Whats the diff between fat burn and cardio

I believe the fat burn button is when the machine keeps your heart rate at the target heart rate zone, and that's why it was keeping you at a hb of 120. Personally, I would not choose that program because you end up burning less total calories.

From a machine standpoint, the difference is just the default setting they use for providing a "target" heart rate.

For a "fat burn" program, the machines defaults to 55% or 60% of age-predicted maximum heart rate and "cardio" defaults to 75% or 80%.

If you want to know why the machines are programmed this way--there will either be other comments explaining it in this thread or you can google "fat burning zone myth" and get lots o' info.

While there is some benefit to including lower-intensity endurance cardio and higher-intensity cardio in your routine, I recommend not using these settings at all. Number one, there is so much variability in max heart rate that there is only about a 50-50 chance at best that the heart rate they suggest will be the right one for you. Secondly, heart rate "drifts" upward during a longer cardio workout, even with no increase in workload. So, because your heart rate drifts up out of the "zone", the machine will continuously lower your workload, thus leading you to burn fewer calories, and get a lessened training stimulus. Kind of defeats the purpose.

The intensity of the workout determines where the body tries to get its fuel from. At a lower intensity it has time to convert fat for energy. At higher intensities it gets it from more readily available sources.

http://exercise.about.com/od/weightloss/a/The-Truth-About-The-Fat-Burning-Zone.htm

i stick to cardio.. fat burning zone might burn a greater percentage of fat calories, but you burn more overall calories (and often more fat calories) on cardio. the broscience i've seen says that it's 60% of fat calories from fat burning zone vs 30% at a higher intensity.

but in the end, what's a larger number, 60% of 400 calories (what i'd burn during a 60 minute fat burning zone cardio session) or 30% of 800 calories (what i burn during a typical kickboxing class that's higher intensity)?

my personal plan is to go as hard as i can for as long as i can, recover a bit, then pick up the intensity for as long as i can. i dont pay attention to heart rates or what zone i'm in

Secondly, heart rate "drifts" upward during a longer cardio workout, even with no increase in workload. So, because your heart rate drifts up out of the "zone", the machine will continuously lower your workload, thus leading you to burn fewer calories, and get a lessened training stimulus. Kind of defeats the purpose.

Interesting. I had noticed that my heart rate does indeed go up after a while, even when using a constant speed on the treadmill. Its good to know that this is typical.