How much fat am I burning when I exercise, compared to carbs and protein?

Question

My heart rate is usually around 135-145 bpm, which is about 65% of my max heart rate. The workouts always consist of a 1 or 1 and a half hour bike ride (14mph). I think I'm burning around 500-600 total cals per hour doing the biking, so what do you think the breakdown of fats/carbs/proteins would be? Also, would it change if I had just eaten a meal before hand?

Answer 1

The amount of sugar you're burning is determined by the amount of EFFORT you are putting in. More effort, more sugar, because sugar is an explosive chemical, and is used to add power to a movement.

(Protein isn't used as a fuel for muscle movement)

So If you want to maximise fat use, turn the effort down. Movements that use ONLY fat, can be continued round the clock without making you tired and hungry.

Working at 65% VO2Max (which may not be the same as 65%MHR depending on how you calculated that) will make good use of fatty fuel, but operating at less than 50% works even better.

What you do the rest of the time, will also affect your muscle fibre 'recruitment' (and therefore your fuel use). If you get to the gym feeling knackered, you will have to push harder to do the same work. This can convert a 'slow-fibre' workout (gentle, burning fat) into a 'fast-fibre' session (kicking hard, burning sugar).

Doing a harder workout, in order to burn more calories, is a 'false economy'. You will use more sugar by working harder, so the extra calories you use up will be replaced as your appetite increases. 'Recovery' processes are mainly powered by sugar, too, so the extra 'metabolism' between sessions won't help you to get rid of bodyfat, either.