What is everyone talking about when they talk about lactic acid building up in the legs? I always thought lactic acid was what gave you a stomach ache after spicy food .

I was watching a bike race and the commentator kept talking about the lactic acid buildup showing its toll on x biker.

So basically what is it...how does it happen...and how do you control it (if possible)?

Lactic acid is a result of anaerobic muscle contraction. Your body is constantly making lactic acid, but you can only feel it at high intensity anaerobic work because it is not gotten rid of as fast as it's made. It is lactic acid that gives you the burn in hard workouts. Lactic threshold or LT (Also Anaerobic Threshold) is therefore a critical part of cycling workouts. Once you can raise your lactic threshold, (Your LT is a certain heart rate) you can go longer and harder without the punishing burn. This is possibly the most talked about thing on this board, so do a search. (I know next to nothing compared to some people here.)

The muscle require a chemical (ATP). This is produced in three ways. Two are anaerobic (witout oxygen) as soccerismylife mentioned. Cellular respiration is an aerobic proceess for producton of ATP. People who train use the cellular respiration method more effectively. Less lactate (lactic acid) is produced in people who train. Anaerobic fermentation produces ATP by breaking glucose down to lactic acid. The buildup of lactic acid in the muscles causes the muscles to not relax momentarily. This leads to cramping and even fatique. Simply stated, ateletes can consume oxygen more effectively and break down fatty acids instead of glucose. Courtesy of Humen Biology 8th Edition.

Nice call guys but one more thing -lactic acid is used again! Lactic acid plays a critical role in generating energy during exercise. It provides fuels for many tissues, and turns into fuel for the liver production of glucose and glycogen. So don't think that the need to get rid of it is all good -its a way of saying I need more fuel any way I can get it.
Velocity

Here's a good article that dispels much of the misinformation about "lactic acid".

And if Terry's reference isn't enough, here's another: https://www.cyclingnews.com/fitness.p...ctic_frederick

Thank you for all the information.

I think it's more accurate to say that exercising at your LT produces a certain heart rate (+/- several beats per minute, due to a variety of factors). You CAN raise your LT power without a change in LT heart rate.