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When someone runs too fast, he may, experience throbbing pain in the leg, muscles. This happens because of, anaerobic respiration taking place in the, muscles., , During running, the energy demand from, the muscle cells increases. This is, compensated by anaerobic respiration, and lactic acid is formed in the process., The deposition of lactic acid causes, pain in the leg muscles. The pain, , subsides after taking rest for some time.