Using Heart Rate Training Zones to Burn More Fat

Credit: Flickr/Keith Davenport

Pre-programmed cardio training zones may not be right for you

Many exercise machines and charts in commercial gyms use a common formula to give you target heart rate training zones

The common formula they use to determine your maximum heart rate is 220 minus your age.

But this formula was never intended to be used with a general population. How do I know this? One of the cardiologists who devised it said so.

The formula over or under estimates maximum heart rate for 2/3 of the people who use it. If your predicted maximum heart rate is wrong, then all your training zones will be wrong. And even a small difference of two or three beats per minute can be enough to give you an inappropriate workout intensity.

Your Body’s Energy Sources

Your body uses two sources of energy: body fat and glycogen. (For you physiology geeks, technically you have three sources as you can also use protein in certain circumstances but let’s keep it simple.)

Glycogen is energy from carbohydrates that is stored in your muscles and liver. Body fat is excess energy you store whether that comes from fat, protein or carbohydrates.  

Whenever you work out (or for that matter do anything), you’re using both body fat and glycogen for fuel. During lower intensity activities like walking you’re using more fat for fuel than glycogen. As the intensity increases you use more and more glycogen, until your reach a very high intensity when you’re only using glycogen.

A human body can store enough glycogen for up to 90 minutes of moderately intense exercise. Maybe longer, if you’re well trained. When you run out, you can’t continue at that effort level and have to slow down. This is what marathon runners call “hitting the wall” and cyclists call “bonking.” You’ve literally run out of fuel.

On the other hand, even the leanest athlete has tens of thousands of calories stored in their body fat. Theoretically, at the proper intensity, they could work out for days without stopping.

The Fat Burning Zone

By keeping your heart rate low, you’ll burn more calories from your body fat and so this intensity is often called the “fat burning zone.” But there are some misconceptions surrounding it.

Truth is, you’re in your fat burning zone all day long. While reading this blog, you’re in the fat burning zone. You’re using very little glycogen as energy (unless you happen to be reading it on your iPad while going for a run).

To lose weight or improve fitness you need to elevate your heart rate enough during exercise to burn more calories. You can stay in the fat burning zone up to 70% or more of your maximum heart rate.

On the other hand, by exercising intensely you burn less calories from fat as a percentage of your total calories. However you’ll burn more calories overall than a lower intensity workout of the same duration. And a hard workout helps elevate your metabolism so you continue to burn more calories after your workout.

Heart Rate Training Zones

Using heart rate is a good, objective way of measuring your workout intensity. Your training zones are often expressed as a percentage of your maximum heart rate.

To determine your maximum heart rate, use one of the following formulae (they are more accurate than 220 minus age):

• Men: Maximum heart rate = 208 − (0.7 x age)
• Women: Maximum heart rate = 206 − (0.88 × age)

For accurate training zones it’s best to also find out your resting heart rate (HR). Do this by taking your radial pulse first thing in the morning before you get out of bed. If you need to go to the washroom, do it and then lie down again for a couple of minutes and take your pulse.

When you have both your maximum and resting heart rates you can calculate your fat burning zone, which corresponds to an intensity of 60 – 70%, with the following equation:

• Bottom end of zone = ((Max. HR – Resting HR) x 0.6) + Resting HR
• Top end of zone = ((Max. HR – Resting HR) x 0.7) + Resting HR

Fat burning workouts should last 30 to 60 minutes or longer.

To develop your fitness you can use a training zone corresponding to 70 – 80%:

• Bottom end of zone = ((Max. HR – Resting HR) x 0.7) + Resting HR
• Top end of zone = ((Max. HR – Resting HR) x 0.8) + Resting HR

To build your fitness endurance, workouts should last 20 to 40 minutes.

The final training method you can use to really improve your fitness and performance is interval training. Using heart rate for interval training is more difficult as you’re switching between workout intensities. For intervals it’s better to use a Rating of Perceived Exertion scale, which I describe in my post on intervals.

A word of caution. Interval training is hard work. Get a thorough check up with your doctor before starting it and if you’re cleared, build a good base of fitness with the fat burning and endurance zones.

Use Variety for Best Results

What you need to do for maximum fat burning is to use all three different types of cardio workouts. Include longer, lower intensity workouts; slighlty shorter, moderately intense workouts and short, very intense intervals to develop a good level of fitness and health.