In the first part of this series, we covered the following points – carbohydrates in our body is a limited source of energy - provides 2,000 calories of energy. Whereas fats in our body is virtually an unlimited source close to 80,000 calories of energy. However, our body is tuned to accessing carbohydrates during endurance activities and hence the dreaded wall after a couple of hours of activity wherein the fuel sources are depleted. Long distance runners scramble to avoid this by constant loading of fuel (such as energy gels, fruits etc.) during the activity itself.
In today’s segment let’s try to look how one can access fat in our body as a source of energy.
In order for fat to fuel exercise, however, sufficient oxygen must be simultaneously consumed. When you breathe, oxygen is carried to your working muscles where carbohydrate and fat are used as fuel to create energy to keep your muscles working. The graph to the right shows an example of a typical fuel burning profile at different heart rates, wherein at a lower heart rate the body’s main fuel source is fat. This is where you will find your “steady state” where your engine is working at it’s optimal efficiency allowing you to feel strong while running. As you push yourself harder and your heart rate increases, your fat burning will at some stage drop to zero. The reason for this is simple – at high heart rates, you are taking in less amount of oxygen more often, and hence, start using more carbohydrates. The level at which your fat burning drops is different for everyone. This is linked to your age, fitness levels, genetics and hormone functions etc. Good endurance athletes have a higher fat burning graph that lasts for longer before reducing, which means they can run faster for longer before chewing into their carbohydrate stores.
> http://jupiterhealth.com.au/fat-burning-profile-key-running-faster-longer/
How does one condition in one’s body to burn fat?
Welcome to the world of “Low Heart Rate” training. Essentially you try to do a maximum of your runs at a heart rate where you burn a higher percentage of fat when compared to carbohydrates. How do I determine the appropriate heart rate for me?
There are a couple of tests that can be done to develop a curve similar to the one shown here. There are simple calculators available that arrive at an approximate estimate based on your age, current fitness status. One that I use is the Phil Maffetone method which basically subtracts your age from 180 to determine the maximum heart rate to train at.
Why would one want to try this approach?
The motivation for me is that, there is enough evidence to show that the more efficient you become in using your body fat as a fuel source, the faster you run - the holy grail for most runners!
This is because fats are a much efficient fuel source when compared to carbohydrates. Currently at a max heart rate of 130, I am clocking 13 to 14 minute miles, which I anticipate to drop over the period of next few months. I have two marathons coming up – one in August and one in February.
