ROSIE - The 'fat burning' zone

My goodness, I think the "fat burning" zone myth is the bane of every single fitness professional's life. I can't tell you the amount of times someone has said to me "but surely I need to work at a 60-70% of my maximum heart rate (MHR), as at that intensity I burn more fat?". Grrr. Grrr. GRRRR. It makes me so mad. So I see people walking, yes WALKING on the treadmill trying in vain to keep their heart rate below 70% to maximise their fat burning.

Sure, walking is a great day-to-day activity and a really good way for incredibly unfit and/or overweight people to start their weight loss journey, but as a form of fat burning exercise it certainly is not the way to go.

Here's the story behind the "fat burning zone" myth: at very low exercise intensities (60-70% MHR), a large proportion of the energy required to fuel the activity is taken from fat. However, as exercise gets more intense more energy is supplied by carbs and the proportion supplied by fat declines. At very high intensities (90%+ MHR), nearly all the energy comes from carb breakdown and almost none from fat.

But it's important to realise that actually it's the overall calorie burn that matters. At 60-70% MHR working out for an hour you will probably burn only 300 cals (depending on weight/fitness and lots of other factors). At 80-90% MHR you will burn over 700 cals per hour. It's that 700 calorie deficit you want if you want to lose weight. Also the higher the intensity you work out at, the more lean muscle mass you will tend to have. That will also maximise your fat burning potential both whilst exercising but more importantly at rest.

Also remember that the "fat max" varies enormously from person to person; there are so many variables that to put it into a 10% heart rate zone is just ridiculous.

The key to remember, the higher the intensity you can work out at the better, both for fat loss, fitness and generally to feel good!