Liquigas' Vincenzo Nibali is out of gas after finishing second to Frank Schleck in Stage 8 of the 2009 Amgen Tour of California.
Photo: Jesse Hammond/ Active.com
We have all experienced the severe leg pain that comes at the end of a hard jam, a fast climb, or an all-out sprint. This pain is caused by a nemesis of the hard-working cyclist: lactic acid build-up in the muscles.
Just What Is Lactic Acid?
Lactic acid is the end product of anaerobic metabolism, which occurs when there is insufficient oxygen to produce the energy (ATP) required by exercise.
Glycogen stored in the muscle cells is the sole fuel used for anaerobic work. It breaks down to glucose, then pyruvate, and finally to lactic acid when there is not enough oxygen present to the muscle cells.
When that's as far as the process can go because of a lack of oxygen, the result is muscular pain. On the other hand, a sufficient supply of oxygen will allow some lactic acid to be burned and some to be converted back to glycogen. This is the relatively pain-free process of aerobic metabolism.
So, a major factor in lactic acid buildup is the exercise intensity. At about 75 to 85 percent of a cyclist's aerobic capacity, lactic acid production begins increasing in direct proportion to work. When a very high or maximum level of work is reached, lactic acid production becomes constant.
Why it Hurts
At high lactic acid levels, muscular contraction is inhibited. This happens because proteins in muscle cells can function only within a certain range of acidity. Excess lactic acid simply shuts down cellular reactions. The result is acute muscle fatigue. Either the exercise must be stopped or its intensity greatly reduced.
During exercise and for a time afterward, lactic acid escapes from muscles into the blood. Amounts as high as 20 times the resting level have been found after extreme anaerobic work. The exact fate of this excess is not entirely understood.
We do know that the liver is involved with its removal of some lactic acid from the blood. The liver transforms lactic acid into glucose, which is either stored as glycogen or sent out as blood sugar. Through another complicated process, lactic acid is used for fuel by certain heart and muscle cells.
Always keep pedaling after a hard effort. Lactic acid is more rapidly removed from the muscles and resynthesized by light exercise than by rest.
Can Training Make Your Muscles Produce Less Lactic Acid and Tolerate it Better?
It appears so. When your aerobic capacity is increased with training, you produce less lactic acid than you do when untrained. The reason: your aerobic system can better handle lactic acid's precursor, pyruvate.
You are also better able to burn fat for fuel, a process that does not directly produce lactic acid. During maximum efforts, you will also be able to withstand higher lactic acid levels in the muscle, before they begin to fatigue.