Fat burning zone. You may have noticed that some bikes and treadmills at the gym have a setting that says "fat burning zone", which implies a setting for intensity or speed. The reason for this is that the body burns a greater percentage of fat at a slow pace (or after about 90 minutes of exercise). The fat burning zone, a low intensity speed zone is mainly a gimmick, and here is the reason.
Even though you burn more fat going slowly, you still burn a percentage of fat at much faster speeds or intensity. It all boils down to how much energy you expend in totality. For example, if you compare exercising at a slow rate that burns 60 percent fat and 40 percent glucose and a higher intensity or duration that burns only 30 percent fat and 70 percent glucose, you may still burn more fat at the higher intensity.
A typical example. Exercise (1) is the slower 60/40 mix and exercise (2) is the faster, 30/70 mix of fat and glucose fuel.
1. Walking on a treadmill for 30 minutes -- 180 calories used -- 108 calories of fat burned
2. Running on a treadmill for 30 minutes -- 400 calories used -- 120 calories of fat burned
You can see from this example that the bottom line really is how much energy you expend -- and that is the ultimate fat burning measure. The theoretical fat burning zone is mostly a convenient myth.