Sore arms at night may be caused by lactic acid accumulation, muscle strain, cervical spondylosis, etc., and you should consult a doctor in time to find out the cause. 1. Lactic acid accumulation: If you exercise too much or work too hard during the day, the lactic acid produced in the body can not be broken down in a short period of time, and more and more accumulated, and then at night when you go to bed with the symptoms of arm pain, which is a normal physiological phenomenon. 2. Muscle strain: refers to the injury caused by excessive pulling or sharp contraction in sports, which can lead to arm pain and muscle swelling at night when the patient sleeps. 3. Cervical spondylosis: it is caused by cervical degeneration or overwork, when cervical spondylosis compresses the nerve root, it will lead to the symptom that the patient’s arm is sore while sleeping. There may be other reasons for sore arms at night, so you should consult a doctor in time to clarify the specific cause and get appropriate treatment if necessary.