Throughout your sporting and exercising life, the build-up of lactic acid is something that we are indoctrinated to believe is bad for us. The term ‘acid’ alone is enough to raise suspicion, but the truth is that there is far more to this vital metabolite than many care to understand.
A bit of background…
Lactic acid is synonymous to exercise, you hear kids as young as 10 years old saying things like ‘I can’t run anymore, lactic acid is burning’, no doubt because they’ve heard their parents saying it. Well, when it comes to this key energy metabolite and the ‘burn’ that so many complain of, it may not be lactic acid that is solely to blame for this. One of the main causes of the burn you feel in your legs when running, or in your biceps when curling etc, is a change in blood pH. This means that your blood is becoming more acidic due to a cascade of events, starting with a lack of oxygen, or more specifically the failure to remove carbon dioxide. The role of lactic acid (yes lactic acid actually has a function) comes in shortly after this.
Role in energy production
Contrary to common belief, lactic acid has a very real function in the human body, especially during exercise when you’re beginning to tire. As mentioned above, lactic acid is a vital emergency source of energy, when we exercise our bodies predominantly use carbohydrate alongside fat for energy, but when these become exhausted other energy sources come into play. Fat is most effective as an energy source when in the presence of oxygen, so as oxygen becomes less and less the body is restricted to mainly carbohydrate and sometimes protein (glycolytic amino acids). As oxygen becomes less available, carbohydrate becomes more dominant as an energy source via a process called anaerobic glycolysis (without oxygen). Anaerobic glycolysis results in the production of pyruvate, and throughout this stage various metabolites are produced that feed into a cycle called the Krebs cycle to produce energy. However, a by- product of this energy yielding process is lactate and acid in the form of hydrogen ions…and this combo increases acidity.
Hydrogen ions are responsible for the drop in pH that occurs when the body produces energy without oxygen, this means that the bloods acidity increases within the muscle. If exercise continues at an intensity that doesn’t allow the removal of hydrogen ions then the persistent increase in acidity becomes problematic…UNLESS of course you train your muscles to use lactic acid as an energy source!
Using Lactic acid for energy
That is actually lactic acids main function, to be used by the mitochondria for energy. Lactic acid is actually the link between oxidative and glycolytic metabolism, meaning it is integral to the seamless shift from one energy pathway to another during exercise. Basically, the muscle uses carbohydrate for energy, but once this carbohydrate is used up, lactate is formed as a by- product. This lactic acid by- product is then burned to produce even more energy...problem is, the less fit you are, the less sustainable this energy is. The lactic acid that accumulates in the muscle is channelled into the mitochondria (the energy powerhouses) where it is then used to produce energy.
A chap called Ray Peat gave one of the best explanations of oxidative metabolism, and the role of lactic acid I’ve heard:
“If the oxidative metabolism of a cell is compared to a flame, lactic acid is the smoke that’s produced when there isn’t enough oxygen, or when the temperature is too low. Both a cell and a flame produce carbon dioxide when nothing interferes with their oxidation.”
So lactic acid really isn’t the villain it’s made out to be, in fact, it’s a pretty darn integral energy source for exercise. The beauty is, the fitter you get the better you get at using it.
University of California - Berkeley. "Lactic Acid Not Athlete's Poison, But An Energy Source -- If You Know How To Use It." ScienceDaily. ScienceDaily, 21 April 2006. www.sciencedaily.com/releases/2006/04/060420235214.htm