, or use hot water bags to apply hot compresses locally to improve blood circulation and accelerate lactic acid metabolism. 2. Muscle strain: over-exertion of the arm may lead to muscle strain, pain, swelling, subcutaneous hemorrhage and other symptoms, you can take appropriate rest, use ice to apply cold compresses, oral diclofenac sodium extended-release tablets and other non-steroidal anti-inflammatory drugs to relieve pain. 3. Rotator cuff injury: excessive arm exertion may lead to shoulder joint tendon injury, aseptic inflammation or even ligament rupture, manifested as shoulder joint pain, weakness, difficulty in movement, etc., you can take proper rest, oral diclofenac sodium extended-release tablets and other non-steroidal anti-inflammatory drugs for pain relief, if you consider the tendon rupture, you need to complete the magnetic resonance examination, surgical treatment. If the symptoms of arm pain persist without relief, it is recommended to consult a doctor in time, improve the relevant examination and treatment under the guidance of the doctor.