Lactic acid – the exercise equivalent of the party pooper?

I’m delighted to bring you a guest post from Matt Higgins today! Matt has a 1st class honours degree in Sports Science (Physiology) from the 5* rated Liverpool John Moores university, as well as diplomas in sports nutrition and sports psychology. His first academic journal article is being considered for publication in the Journal of Sports Science. You can read more about him on The Office Diet’s About page.

Most people who have exercised intensely have felt it. Your muscles ache; you may get cramp or even feel like your muscles could light the bonfire on November 5th. “Damn you lactic acid, I wanted to do even more!”

For many, the perception still remains that lactic acid is a ‘waste product’ resulting from intense exercise and that such accumulation acts as one of or even the main cause of exercise fatigue. This view dates back to experiments completed in the 1930s by AV Hill and others, resulting in the belief that lactic acid was only produced where there was no (anoxic) or too little (hypoxic) oxygen available to the muscle due to the intensity of the exercise.

The facts about lactic acid

However, since the 1970s there has been an academic revolution on the theory of lactic acid and its role within exercise. Unfortunately, it appears such knowledge has not disseminated into the wider public audience, something I will now attempt to address.

Before doing so, it is important to quickly outline some science stuff. When lactic acid accumulates in the body the vast majority of it ‘breaks up’ almost immediately into a salt called lactate (La-) and hydrogen ions (H+). Therefore, when exercise scientists try to measure lactic acid in someone (as often happens for professional athletes), they are more than likely measuring lactate. It is for those reasons that the terms lactic acid and lactate are very often (here also) are interchangeable.

Lactate acid as a fuel

So then, if lactate is not a cause of fatigue, what does it do? Firstly, it is important to point out that the body is almost constantly producing and using lactate as a fuel. Yes, you read correctly – a fuel.

George Brooks, an American scientist, is an eminent researcher in this area. His experiments have shown that the brain, kidneys and liver use lactate as a fuel. Furthermore, the heart is an active lactate consumer with one study showing that up to 60% of the fuel used by the heart is lactate. Moreover, it is now widely accepted that a ‘cell to cell’ lactate shuttle exists. In other words, lactate that is produced in one type of muscle fibre is then used by another type of fibre for fuel. Other studies have demonstrated that lactate can actually be converted (by the liver) back in to glucose or glycogen to be reused by other tissues. In that case is lactate the saviour of all our exercise problems? Well, not really but to demonstrate this, we need to talk science again briefly.

What causes fatigue during exercise?

Although lactate is almost constantly produced and used (cleared) within the body, when we exercise intensely (i.e. 85% of maximum and upwards – hence anaerobically), lactate will accumulate in the muscles. Basically, the rate of production outstrips the rate of clearance and a build up occurs. In the 1930s, it was felt that this accumulation was the main cause of fatigue. However, we know now this not to be true but what is happening?

One school of thought was that the hydrogen ions (H+) that were released caused a decrease in pH in the muscle and therefore this acidosis, as opposed to lactate, was the cause of fatigue. To support this, some experiments have shown that Bicarbonate supplementation has helped increase power output in high intensity exercise suggesting it acts as a pH buffer in the muscle.

However, in contrast another study highlighted that the effect of acidosis previously thought to be implicated in fatigue had actually been described when the experiment was carried out at a non-physiological temperature. In other words, when the experiment was repeated at a temperature closer to the temperature of human muscle in exercise, the effect of acidosis was far less.

Confused? If so, you need not worry. Despite the vast amount of research being carried out into the cause of fatigue, scientists are still unable to pinpoint the exact physiological reason for muscle fatigue. Yes, various components are implicated but as yet, the search for this Holy Grail is still a work in progress.

What is now clear, however, is that lactic acid / lactate is not an exercise party pooper. In fact, it is an extremely important metabolic intermediary within the body that has many different functions. In fact, in a 2007 article in the Sports Medicine journal, George Brooks suggests that more research is required into how lactate maybe able to help marathon runners improve their performance. Viva la revolution.