Zone 2 training is aerobic training for longer periods (45-90 minutes) at a lower intensity (still able to speak).

In Max Workout we’ve focussed a lot on reduced exertion high-intensity interval training (REHIT), where the intervals are super intense and as short as 20 seconds. We’ve also talked about high-intensity interval training (HIIT) where the intervals are generally longer, but less intense.

Both are great at getting you fitter and healthier in the minimum amount of time. Awesome.

Zone 2 training is the opposite of REHIT. Instead of intense bursts of activity followed by recovery periods, Zone 2 is getting faster by slowing down. Slow down to get healthier. That’s not a message you hear often.

No pain, no gain. We’re used to hearing that. Zone 2 training is a big switch in thinking as the pace is a lot slower than you’re probably used to. Yet your body craves this pace and rewards it accordingly.

What are the advantages of Zone 2 training?

  • Zone 2 training improves your muscle's mitochondrial function by increasing its metabolic efficiency and increasing its capacity to burn fuel—fat, glucose, lactate—for energy. This optimizes your metabolic health and heals metabolic dysfunction.
    • A common thread in Type 2 diabetes, obesity, cardiovascular disease, and Alzheimer’s is mitochondrial dysfunction.
    • Mitochondrial dysfunction is when your mitochondria are not working properly or as efficiently as they could be. When mitochondria are not working properly we cannot burn glucose, which builds up in the blood.
    • When excess glucose builds up, it can lead to all the problems mentioned earlier. Managing glucose through diet and exercise is crucial for increasing longevity.
  • Zone 2 burns more fat than any other form of exercise. If you have a lot of weight to lose, try Zone 2 training.
  • The more Zone 2 training you do the better you are able to uptake glucose, improve insulin sensitive, and become more carbohydrate resistant.
  • Zone 2 improves your ability to counteract damaging processes due to inflammation, which is often the result of excess fat.

If you'd like to learn more about mitochondrial training take a look at Reprogram Your Mitochondria for Long Life and Robust Health Using Max Workout.

Why is it called Zone 2?

Zone 2 is based on the idea of heart rate training as a guide for intensity. Heart rate is measured in beats per minute (bpm) or as a percentage of your maximum heart rate (MHR).

There are 5 zones:


So, Zone 2 training is exercising at 60 percent to 70 percent of your maximum heart rate. In perceived exertion terms, this maps to Comfortable Pace. You want a pace where you’re right on the edge of being able to hold a conversation. It’s your highest output while still being able to maintain a conversation. Are you a world class marathon runner? It’s likely your pace will be a lot faster than for your average person, but for each person, their pace should be appropriate for their level of fitness.

Measuring lactate is a scientific way to calculate your personal Zone 2 pace, but since most of us don’t have access to a lactate meter, we’ll use the less formal methods of heart rate and perceived exertion.

In the zone scheme, Zone 5 training probably maps to REHIT workouts, and Zone 4 training mostly maps to HIIT.

Calculating your Zone 2 Target Heart Rate

This is tricky. There are a lot of different possible methods:

  • The most scientific method is to get a lactate meter. The target is for a lactate reading of near, but still under 2 millimolar.
  • Use a services to determine your Zone 2 heart rate for you. They do this by running a lot of tests on you.
  • A large number of algorithms are available for determining your Zone 2 target heart rate. The simplest is (220 - age) * .65.

You can always fallback on using the perceived exertion test: go at the highest pace where you can still maintain a conversation. Any higher and you're probably burning glucose for fuel instead of fat.

The Biology Behind Zone 2

There are three types of muscle fibers: Type 1 (slow-twitch), Type 2a (moderate fast-twitch), and Type 2x (fast-twitch).

For more information on the muscle fibers you might like:

“Twitch” refers to the contraction, or how quickly and often a muscle moves.

Type 1 fibers, slow-twitch fibers, are the smallest fiber types with a darkish red color. It has a fairly slow twitch speed and produces a relatively small amount of force when contracted. It has high amounts of mitochondria, which are organelles within each cell that uses oxygen to produce energy. We’ll talk more about mitochondria a bit later. Type 1 fibers are highly fatigue resistant, allowing them to be active for long periods of time. They are the primary fibers used during low-intensity activities like walking, jogging, or aerobics.

