By Dev K. Mishra, M.D.
President, Sideline Sports Doc
Medical Director, Apeiron Life
Clinical Assistant Professor of Orthopedic Surgery, Stanford University
February 25, 2020
- In zone 2 heart rate exercise you’ll preferentially use fat for fuel, making this a very effective way to lose body fat
- There are several ways to know whether you’re in zone 2
- Exercise in zone 2 for 150 minutes per week for body fat loss
I’m a big believer in high intensity interval training as a very effective way to improve cardiovascular fitness. But to lose fat your best bet would be to use zone 2 heart rate training. Zone 2 is not only effective in helping you lose body fat, but also has great benefits to improve glucose sensitivity and reduce heart disease risk.
The reason zone 2 training is so effective is due to the fuel (fat) used by the muscles during this type of training. In today’s post I’ll provide a brief description of the science behind fat burning in zone 2, how to know whether you’re in zone 2 during training, and how much time you should spend in that zone each week.
What is “zone 2” training and why does it work?
Exercise physiologists divide efforts into 5 or 6 “zones” depending on metrics such as blood lactate or heart rate. For heart rate zones you’ll commonly see 5 zones based on a percentage of maximum heart rate. Zone 2 is generally recognized as 60% to 70% of HR max, zone 3 from 70% to 80%, zone 4 from 80% to 90%, and zone 5 from 90% to 100%.
I’ve heard for many years that zone 2 is the most effective for fat burning but no one has been able to give me a good explanation of why that is. But recently I came across Peter Attia’s podcast featuring Inigo San Millan of UC Boulderwhere an elegant explanation was provided. In zone 2, slow twitch type 1 muscle fibers are activated, and these fibers use fat for power.
So if you want to lose fat you’ll want to exercise in zone 2 because fat is used for fuel. Zone 2 training is also known to improve metabolic syndrome, type 2 diabetes, and reduce heart disease risk. There’s a lot to like about zone 2 exercise.
How to know when you’re in zone 2
Most people will either use some form of heart rate measurement, or a no-equipment method with perceived exertion. From most sophisticated to least sophisticated, here are some ways to determine your zone 2:
- Physiology laboratory testing. Without a doubt this is the most accurate but also the most involved method. While either running or cycling in a highly controlled environment you’ll have some combination of blood lactate testing, and also a measurement of Functional Threshold Power (cycling) or Threshold Running Pace. If you’re an elite endurance athlete this is the best way to go.
- Heart rate zone estimation with chest strap or wrist-worn heart rate monitor. Devices made by Polar, Garmin, Apple and others can estimate your maximum heart rate and then calculate when you’re in the 60% to 70% range roughly corresponding to zone 2. I use a Garmin Fenix 5S and find this to be a great way to know when I’m in various training zones with an easily readable display on the watch. Highly recommended for the serious amateur.
- Count your pulse with a standard watch. First, get an estimate of your maximum heart rate with this formula: 208 – (0.7 x age).That formula is more accurate than 220 – age. From the maximum, multiply by 0.6 for the low end of zone 2 and multiply by 0.7 for your upper end. After about 10 minutes of exercise stop, count your pulse for 15 seconds, and multiply by 4 for your heart rate. Adjust your exercise intensity to stay in zone 2.
- Use your personal estimate of exertion and a “talk test”. On a zero to 10 scale make an estimate of how hard you’re exercising, with “10” being the most intense thing you can imagine. In zone 2 you want to be about 5 or 6. You should be able to talk and hold a conversation but not necessarily to sing a song. That’s the talk test. This will do if you don’t have another option.
How long should you exercise in zone 2 each week?
For fat burning and general body fitness it’s recommended to do 150 total minutes in zone 2 per week. This will be helpful in your body composition, and will also help with other positive effects such as improved glucose sensitivity and good heart health. If you have type 2 diabetes you may want to go as high as 300 minutes per week.