While looking up the concept of ‘personal best fitness’, I came across some interesting information about how our bodies get energy for exercise. What I find most interesting is that our bodies use different energy sources depending on how hard we are exercising. If we exercise with a relatively low intensity- up to 50 or 60% of our maximum intensity- we burn fat, but if we exercise at a higher intensity, we burn carbohydrates. This finally explains something which I have never fully understood, that being why it is possible for some people to run for days and days on end, while others experience what is variously referred to as “hitting the wall” or “bonking”- the situtation where you suddenly run out of energy and sometimes literally can go no further. Basically the answer is that if you are exercising at a low intensity, you have a lot of energy available to you, because as humans we have good stores of fat energy (several days worth, according to the article!). However, if you are exercising at high intensity, you have a fairly limited amount of energy available to you- only about two hours worth- since we can’t store very many carbohydrates.
I think this also explains why, when I bike in my usual slow and
somewhat slacker-ish manner, I don’t have any great difficulties biking
for long periods of time. I’m going slowly enough that my muscles can be
well supplied with the oxygen they need, they don’t get overly tired, and
I’m drawing on fat for energy rather than those limited supplies of carbs,
so I can keep going and going and going. This also explains why, when I’m
running, quite the opposite is true. I’m exercising at a much higher
intensity, so before too long both my muscles conk out, and I get hungry
and need to eat something. The advantage to exercising over time is that
your highest level of intensity gets higher, power or performance wise, than it was before, and that
means you can exercise at a higher level of performance before getting into the
relatively short term carbohydrate burning zone.
posted at 21:13 on Thu, 23 Mar, 2006 |
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All material copyrighted by Jen Schellinck. All rights reserved.