Lactic Acid - Friend or Foe?

In the past, whenever you hear lactic acid mentioned, it often comes with a negative connotation.

This is a result of most of us learning either at school or through our involvement in sport, that a build up of lactic acid is bad thing, and is the primary cause for us having to slow down during exercise at high intensities.  We have learnt that when lactic acid builds up our bodies can’t clear it and our muscles become fatigued.  We also attribute the soreness of muscles after exercise to the effects of lactic acid.

Are we wrong?

But some recent studies that have come out suggest that our view on lactic acid and the role it plays in muscle fatigue might not be as accurate as once thought.

To understand this further let’s first take a quick look the two of the bodies main energy systems.

Aerobic and Anaerobic energy systems

Both the aerobic and anaerobic energy systems in our body burn carbohydrate in the form of glucose (blood sugar) and glycogen (muscle sugar).  The main difference between the two systems is the presence of oxygen and the end product or waste.

Moderate exercise is mostly aerobic - with oxygen.  It’s clean burning and there is no end product.  But when exercise becomes more intense and the aerobic system can not supply enough oxygen, the anaerobic system - without oxygen, kicks to provide energy and the end product is lactic acid.

How does our body deal with it?

Now it’s not the creation of lactic acid that has come into question in recent studies, but rather how our bodies deal with this build up of lactic acid and the role it plays during exercise.

In May 2007, George A Brooks from the University of California Berkley, gave an interview with the New York Times.  For over 30 years Brooks has been promoting the theory that lactic acid is actually a fuel source for the body during exercise and not just toxic waste.  Brooks and many of his supporters have argued that lactic acid is created when the muscles break down glucose or glycogen during exercise, and this lactic acid is then taken up by the mitochondria in muscle cells to be used as an alternative fuel source during anaerobic exercise.

Through his research, Brooks has found that mitochondria have special transporter proteins to help absorb the lactic acid to be further broken down.

2 Theories Head to Head

Classic Lactic Acid Theory

Classic lactic acid theory suggests that as a carbohydrate is broken down as fuel, the by product is lactic acid in an anaerobic state.  Lactic acid is believed to be a major contributor to muscle fatigue.  This lactic acid is cleared from your blood until you reach a certain intensity when it starts to interfere with muscle contraction and cause fatigue.

According to this theory you become faster or more efficient as lactic acid is reduced in your body during high intensity exercise for the following reasons.

1. Your body becomes more efficient at utilizing fat as an energy source rather than carbohydrate and therefore less lactic acid is produced.

2. Your body becomes more efficient at clearing the lactic acid from your blood

3. More slow twitch muscle fibres are present and they produce less lactic acid than fast twitch fibres.

NEW Lactic Acid Theory

Whilst the new theory still agrees that lactic acid is produced as a byproduct of carbohydrates being burned during anaerobic exercise, it suggests that lactic acid is not actually cleared in the blood, but rather absorbed by the mitochondria in the muscle fibres.

We know that intense training results in increased mitochondrial density and this supports the new theory by showing how the body develops a greater capacity to break down lactic acid.  It also supports studies which show that elite athletes have lower lactic acid levels during intense exercise.

Here’s the problem

In accepting the new theory on lactic acid we create a massive unknown.

If lactic acid is not the cause of muscle fatigue, then what is?

…and the suggested solution

Here is where the research starts to become interesting.

The New York Times recently reported the findings of Dr Andrew Marks from Columbia University who suggests that muscle fatigue is actually a result of calcium leaking from the muscles during exercise.  Calcium is a critical mineral required for all muscle contraction and less calcium means less contraction and more fatigue.

To confirm this Dr Marks’ researchers gave an experimental drug to mice that inhibited the leaking of calcium from the muscles during exercise.  As a result, the mice were able to run 10-20% longer when using the drug.

This is quite a significant increase in muscle performance and although the drug is currently too dangerous for human consumption, if it were to ever be produced for human use, it would almost instantly be banned due to it’s performance enhancing qualities.

Brooks’ researchers then went on to work with researchers from Appalachian State University where they gathered two groups of trained cyclists.  One group were given the task of riding hard for 3 days in a row, whilst the other group were made to sit in a room for 3 days and do no activity.

Muscle samples were then taken from both groups of trained cyclists and sent back to Columbia University for analysis where they found that calcium had in fact leaked in the samples from the cyclists who rode hard.

But wait there’s more…

Whilst this study suggested an alternative cause of muscle fatigue, the question of lactic acid in it’s role of muscle soreness was still unanswered.  It is believed that lactic acid contributes to DOMS (Delayed Onset Muscle Soreness) which generally peaks 1 or 2 days after the conclusion of exercise.  Many studies have shown that DOMS occurs as a result of eccentric contractions of the muscle (the muscle contracting as it lengthens) as opposed to concentric contractions (muscle shortening whilst contracting).

To investigate this a study was done on a group of runners who were asked to go for two 45 minute runs on separate days.  The first run was done on a flat surface, and the second run was done on a surface with 10% decline.  Blood lactate levels were taken during and after both runs.

The amount of lactate present was actually higher during the level run, however the runners reported little or no muscle soreness from this session.  The amount of lactate was therefore lower during the downhill run and surprisingly the runners reported high occurrence of DOMS after this session - a result of downhill running requiring more eccentric muscle contraction.

In conclusion

So in conclusion it’s becoming more and more common for studies to support the new way of thinking surrounding the effect that lactic acid and calcium have on muscle fatigue.  With this trend continuing in shouldn’t be too long before sports scientists and coaches start to move away from lactic threshold tests with their athletes and we begin to hear more about calcium threshold tests to understand points of fatigue.