Type 2a fibers, moderate fast-twitch fibers, are red and intermediate in size. These larger fibers use a combination of oxygen and glucose as a source of energy. This combination allows for quicker contracting speed and higher force output compared to type 1 fibers. The tradeoff is fatigue resistance isn’t as high, which is why they’re activated during anaerobic activities that are moderate in duration, like a mile run, swimming, and short-distance cycling.

Type 2x fibers, fast-twitch fibers, are white in color because of their low oxygen capacity, and are the largest fiber type. They have extremely high levels of glucose stored as glycogen, producing the fastest twitch speeds and most force. The tradeoff is the fiber fatigues quickly, burning out after 15 to 30 seconds. These fibers are recruited for high-impact, heavy resistance activities, like lifting weights and sprinting.

For any activity, muscles are recruited in a certain order: Type 1 fibers are recruited first. When they’re maxed out, Type 2a fibers are activated. After they max out, Type 2x fibers kick in. The idea is to reduce fatigue and increase motor control by minimizing the force necessary to complete a movement.

How do muscle fiber types relate to Zone 2?

Zone 2 workouts stimulate slow-twitch muscle fibers to the fullest. You want to stop right before you start recruiting faster twitch muscle fibers (which burn glucose). This is also where you burn the most amount of fat—by recruiting the most number Type 1 muscle fibers.

Why? Type 1 muscle fibers have the highest mitochondrial density, so you’re really stimulating them a lot with Zone 2 training. You body switches to using fast twitch muscle fibers, when the energy demand can’t be met using fat and you need to switch to a different fuel. That switch triggers a decrease in fat utilization and a switch to using glucose for fuel. We also see the increased production of lactate as glucose is used for fuel. This is why Zone 2 training is at a slower pace. Any faster and you switch to burning glucose.

Zone 2 training is a better weight loss plan than calorie counting. That's because when you train too hard you're burning glucose, not fat. It's not fair, but when you work really hard, you burn near zero ounces of fat. Zone 2 to the rescue. With Zone 2 training you're training and reprogramming your mitochondria to become better at burning fat. That's the perfect diet. No calorie counting and you burn fat. Best of all, since Zone 2 exercise is at such a low level of intensity, it's a form of exercise you truly can do for the rest of your life.

Zone Training Tips

Do what?

  • Pick an activity like a treadmill or stationary bike, where you can maintain a slow and steady pace for a long period of time. Biking or running outside may make it difficult to maintain a Zone 2 pace because of the uphill or downhill sections. Remember, you don’t want to slip into burning glucose. You want to burn fat for fuel and that requires a Zone 2 pace.
  • Weight training is not enough to retrain your mitochondria.
  • It’s generally better not to mix training of different zones in one workout. Pick what you want to improve and stick to it.
  • If you want to lift weights on the same day as a Zone 2 workout lift after the Zone 2 workout. Make sure there’s a couple of hours between the workouts.
  • If you want to combine Zone 2 and Zone 5, perform a Zone 2 workout first, followed by a couple of REHIT intervals.
  • Do both Zone 2 and Zone 5 (REHIT and HIIT) training. HIIT at somewhere around 90-100% VO2 max also improves mitochondrial function.
  • Zone 2 tends to be activity specific. Changing activities means you probably won’t make as much progress as when choosing one activity. You’re simply not as efficient at activities you don’t practice. So pick an activity you enjoy, like walking, and stick with that.
  • All you need to do is walk an hour a day to keep your mitochondria healthy, especially if you want to eat more carbohydrates.

How often?

  • Are you not in good condition? Start at 30 minutes three times a week.
  • Zone 2 two days a week is effectively a maintenance dose. You may not see improvement, but you’ll arrest any decline.
  • Zone 2 three days a week starts to move the needle on improving your health.
  • Zone 2 four days a week, 1 hour - 1.5 hours per day, is an ideal target for someone who is not just starting out and is not an elite athlete.
  • Zone 2 five days a week is necessary for elite athletes to show improvement.
  • Mitochondria are very plastic. They respond to training. But the downside side is when you stop Zone 2 training, you’ll lose gains. Training benefits may disappear in as little as two weeks. When elite athletes stopped working out for 2 months, their mitochondrial function decreases by 40%. What happens if you haven’t exercised in 20 years?
  • When you eat, do a Zone 2 workout right away as that burns the glucose in your system.

How long?

  • Short intervals are not as effective as longer intervals.
  • A Zone 2 session should be a minimum of 45 minutes with 60-90 minutes being an ideal target.
  • Remember, as you get more fit your heart rate target may increase.

Learn More