Quote Originally Posted by ono View Post
Quote Originally Posted by Sharla View Post
Quote Originally Posted by ono View Post
Generally speaking, the higher the exercise intensity, the greater the reliance on muscle glycogen.

During anaerobic exercise (sprints, heavy weight-training etc...) muscle gylcogen , rather than fat, is the major fuel.

During aerobic exercise, you will use a mixture of muslce glycogen and fat, for fuel. Exercise at a low intensity is fulled mainly by fat. As the exercise increases, you will begin to use a higher proportion of muscle glycogen than fat. Moderate intensity exercise (50-70 % volume max), muscle glycogen supplies about half of fuel...the rest coming from fat. If your intensity exceeds about 70% max effort, fat cannot be broken down and transported fast enough to meet energy needs, so muscle gylcogen provides at least 75% ish of your energy needs.

Carbohydrates at night is a debatable subject. If muscle glycogen levels are low because you haven't re-fuelled sufficiently, fat gain is not an issue. Consumed carbohydrates will go to replenishing glycogen levels. Fat gain is only a worry if glycogen levels are full and you continue to consume carbohydrate during a period where they aren't required for exercise.

Protein is important for muscle repair but the guidelines provided in fitness magazines/websites etc... that tell you to eat ludicrous amounts of protein are misinformed. An absolute maximum of 2g per kg bodyweight should be consumed daily. Excess protein cannot be stored, therefore it must be broken down into waste products. Each amino acid has an amino group and an acid group. The amino group contains nitrogen, which is first converted to ammonia, then to urea where it passes from the liver to the kidneys...where it is pee'd out. The acid group is converted to carbohydrate and used for energy. Any excess will be stored as bodyfat.

You will not recover from a weight-training session by limiting carbohydrate. Eventually protein will have to be broken down and used for fuel as there will be a lack of muscle glycogen.

I think people get worried about consuming carbohydrates because of all the fad diets out there. I was reading today about a swimmer in the olympics who consumes 12,000 cals a day. That's a lot, and he has very low bodyfat levels.

If you're exercising daily and intensely carbohydrates are very important.

Anyway i'm not even sure if i've answered your questions...i've just ranted. Anyway hope you find it quite helpful.
Very interesting thanks Ono

You have answered my Qs I think. I don't know why I always assumed aerobic exercise would burn more glycogen - maybe because running tends to burn a lot of kilojules compared to weight training etc. Maybe I think that it will be more likely to empty glycogen stores in one session than weights - could that have any relevance?

I actually really got a lot out of your post though - wanted to rep you but I have to spread it!

Glad you started sharing all this thanks!
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.