This Is a Certified Answer

Certified answers contain reliable, trustworthy information vouched for by a hand-picked team of experts. Brainly has millions of high quality answers, all of them carefully moderated by our most trusted community members, but certified answers are the finest of the finest.
When he starts running anaerobic respiration starts taking place in the muscles and lactic acid is produced and it gets accumulated in it.this is the reason why our legs start paining