Fitness mode vs. fat burn mode on hrm

Ignore the zones. Work out as hard as you can maintain for the length of time you plan to exercise. You will burn more calories overall, and whole fewer will be specifically from fat, in the end you'll get more bang for your buck.

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

The only time I work to keep my heart rate down is when I'm on a long endurance run - I keep it nice and low so I can maintain the full course I plan to run, as the poster above stated. But if I'm in the gym on an elliptical, the higher the better for me. I'm there to burn as many calories as I can.

Short answer is you don't.

The so-called fat burning zone does in fact burn a higher proportion of calories from fat but, overall, burns far fewer calories which, in terms of weight loss is undesirable. Forget you ever heard the term as it's really only of real interest to endurance athletes (you have a limited amount of glycogen stored in your muscle tissue and liver but even a skinny marathon runner has, for practical purposes, an unlimited supply of energy from body fat)

^^^ THIS!!!

Here's a little more explination to what Brian was saying:

"Fat burning" mode is when your heart rate is around 50% of your max heart rate. At this level of intensity, about 50% of your calories burned come directly from fat. In "Fitness" mode, your calories burned can go down to 30% or less.

However, here's what people don't tell you.

At 50% of your max HR, you might be burning 400 calories total, per hour. That would be 200 calories burned from fat.

At 80% of your max HR (the top end of the Fitness mode), you can burn over 800 calories total per hour. That would be 240 calories burned from fat.

Now here's the kicker: The harder you push yourself, the more "damage" you will do to your muscles. this is what happens with resistance training. Your create microscopic tears in your muscles, and when they repair themselves, they get bigger and stronger. Your heart is a muscle too. It will get stronger if you push yourself harder. This repairing your body does burns MORE calories, even though you're not working out at the time.

Now, before you go out and start pushing yourself harder, you need to remember that it puts more stress on your body. Don't do it right away. Bump up your heart rate slowly (like, over weeks/months, not days) and don't increase duration/distance/intensity by more than 10% every week. If you do, you'll risk injuring yourself.

Now go out and have some fun, burning some fat!