Think back to when you first learned about lactic acid (now known to exist in the body as lactate). The context was probably not a good one. In fact, it was probably negative because it meant you couldn’t run as fast as you wanted and that you would lose to your siblings in tag.
The fact of the matter is that lactate prevented you from performing as well as you would have liked. Lactate accumulation is without a doubt disadvantageous for the human body and to argue it as advantageous is to simply ignore a fundamental fact of its existence.
Fatigue commonly occurs during intense exercise and can be induced by factors such as oxidative stress, dehydration and lactic acid accumulation in the muscles.1 Lactic acid accumulation in the muscles can cause intracellular pH to decrease by as much as 0.5 pH units. This acidosis stimulates fatigue by slowing down energy metabolism in the human body (1).
Such fatigue is not confined to the muscle that is exercising. Elevated lactic acid in the blood causes declined performance, even when you go from arm to leg exercise (2). Raising blood pH after it has been reduced by lactic acid has been shown to improve performance and this further supports the correlation of lactic acid with declined performance (2). The reason may be due to the disruption of calcium release and reloading of the sarcoplasmic reticulum which may be caused by lactate and H+ ions (2).
The method of lactic acid incubation, which has been used by some to suggest the benefits of lactate, does not accurately model what takes place during exercise. One deficit is that such experiments model a decreased transmembrane pH gradient when in vivo there is an increase in this gradient in skeletal muscle cells. (2)
Lactic acid and fatigue are correlated. Additionally, getting rid of lactic acid (efflux) is associated with greater performance and the ability of the body to perform efflux can be ascertained with training (2). If lactic acid goes hand in hand with fatigue, getting rid of it improves performance, and the body’s ability to efflux can be improved with training, it seems reasonable to conclude that lactic acid is disadvantageous to the body. If it were advantageous then getting rid of it would cause a decline in performance, not an improvement.
A study done on patients with chronic fatigue syndrome (CFS) showed that these individuals presented with an increase in aerobic Gram positive intestinal bacteria (3). What was interesting was that these bacteria produce D- and L-lactic acids from glucose metabolism. D-lactic acid is thus found elevated in the serum and is associated with cognitive dysfunction and neurological impairment (3). While this study is not directly related to exercise, it shows that chronic lactic acid accumulation can result in chronic fatigue syndrome. Lactic acid accumulation is disadvantageous for these individuals and similarly for healthy, exercising individuals.
References
- Halim H.H., Dek M.S.P., Hamid A.A., and Jaafar A.H. (2017). Fatigue onset through oxidative stress, dehydration and lactic acid accumulation and its in vivo study using experimental animals. Journal of Advanced Review on Scientific Research. 35(1):1-12.
- Lamb G.D., Stephenson D.G, Bangsbo J., and Juel C. (2006). Point:Counterpoint: Lactic acid accumulation is an advantage/disadvantage during muscle activity. Journal of Applied Physiology. 100:1410-1414.
- Sheedy J.R., Wettenhall R.E.H., Scanlon D., Gooley P.R., Lewis D.P., McGregor N., Stapleton D.I., Butt H.L., and Meirleir K.L. (2009). Increased D-Lactic Acid Intestinal Bacteria in Patients with Chronic Fatigue Syndrome. In Vivo. 23(4):621-628.
