Why do boxers wake up at 4:30am in the morning to run?

[Sharla]

While the intensity of aerobic exercise is constant, the intensity is not so great that fat cannot be used for fuel.

Whereas in any exercise where you exceed 70% of maximum intensity, fat cannot be borken down and transported quick enough to meet energy demands...therefore Glycogen will provide your energy requirements.

So yeah running (for the same length of time as a weights session) will more likely burn more calories as fat can be used as a fuel and obviously fats are more calorie dense than carbohydrates (1gram fat = 9 cals / 1gram carbs = 4 cals). Again it does depend on the intensity....but in general that's what happens.

But don't you only burn fat at much lower intensities than the average run?

I mean I swear I've read in many running mags that you need to sort of 'train' your body to burn fat for fuel for long distance events because it will still preferentially burn glycogen and carbohydrates initially - it doesn't require as much energy to break them down as it does for fat.

I'd class the average run as moderate intensity, maybe around 50-70% maximum effort would be required. Is that fair? Or would you say it's more intense?

If this is the case muscle gylcogen will will supply around half of your energy needs, the rest will come from fat. So you will still be burning fat, along with glycogen at a 50-50 ish rate.

In regards to 'training' your body to burn even more fat, as a result of aerobic training, your muscles make adaptations that improve your performance....and your body's ability to use fat for fuel improves.

Aerobic training increases the number of fat oxidising enzymes, which means your body becomes more efficient in breaking down fats into fatty acids. The number of blood capillaries serving the muscle also increases so you can transport the fatty acids to the muscle cells. The number of mitochondria also increase...(the sites where fatty acids are oxidised) so all in all you have an even greater capacity for burning fat.

Since i started studying for my diploma i've sorta fallen out with magazines. Never realised how the information was holding me back in the gym...untill i started my diploma - and started applying the proper principles.

Pissed me off that i'd wasted an awful lot of time and money buying into bad ideas that weren't backed up by any kind of science. I get the feeling that a lot of fitness magazines work off the back of 'what works for me' sorta articles...that way when it doesn't work for you they can justify it by saying 'everybody's different'.

I think i'll have to do some googling at some stage to really nut this out but i think it's pretty undispited that running uses more kilojules than most forms of exercise. I know heart rate wise I can swim really hard or do weight training at a hard intensity and not get my heart rate as high as running at a lower percieved exertion.

Also I think a lot of weight training etc - unless you do it in a circuit will make use of breaks between sets etc which would only apply to a few specific types of running workouts.

Surely if your heart rate is relatively high compared to other types of training and the kilojules burnt are also high then even if some fat is burnt you are emptying glycogen stores quite quickly too.