One thing that has always gotten under my skin is this whole fat burning “zone” thing. The majority of people don’t really understand the big picture. The fat burning zone is a zone specific heart rate that causes the person to burn the highest percentage of fat from calories instead of burning carbohydrates (sugars) or protein (muscle) while exercising. After all most people are exercising to burn fat and not to burn muscle or carbohydrates. So for instance say you calculate your optimal fat burning zone and find out your number is between 125-135 bpm (heart beats per minute). This means to burn the highest percentage of calories from fat while doing your cardio you would need make sure not go above that number of heart beats per minute or you will start burning more carbohydrates and protein (muscle) to supply the energy from a percentage standpoint. But these numbers can be misleading. Do you know when you burn your highest percentage of calories from fat? You probably would never think of it. But it is when you are asleep. You see it takes oxygen to burn fat. If there is no oxygen then your body has to burn sugar for energy. So in that respect if your say running full speed or high intensity cardio, your oxygen levels are limited and you burn a higher rate of carbohydrates (sugar) and less percentage of fat. So say to do cardio in the fat burning zone you want your heart rate to be around 65% max so that your burning calories yet still have enough oxygen to burn the fat. So it seems to be the most efficient way to burn fat if you exercise in the “fat burning zone” without your heart rate going over 70% which would mean oxygen limitations. But there is so much more to it then this and so many people and fitness enthusiast miss the big picture. For example lets say you do do cardio or exercise and keep your heart rate moderate and in the 65% zone for 45 minutes. Say your burn 400 calories and 40% of those calories come from fat. So that would mean that of those 400 calories 160 of them was suppossedly fat. Remember these numbers are just figures to prove a point. So that is a pretty high percentage of calorie burning coming from fat. So what if you do cardio way above the fat burning zone for 30 minutes, 15 minutes less than the above example and because your putting more effort you burn 900 calories but now your only burning 20% calories from fat because of low oxygen. That would be approximately 180 calories burned from fat. So you got to exercise 15 minutes less and still burned a few more calories from even though the percentage of calories is cut by 50%. So lets look at it in chart form.
Cardio in zone at 65% heart rate for 45 minutes = 400 calories burned= 40% from fat (160) calories from fat.
Cardio zone higher heart rate 80% for 25 minutes = 900 calories burned = 20% from fat (180) calories from fat. (also you are cutting workout time in half).
But wait the discussion doesn’t stop there. Who cares how much fat you burn during the actual exercise!!! What about post workout fat burning. Who cares about the 25-45 minutes you spend exercising. You actually burn much more fat for several hours after you leave do to the exercise speeding up your metabolism. Also studies show that the higher intensity the workout the longer your calorie burning lasts (as much as 8 hours worth), as opposed to lower intensity workouts. So depending on your goals you will need to decide which way is better for you but don’t get so caught up into this fat burning zone stuff and be more concerned on which way burns the most fat overall during a 24 hour period and week to week, month to month.