Ouch, it burns! But what is "it" \u2014 the root cause of the pain in your legs when you smash it up a hard climb? For the longest time, we colloquially called "it" lactic acid. It turns out that was wrong.\n\nCoach Trevor Connor and Caley Fretz examine the chemistry that occurs in our muscles while riding and racing. They talk to Dr. I\xf1igo San Mill\xe1n, who is the director of Colorado University's exercise physiology lab. Best of all, they give you practical advice for your own training to help make that burn go away \u2014 or at least make you faster even if it hurts.