There are many reasons for small arm muscle soreness, common causes are excessive exercise, trauma, cervical spondylosis and frozen shoulder. 1. Excessive exercise: when using the upper arm for a long time to carry out physical activities or upper arm fitness excessive exercise, a large number of lactic acid will accumulate in the arm, resulting in physiological arm soreness, generally can be relieved after rest. 2. Trauma: trauma leads to soft tissue damage around the arm, pain, swelling, will also appear in the arm soreness phenomenon. 3. Cervical spondylosis: degeneration and protrusion of cervical intervertebral discs compress the nerve roots innervating the upper limbs, which may cause pain and numbness in the upper limbs, as well as soreness and swelling in the muscles of the lower arms. 4. Frozen shoulder: due to trauma or exertion caused by aseptic inflammation of the soft tissues around the shoulder joint, there can be pain in the shoulder, activity limitation, part of the distal upper extremity can be radiated to the small arm soreness and swelling. There may be other causes of small arm muscle soreness, such as carpal tunnel syndrome, elbow tube syndrome, upper extremity vascular disease, etc. If the rest does not relieve, it is recommended to consult a doctor in a timely manner, improve the relevant examination, clarify the cause of the disease and then comply with the doctor’s instructions for targeted treatment, so as not to delay the condition.