If you've ever been exercising and hit that point where you felt you could not go on, you know about lactic acid. Lactic acid is a product of normal cellular anaerobic respiration. For years, scientists believed that lactic acid was simply a waste product of anaerobic metabolism. However, lactic acid can be used even during aerobic respiration.
Lactic Acid Production
The primary means that your body uses to metabolize nutrients to produce energy is through aerobic respiration. Aerobic respiration utilizes oxygen to facilitate energy production. When you exercise, your breathing rate increases to keep up with the demand for extra oxygen. However, if your breathing rate and blood flow cannot supply enough oxygen to your working muscles, your body turns to anaerobic respiration. This is the production of energy without the use of oxygen. This system works by producing lactic acid to facilitate energy production. Anaerobic respiration can sustain energy for one to three minutes by producing large amounts of lactic acid. When the body turns back to aerobic respiration, there is generally an accumulation of lactic acid.
Lactic Acid and Aerobic Respiration
During the first minutes of exercise, before oxygen has a chance to catch up with the activity, there are large amount of lactic acid released, which builds up. Your body, being the finely tuned machine that it is, has a way of dealing with this abundance of lactate. The mitochondria of your skeletal muscle cells, the place where aerobic energy production occurs, is able to take in extra lactic acid and metabolize and use it for energy production. So, while aerobic respiration does not produce lactic acid for use, it is still able to use it if it has been produced through other means.
Consequences of Lactic Acid Buildup
Lactic acid, is just that, an acid. While the body can deal with some lactic acid, the accumulation of it can cause fatigue and limit your exercise time. If too much lactic acid is released into your bloodstream, it decreases the pH of your blood. In your muscle, an accumulation of lactic acid can inhibit glycolysis, the breakdown of glycogen into glucose, which is the primary fuel for energy.
Adaptations to Exercise
Over time your body can adapt to most anything you make it do. With training, your body is able to better deal with your body's production of lactic acid. The amount of lactic acid produced by your body declines with training. When it is produced, your body is better able to handle the lactic acid and can utilize it so that it does not accumulate in your muscles or bloodstream. In addition, your body becomes better equipped to fatigue at a higher rate of lactic acid accumulation.
- Scientific American.com; Why Does Lactic Acid Build Up in Muscles? And Why Does It Cause Soreness?; January 2006
- "Exercise Physiology"; George A. Brooks, et al.; 2005
- Sport Fitness Advisor.com; Lactic Acid and Blood Lactate; Phil Davies