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Perhaps you’re already someone with a regular exercise habit and a good knowledge of how to design an effective training program. This is step one to reach athletic success, whatever your goal may be. However, if you really want to optimize your outcomes — whether that be fat loss, metabolic health, speed, or stamina — paying more attention to your workout intensity is an absolute necessity.

Obviously, you can measure workout intensity using subjective measures like perceived exertion, the “talk test,” how fast you’re running, or how much weight you’re lifting.

But the gold-standard way to gauge effort is by using heart rate. Heart rate provides insight into the physiological demands of your workout. Higher efforts require more blood flow, demand greater amounts of oxygen, and force the heart to pump more blood at a faster rate. Thus, the more intense the workout, the higher your heart rate will be.

Planning and performing your workouts using heart rate as a guide is the single best way to fine-tune your training plan.This is done using pre-defined heart rate zones that are personalized based on your own heart rate.

The benefits of training using workout zones are numerous. Zone training is the best way to gauge your progress — when you’re able to go faster or further in the same zone or at the same heart rate, it’s an indication you’ve gotten fitter.

Workout zones also allow you to target specific goals for each workout, whether it be increasing fat-burning capacity, improving your lactate threshold, or elevating your VO2 max. Fitness, metabolic flexibility, and body composition can all be targeted by using workout zone training. Zone training also can decrease your chances of experiencing burnout or injury from doing too many high intensity training.

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How to find your maximum heart rate

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Before setting out to define the workout zones, it’s important to calculate or estimate your maximum heart rate. Most workout zones are calculated based on a certain percentage of your maximum heart rate — which can be influenced by factors including genetics, age, sex, and training status. Not everyone’s maximum heart rate is the same, so it’s important to calculate it based on your personal characteristics.

Unfortunately, getting a true maximum heart rate can be difficult and usually requires doing a test in a laboratory. During this test, you’ll run to exhaustion, and the highest heart rate you achieve is considered to be your max. While it’s possible to do an at-home test to determine your max heart rate, there are also equations that can be used to predict your max heart rate based on your age. While some error exists in these estimations, than can provide you with a somewhat accurate measure of your max heart rate.

There are two popular equations used to calculate max heart rate. The first is called the Fox equation. In this equation, your max heart rate is simply 220 - your age in years. 

For a 35 year old, this equation provides a max heart rate of 185 (220-35) = 185.

The second is the Tanaka equation. In this equation, your max heart rate is calculated as 208 - 0.7 x your age in years.

For a 35 year old, this equation provides a max heart rate of 183 (208 - [0.7 x 35]) = 183.

These provide very similar heart rates, so either equation may work for the purposes of determining your heart rate zones.

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Workout zones defined

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Most workout zone frameworks utilize a 5-zone model, and some people like to add a “sixth” zone known as zone 0. 

Zone 0

A recovery zone below 50% of your maximum heart rate, where there is very little stress being placed on the body.

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Zone 1:

50-60% of maximum heart rate

Zone 1 is described as a very light effort. This is the zone you’ll target when warming up, cooling down, or engaging in active recovery between sets or intervals.

In theory, you could spend 1-6 hours or more in zone 1. Most of the energy used in this zone will come from burning fat.

Zone 1 could also be the intensity of your recovery day — perhaps a light walk or spin on a stationary bike. While you’re still promoting blood flow to muscles and increasing metabolic rate in zone 1, the demand on the body is very low.

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Zone 2:

60-70% of maximum heart rate

Zone 2 is described as a light effort — something you could hold comfortably for hours. Zone 2 is also the zone where you start to reach your maximum fat-burning capacity, though you’ll still be using some carbohydrates for fuel.

Zone 2 training is perfect for building a strong aerobic base, increasing fat-burning capacity, building more mitochondria, and improving endurance. High-level endurance athletes spend a lot of time training in zone 2 — it’s the foundation around which all other training is built.

Zone 2 training has also been getting a lot of attention due to it’s potential benefits for healthspan and longevity. It’s the sweet-spot zone for those looking to balance training for performance and training for health.

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Zone 3:

70-80% of maximum heart rate

Zone 3 is described as a moderate intensity — you could exercise in this zone for around 1-2 hours. In zone 3, the body is deriving around half of its energy from fat and half from carbohydrates. 

Like zone 2, zone 3 is great for building a strong aerobic base and improving endurance. However, because it’s more intense, it’s best not to spend as much time training in zone 3 as you do in the lower, easier zones.

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Zone 4:

80-90% of maximum heart rate

Zone 4 is the zone where you reach what is known as the lactate threshold. This is the point where the body begins to accumulate lactate — which is formed during the breakdown of glucose, the major fuel source used in zone 4.

It’s important to note that lactate can be used by the body as a fuel. However, at the lactate threshold, we are producing more lactate than we can clear, and some begins to accumulate, leading to a metabolic state that starts to limit performance.

Zone 4 training is great for improving your ability to clear lactate, elevating your lactate threshold, and building muscular endurance. Examples of zone 4 workouts include tempo runs and threshold intervals.

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Zone 5:

90-100% of maximum heart rate

Zone 5 is max-intensity training. At zone 5, you’re exercising at or above your VO2 max and the intensity is something you can’t maintain for more than 5 minutes or so. This zone will leave you breathless — literally.

Zone 5 is fueled almost exclusively by carbohydrates, meaning a lot of lactate is being produced, making the workload unsustainable for very long. That’s why a majority of exercise done in zone 5 comes in the form of short, high-intensity intervals of max or near-max efforts. 

The benefits of zone 5 are extremely robust and include improvements in VO2 max, increased strength and power output, and better glucose tolerance. But this type of training shouldn’t be done often because of how much of a stress it imposes on the body.

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The benefits of polarized training

How much time should you spend in each zone to optimize the benefits of your training program? This is a question that’s puzzled physiologists and sport scientists for decades. However, data from elite athletes have helped to popularize a training framework known as the “80/20” training principle that has been well-accepted in the training community.

The 80/20 principle, also known as polarized training, suggests that about 80% of your total training volume should be spent in zones 1 and 2 — well below lactate threshold. 

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The rest of your training — 15 to 20% —  should be made up of the more intense interval sessions and threshold work in the higher zones.

The purpose of polarized training is two-fold. For one, it can be a great preventative measure against burnout or “overtraining.” Limiting your weekly volume to less than 20%  high-intensity work is a way to press on the breaks. Going too hard too often might feel good temporarily, but can eventually lead to injury or a loss of motivation.

Polarized training is also a sustainable way to maintain a healthy aerobic base year round. Not only will this benefit you when you’re competing, but it will also allow you to keep high energy levels on a consistent basis.

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Start training with workout zones

Starting to train with workout zones is simple and might not even require you to make drastic  changes to your current training plan. Calculate your zones now, and you can start training with zones on your very next workout, as long as you have some sort of device to track your heart rate.

These zones are also easily color coded in your Basis app. Optimizing your energy starts with knowing your body in and out. Workout zones are one way to jump-start that process.

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