The most common causes of muscle soreness in the legs are the following three: 1. It may be caused by lactic acid accumulation in the muscles after strenuous exercise of the lower extremities the day before, which leads to muscle soreness due to lactic acid stimulation. 2. 3, there may be some lumbar spine diseases, such as lumbar spinal stenosis, lumbar spinal slippage or lumbar disc herniation, which compresses the nerve roots of the lower limbs and can lead to soreness, pulling pain, numbness, weakness and other sensations in the leg muscles of the lower limbs.