I just read the PPRR club newsletter. I am sure many of you are members as well. Regina Hammonds has a very good nutrition quiz. There is one question that bugs me. It is not that she is not correct, but I think it can lead to confusion and misunderstanding. The question (#3) concerns fat burning. She states that around 55% of VO2max is maximal fat burning. Well, what is maximal? It is not the percentage of fat burned because you are burning almost all fat sitting and reading this post. Yep, at rest you get almost all your energy from fat. (Note: while people tend to think of our energy systems as distinct, all energy systems are at work at all times. The predominate one is largely dependent on intensity and duration---and these two are related). The attached slides illustrate with percentages and actual number of kcals expended. While this was done with cyclists (using watts) the principle applies to runners. Please note this data is from an actual test and involves the same athlete. In one slide the data is represented as a % but in the other as absolute kilocalories. Notice that at 80W (very low intensity) the PERCENTAGE of fat burned is high (51%), but if you look at the absolute energy expenditure from fat you will see that about 4 kcals/min. However, look at 250W. The percentage of fat used is lower (41%) but you are expending 6 kcals/min. You are actually burning 50% more fat at the higher intensity. How is this happening? Well at the higher intensity, your overall energy expenditure is higher such that even if the percentage of fat is lower, it is a smaller percentage of a much larger number. So if you are really interested in burning fat, a higher intensity workout can do the job. While you cannot maintain that higher intensity for as long, do not think that you are not burning fat even at what might be a comfortably hard intensity. But you cannot run that hard every day either so you must vary the intensity and duration. Lastly, one aspect of weight loss (and by this I mean fat mass loss) is to create an energy deficit. In short, you do not need to burn fat to lose fat mass. If you know how sprinters train, you know that they either at at very high intensity or doing virtually nothing. They do very little activity in the fat burning range compared to distance runners. But is Usain Bolt or Tyson Gay fat?
Posted on: Sat, 06 Dec 2014 18:51:33 +0000
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