Written by Jason Peters, General Manager, O2 Fitness @ Falconbridge
Ever wonder what that diagram on the treadmill or elliptical means when it refers to a ‘fat-burning zone’? Well, there is definitely a difference in the fuel your body burns based on your intensity. Below, you will find a breakdown of the comparison of your level of intensity (% of max heart rate or HR) and which fuel your body burns as its primary energy source. There is also a correlation between level of fitness and how effectively your body burns fat as energy as well.
The information below is based on a beginning cyclist vs. an elite athlete:
50% max-HR = 500 Cal/hr = 75/25% fat/carbs = 375 fat-calories/hour
65% max-HR = 650 Cal/hr = 60/40% fat/carbs = 390 fat-calories/hour
80% max-HR = 800 Cal/hr = 25/75% fat/carbs = 160 fat-calories/hour
ELITE FIT ATHLETE
50% max-HR = 750 Cal/hr = 80/20% fat/carbs = 600 fat-calories/hour
65% max-HR = 1000 Cal/hr = 75/25% fat/carbs = 750 fat-calories/hour
80% max-HR = 1250 Cal/hr = 65/35% fat/carbs = 813 fat-calories/hour
90% max-HR = 1400 Cal/hr = 25/75% fat/carbs = 350 fat-calories/hour
Basically, the more fit you are, the more fat/hour you can burn at a higher pace. Your energy and cardiovascular system becomes more efficient at converting fat to ATP (http://en.wikipedia.org/wiki/Adenosine_triphosphate) for burning, without resorting to anaerobic fermentation and phosphocreatine at high effort levels. So the more fit you become, the more total fat-calories you burn at a higher-intensity, even though the percentage is lower compared to a lower effort.
Something to remember:
A pound of body fat equates to approximately 3500 calories. So if you have a calorie deficit of 500 calories (meaning that you burn 500 calories more than you eat each day) you would lose approximately one pound per week:
500 x 7 = 3,500
You can loosely use this equation to get a grasp on what you should be losing in a given week.
Good luck, and GET MOVING!