The symptom of tightness on the left side and looseness on the right side of the calf may be caused by different intensity of exercise, unilateral muscle injury, lumbar disc herniation and other factors. 1. Exercise of different intensity: In normal exercise, if the left and right sides of the calf exercise intensity is different, it will lead to different muscle hypertrophy on both sides, thus making the left side of the calf tight and the right side loose. 2. Unilateral muscle injury: strenuous exercise or exercise before the lack of adequate preparatory activities will lead to unilateral muscle tissue injury, resulting in aseptic inflammation, resulting in both sides of the calf belly muscles on one side of the tension on the other side of the flaccid symptoms. 3. Lumbar disc herniation: due to stooping activities or incorrect posture, can lead to degenerative changes in the lumbar spine, and compression of the surrounding nerves, so that the innervated area of dysfunction, resulting in the calf belly on one side of the tightness of one side of the looseness of the situation. As there are many reasons that cause the left side of the calf belly to be tight and the right side to be loose, it is therefore recommended to go to the hospital in time for diagnosis.