You may have heard of heart rate training zones and how elite athletes, and more recently a growing number of recreational athletes, use them to guide their training.

This blog explains why they are important for your training and how each one can help your body evolve and grow based on your training and competition goals.

What are heart rate zones?

Heart rate training zones reflect your body's metabolic status in different training intensities. They are heart rate ranges (e.g., 123 - 142 beats per minute), each one corresponding to an exercise intensity, where your body responds metabolically in a specific way. Two factors determine the metabolic state of your body in each zones:

1. The fuel mixture used (i.e., the balance between fats and carbohydrates).
2. The physical traits your body develops when training in this zone.

For example, when training in zone 2, your body will burn the most fat and enhance its cellular health fat-burning capabilities at the fastest rate. 

What is “fuel ratio” and how does it help determine training zones?

During exercise, your body typically burns a mixture of fats and carbohydrates to release the energy required (i.e. calories) for movement. As intensity increases, your body shifts between fuel sources to compensate for increasing energy demand. Fat releases more energy than carbs (i.e., 9 kcal per gram of fat vs 4 kcal per gram of carbs) but it has a slower burning process making it the preferred fuel for lower exercise intensities. Carbohydrates require less time to burn and can therefore support higher exercise intensities where the rate of energy demand is larger. The mix of fats and carbohydrates used by your body is revealed by the breakdown of oxygen and carbon dioxide in your breath and is measured through the use of a metabolic analyzer like PNOĒ. Figure 1 shows the difference between fat and carbohydrate burn as exercise intensity increases during a treadmill test.

Figure 1 Dark green: fats, Turquoise: carbohydrates, Light green: heart rate

Since this measurement requires you to wear a mask, information for your body’s fuel usage becomes almost impossible to obtain during everyday training. As a result, we use heart rate as a proxy metric to accurately estimate our body’s fuel usage and metabolic status. This is done through a metabolic test whereby measuring heart rate and the fat-carbohydrate mix you can establish the correlation between fuel mix and heart rate. We refer to this as “getting your personalized training zones”. However, it’s important to note that the correlation between heart rate and fat-carbohydrate balance depends largely on the type of exercise. For example, you may be burning 30% fats and 70% carbs at 140 beats per minute when running but only 15% fats and 85% carbs at 140 beats per minute when cycling.

How many training zones do we use? What physiological traits does each one train?

The 5 zones system is the most frequently used one which accurately captures the difference in metabolic states while remaining practical enough for everyday usage. Each zone is used for a different purpose as it inflicts different metabolic adaptations on your body

Zone 1

Training intensity is typically used for warmup or active recovery (i.e. recovering from intense exercise while moving)

Zone 2

Zone 2 training is important for overall health, fitness and performance. Zone 2 develops mitochondrial function and improves fat-burning efficiency. Everyone should be doing some Zone 2 training. Improved mitochondrial function supports recovery, insulin sensitivity, and helps you utilize fuel more efficiently during your high-intensity training sessions which improves athletic performance.

Zone 3

Zone 3 training can help strengthen your respiratory muscles and improve cardiovascular function. It’s an ideal intensity when suffering from a lung or heart problem since its moderate- intensity offers a strong stimulus to the heart and lungs without being exhausting or overly strenuous.

Zone 4

Zone 4 training will help improve your VO2max and ability to sustain high-intensity exercise for prolonged durations by improving lactate shuttling. Lactate is a byproduct of anaerobic metabolism which can be also used as fuel by your muscles. The more efficiency your body can clear fatigue byproducts the longer the activity/exercise remains sustainable. As a result, the greater your lactate shuttling capability the greater your ability to sustain high exercise intensities for long periods of time. This zone is extremely important for performance in many sports including Crossfit and endurance sports.

Zone 5  

Zone 5 training will improve your VO2max and peak power output capability (e.g. maximum speed or cycling wattage). This exercise intensity is sustainable for 60 to 120 seconds and requires one to train at his maximum potential. This is your max HR range and it must be targeted for training if you expect to perform at extremely high intensities.

Why should I care about training zones?

Take Home Message: Regardless of age, gender, and fitness level, every person has one or more systems posing a limitation to fitness or health. Targeting these limitations effectively requires the precision of focusing your training to the zone(s) that will bring about the adaptations needed for you, to overcome them.  

The PNOE metabolic analyzer provides gold-standard accuracy in determining your training zones.  A PNOE trained representative can help develop an exercise training plan that puts them to effective use.

Understanding how your body responds metabolically and building a program that is individualized to your metabolism is a foundational step towards maximizing your workout’s efficiency and achieving your health or performance goals faster and with less effort.