Lactic acid, which is produced during strenuous exercise, is both maligned and misunderstood. Although it is commonly blamed for the "burn" you feel with exhaustive exercise, it is hydronium molecules — not lactic acid — that cause the pain. Lactic acid is also falsely blamed for the muscle soreness you may feel 24 to 48 hours after a strenuous workout. In reality, lactic acid is designed by your body to help prevent injury to muscles from extreme exertion.
The energy to fuel strenuous exercise comes from the breakdown of ATP, or adenosine triphosphate. Because your body has a limited supply — about 85 g — of ATP, the substance must be resynthesized. Lactic acid helps to do this by playing a role in anaerobic glycosis: the breakdown of carbohydrates without using oxygen. Glycosis forms hydronium molecules and pyruvic acid, which becomes lactate; when there is not enough oxygen available, the buildup of hydronium causes the pH of muscle cells to drop below normal levels of 7.1, causing acidity. When pH drops to 6.5, muscle contraction is impaired and nerve endings in the muscle are stimulated, causing pain and burning. You may also become disoriented and nauseated.
The point at which acidity occurs in your muscles is called the lactic or lactate threshold, also referred to as the anaerobic threshold. Another way of referring to the phenomenon is OBLA, or onset of blood lactate accumulation. Lactate is simply lactic acid that has been further broken down by the body; when it comes to discussing anaerobic threshold, the terms are used interchangeably. Sports coach Brian Mackenzie notes that the normal amount of lactic acid in your blood is about 1 to 2 millimoles per liter of blood, OBLA occurs when levels rise to between 2 and 4 millimoles per liter.
Raising Lactate Threshold
You can raise your lactate threshold with endurance training. Long, steady runs help develop aerobic capacity by causing the body to develop more small blood vessels, which promote efficient oxygen transport to muscles and help the heart and lungs work more efficiently. The increased availability of oxygen helps to delay the lactate threshold. Coach Brian Mackenzie recommends training continuously at about 85 to 90 percent of your maximum heart rate for 20 minutes to help to improve your lactate threshold. You should perform this type of training once a week, starting eight weeks before a major competition.
Lactic Acid Removal
It takes about an hour for your body to remove excess lactic acid. You can accelerate the process by performing an appropriate cool down, which promotes rapid delivery of oxygen to the muscles. Mild aerobic exercise — such as cycling at a relaxed pace — was shown to be effective in lowering lactate levels in athletes who had performed an intense treadmill run, according to the Brian Mac sports and exercise website. In contrast, both passive recovery — such as lying down — and receiving a massage were ineffective at speeding the lowering of lactic acid levels.
Lactic acid does not play a role in delayed onset muscle soreness, or DOMS. This condition actually results from an inflammatory-repair response to muscle cells damaged in the course of strenuous activity, according to a 2006 article in "Scientific American."