Lactic acid, or lactate, is produced in muscle cells by the anaerobic breakdown of glycogen during short bursts of high-intensity exercise. It forms when the body metabolizes carbohydrates to generate energy when oxygen levels are low. It may remain in the muscles after strenuous exercise for some time until it the body breaks it down.
Significance
High levels of lactic acid accumulating in the muscles and blood impair performance time of high-intensity exercise. Moreover, the lactic acid remaining after exercise causes muscle pain and fatigue, the remedy of which is often thought to be rest. However, by increasing anaerobic threshold -- the point at which lactic acid begins to accumulate -- through recovery exercise, as opposed to resting, the body actually metabolizes lactic acid faster, thus diminishing post-exercise pain and fatigue.
Study
In a study conducted by Yiannis Koutedaki, et.al., at the University of Birmingham, seven rowers were subjected to three tests after completing a 2,000m race in a rowing boat at maximal exertion. Each test sought to determine the effectiveness of varying intensities of exercise in reducing blood lactic acid. In the first test, lactic acid build up was measured during a 13-minute recovery exercise at 60 percent of maximum rowing speed.
In the second test, subjects were instructed to row at 40 percent of their maximum speed. The third test comprised a resting recovery period. Results indicated the highest rate of lactic acid removal after the 40 percent recovery exercise, thus suggesting that an active recovery of 40 percent of maximum exertion promotes lactic acid removal more effectively that a resting recovery.
Threshold Training
According to Len Kravitz, et. al., of the University of New Mexico, an optimum training program includes a high volume of cardiovascular exercise, 70 percent of which includes moderate intensity exercise, 20 percent is at maximal lactate steady state--highest intensity sustained with steady blood lactate levels -- and 10 percent is dedicated to high-intensity interval training. This combination of exercise produces the greatest effect on lactate threshold improvement.
Considerations
Although an active recovery is more beneficial for improving lactate threshold than a resting recovery, it is vital that you include rest days in your training program. According to fitness website Fitness Friends, the body needs time to adapt and repair itself; neglecting to rest increases the risk of injury. Depending on your fitness level, rest one day after two to three training days, or every other day.
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