FACT: It’s made in different ways.
When you’re spinning along comfortably, your body primarily gets energy via a slow but steady process that converts fat to fuel. But when you put the hammer down, muscles need fuel faster, so they use a speedier process that taps stored carbs, or glycogen. (Load up on these 10 Best Superfoods for Endurance Athletes) Both methods produce lactic acid, which helps supply energy to muscles. The more carbs the body uses, the more lactate accumulates in the muscles and blood.
Video: Bicycle Moves for Abs
FICTION: You can blame it for the burn.
Lactic acid is not what makes your legs threaten mutiny when you’re climbing or going hard (try these Workouts That Help You Crush Every Climb to get better). If anything, it delays the point at which you fatigue by providing fast energy when you’re pushing into the red. The burn you feel when you hit your limit is probably the result of your nervous system sensing increased acidity from the accumulated lactate, Gladden says. (Push through plateaus- 11 Quick Solutions to Cycling Problems.)
FICTION: It causes postride soreness.
In fact, when you ease the pace, the rate at which your body pumps out lactate slows. It doesn’t pool in your legs and make them hurt. Next-day soreness is more likely the result of damage to muscle and connective tissue, or plain old inflammation. Instead, speed up the healing process with these Top Foods for Post-Workout Recovery.
“The better you are at using lactate for energy,” says Gladden, “the better your exercise endurance.” You can teach your body to use lactate more efficiently by putting in lots of miles. But upping your intensity will do the trick in less time. Structure your rides so you spend 10 to 20 percent of the time going hard, at an exertion level of 70 to 80 percent (or higher) of your all-out effort.
It's the point during exercise at which your body is producing lactate faster than your muscles can use it (Learn how to Find Your Lactate Threshold.)