The benefits of training with training zones.

You must have probably heard of heart rate training zones and how elite endurance athletes, and more recently a growing number of recreational athletes, use them to guide their training. Heart rate training zones are a reflection of the metabolic states your body undergoes in different training intensities. In simple words, 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. Your body responds metabolically in different ways depending on the intensity you are exercising. These differences are determined mainly by two factors:

• The fuel mixture used in specific exercise intensity (i.e. balance between fats and carbohydrates)

• The capabilities your body develops when exposed to that intensity

Let’s look into these two factors in greater detail and how they provide the criteria for categorizing our exercise intensity spectrum. 

What fuels does our body use?

Your body typically burns a mixture of fats and carbohydrates during exercise to release the energy required (i.e. calories) for movement. Fat is a fuel source that releases more energy than carbs when burnt (i.e. 9 kcal per gram of fat vs 4 kcal per gram of carbs) but has a slower burning process making it suitable for low exercise intensities where the rate of energy demand is low. Carbohydrates on the contrary are a fuel source that requires less time to be burnt and consequently can sustain higher exercise intensities where the rate of energy demand is higher. The breakdown between 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.

Since measuring your oxygen consumption and carbon dioxide production by analyzing your breath requires you to wear a mask, the information of your body’s fuel breakdown becomes applicable in everyday training through the use of proxy metrics such as heart rate. Given that the relationship between your body’s fuel usage and your heart rate remains fairly constant one can measure heart during a metabolic test, establish the correlation between heart rate and fat-carbohydrate balance, and subsequently use only heart rate to approximate his fuel usage during training.

It’s important to note however 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. 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

How many training zones do we use? What benefits does each one bring?

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

Zone 2

Zone 2 training will develop your mitochondrial function and improve your fat-burning efficiency. It’s highly recommended for long-range endurance sports as well as individuals suffering from metabolic syndrome (e.g. Type II Diabetes). The improved mitochondrial function will also significantly support recovery capacity helping you to recover faster after intense bouts of exercise. 

Zone 3

Zone 3 training can help strengthen your pulmonary 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. A problem in the heart or lungs may be due to a disease or lack of training. 

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. Anaerobic metabolism is the energy generation process your body gradually initiates as exercise intensity increases. It has a high energy output capability and hence it’s the predominant energy generation process during high-intensity exercise but also creates bioproducts that cause fatigue. For as long as your body can clear these fatigue byproducts faster than their being produced the exercise intensity remains sustainable. The greater your lactate shuttling capability, the more you are able to clear these fatigue byproducts and the greater your ability is in sustaining high exercise intensities for long periods. 

Zone 5  

Zone 5 training will help improve your VO2max and peak power output capability (e.g. maximum speed or cycling wattage). This is an exercise intensity that’s sustainable for 60 to 120 seconds and requires one to train at his maximum potential.

Zone systems with more than 5 stages are harder to follow during everyday training because it’s typically impossible to maintain your heart rate in very narrow boundaries during real training conditions. Moreover, the differences in metabolic states between such narrow zones are non-significant which limits their added value in training limited.

Why should I care about training zones?

As we discussed in our article “What’s keeping you from achieving your fitness goal” every person, irrespective of age, gender, and fitness level has one or more systems in his body that are posing a limitation, in other words, are an obstacle to their fitness goal. Targeting these limitations effectively requires the precision that stems from focusing your cardio and interval training to the zone(s) that will inflict the adaptations needed to overcome your limitations.

The PNOĒ metabolic analyzer provides gold-standard accuracy in determining your training zones along with the plan that puts them to effective use. Understanding how your body responds metabolically and building your program based on that knowledge is a foundational step towards maximizing your workouts. You will be able to achieve your health or performance goals faster and with less effort.