[Jetter2]

Originally Posted by Sportsmedjosh

To find out what you are using as an energy source we use something called RER or RQ, which looks at o2 vs co2. It is collected and measures, the range is from .07 to 1. closer to .07 means all fat is being used while 1 means all carb. Though there are some considerations to look at while doing this, such as hyper ventiliation.

But to answer your question, programs on cardio machines take infomation that is collected from RER, RQ, Vo2 max studies and use an equation that will help determine where you should be if you are at a certain point in HR, age, weight.

Its close but it's not dead on. There are three sources of energy your body uses
ATP CP
lactic acid (anaerobic)
aerobic

each gets it's energy source from a different system and takes a different amount of time for them to kick in. It's also important to know that fat burns in the flame of a carb meaning if you don't have enough carbs your body will not use fat effic. If you have a prolonged cardio session at a low intensity your body will tend to use more fat as an energy source since fat (lipids) yield the most amount of energy per gram (9).

I was waiting for ur reply, thx for the info!