The Limiting Factor

I have recently attended the latest SASMA Conference (South African Sports Medicine Association) which was held at the Wild Coast Sun. Three major, on- going debates in the world of sports medicine were highlighted.

  1. What is the main limiting factor when it comes to exercise?
  2. Which is better ?– Motion control shoes or free movement shoes?
  3. Are carbohydrates good or bad in the diet?

Dr Ross Tucker who is a leading sports Scientist from UCT Institute for Sports medicine presented the heated debate in regards to these topics.  In attendance was Professor Peter Brukner most probably one of the world’s leading sports physicians.

This article will briefly review and discuss the first topic, with the remaining two to be covered in the following months.

So what is the main limiting factor when it comes to exercise?

limiting-factorThere are 2 schools of thought here. One is the peripheral theory. This theory formulates that the muscles ability to convert the body’s energy source from ATP to ADP is limited by a number of factors.  The key ones being that the heart cannot pump the blood around the body fast enough in order to ensure enough oxygen reaches the muscle in time.  The other limiting factor might be the lungs cannot oxygenate the blood fast enough. A 3rd factor might be the VO2 max or the body’s ability to use oxygen more efficiently.  In all these cases the muscles start running out of oxygen and then become anaerobic and produce lactic acid.

Lactic acid is bad right?

No! Lactic acid can convert ADP back to ATP but this can only be done at a certain rate. This means that the body is actually still functioning optimally or aerobically. Lactic acid only becomes a problem when the rate of production of lactic acid and the rate of clearance is out of balance and we start producing more lactic acid than we can use. So is lactic acid clearance rate a possible limiting factor?

Let’s  wait and see!

The 2nd school of thought is what is known as the central governor theory. This theory was formulated by Prof Tim Noakes. He is of the opinion that the brain is the main limiting factor. He demonstrated this by looking at the body’s response when it was aware that exercise was about to happen but hadn’t actually started. An example was looking at people as they were about to walk up stairs. He found that  heart rate suddenly jumped by 20 beats a minute before any exercise was even attempted.  A study conducted on rats where they were injected with barbiturates which knocked out their pain receptors allowed the researchers to run the rats untill they collapsed. This made them look at whether pain is a limiting factor. This also brought to light how fast do we know how to run? Do we run a marathon at the same speed as a 100 m. No, we don’t because the brain programs the body what speed to run at. When we get tired the brain tells the body to slow down.

So what did those clever researchers find?

If 2 athletes with the exact same physiological makeup were competing, the athlete who could handle more pain would win. So this meant that the ability to handle pain was the limiting factor?

Kind of………

The current concept is actually fairly boring. There is no black or white when it comes to limiting factors. Certain individuals can clear lactic acid faster than others. Some can increase the rate of delivery of oxygenated blood to the muscle faster than others. Certain individuals can handle pain better than others.

The take home message is therefore the harder you train, the better each system will become and the less pain you will endure. The better you can handle pain, the harder you can push yourself.  So therefore when you train learn how to push yourself into the pain.

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David Milner - M. Phil (Physio) UCT

David qualified at Wits in 1998 in Physiotherapy. He then went on to also complete his BSc in Physiology in 1999. He started working at Hacks Back sports rehabilitation Practise where he was for 2 years and also joined Kaizer Chiefs soccer in 1999. He has completed his MPhil in Sports Physiotherapy at the University of Cape Town and is currently on the Medical committee of the Professional Soccer League

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