Carbohydrate/Fat Use During Aerobic Exercise

[notfreemoney]

Exercising at high intensities uses carbohydrate as the main fuel for energy. Exercising at lower-moderate intensities uses fat as the main energy source. However, exercising at a higher intensity increases metabolism for a longer period of time, burning off more calories. Higher intensities also lead to better physiological changes (overall more healthy body)

Heres what I dont understand. If someone is attempting to lose weight- they often follow the advice to exercise at low to moderate intensity ( its usually on cardio machines as a graph with heart rate on the y-axis and then a 'fat' burning zone somewhere on it). Does exercising at a low to moderate intensity really burn more fat in the long run? Im thinking that with the added benefits that exercising at a higher % heart rate outweigh the 'fat burning' intensity...

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[fitnessfreak]

exercising at a lower intensity means that the actual ratio of fat being burned relative to other fuel sources is higher. when you exercise at a higher intensity the percentage amount of fat you are burning goes down. however, even though the percentage amount of fat being burned drops as you increase intensity, the actual amount of fat being burned is still increasing in real terms.

so to sum it up. exercising at a higher intensity will burn more fat, so if you are focusing on fat loss, the best move is to exercise at the highest intensity you can handle for an extended period of time. and of course, exercising at a higher intensity does have other benefits, such as improved cardiovascular fitness.

disclaimer: im no expert and i cld be wrong, but i have been reading a lot of articles and stuff on this issue and that is the conclusion i came to.

[Efourdee]

Very well stated fitness freak.

But an important note to add is that the one of the other fuels being burned at high intensity are muscle. People workout at low intensity to burn fat while preserving muscle.

[ottsville]

Notfree: most people are not in any type of condition to train at a high intensity, especially if they are just starting a regimen. The average person won't and shouldn't jump off the couch and say "I need to lose weight so I'm going to run as far as I can at max speed." Many won't after long periods of base training either. That type of workout will not keep the interest of 99% of the people who are trying to lose weight in addition to the increased risk of injury. I believe that most people workout at intensities that may not optimize their weight loss, but at intensities that will keep them interested.

Fitness described some basics, but there are lots of new studies in this area. Some recent studies are now showing that interval type workouts are more efficient at burning fat than either a lower/higher intensity. From what I've read though, there seems to be a lot that is specific to the person/situation.

One thing that has helped me to get more of a grasp on workout stuff like this is to understand some basic nutrition and chemistry of fueling muscles. I would do some research on glycogen stores, lactate threshold, anaerobic threshold, nutrition for athletes, and recovery meals for starters.

[SmokeyRidesAgain]

[ QUOTE ]
Very well stated fitness freak.

But an important note to add is that the one of the other fuels being burned at high intensity are muscle. People workout at low intensity to burn fat while preserving muscle.

[/ QUOTE ]

Is intensity a function of heart rate while exercising compared to max/resting heart rate? Low intensity being a small increase in bpm, high intensity being near/pushing your max? Or is it a measure of something else entirely? I exercise quite a lot but I'm not that knowledgable about this side of it.

[Efourdee]

The function used to measure is your VO2 max.

VO2 max is the maximum capacity to transport and utilize oxygen during incremental exercise.

Heart rate is corrolated, but depending how fit you are will depend how fast you get your heart rate going with any given intensity.

[SmokeyRidesAgain]

Thanks, I should have remembered that.

[notfreemoney]

Smokey,

VO2max is highly correlated with max HR. If you figure out the percentage of HRmax you want to work out at using the formula 220-age (or better yet look up the karvonen formula which takes into account resting HR) it will be around the percentage of your VO2max.