Running pain in the lateral calf muscles is considered to be caused by lactic acid accumulation, muscle strain, muscle spasm, lumbar disc herniation and other factors. 1. Lactic acid accumulation: after a long period of inactivity, sudden exercise will cause the lateral calf muscles to produce a large amount of lactic acid, which accumulates in the body, thus triggering pain, soreness and other discomforts. 2. Muscle strain: When running, sharp muscle contraction or excessive pulling can cause muscle strain, resulting in pain, redness and swelling of the lateral calf muscles, and there can be obvious pressure pain. 3. Muscle spasm: Running will make the outer calf muscle fatigue, which will trigger muscle spasm, resulting in severe pain in the outer calf muscle and restriction of activities. 4. Lumbar disc herniation: some patients suffer from lumbar disc herniation and other underlying diseases, herniation and compression of nerves cause lower leg pain. In addition, there are many other reasons that can cause running calf muscle pain, it is recommended to consult a doctor in time to identify the cause of the disease, and then actively carry out treatment.