Debbie Potts Coaching

The importance of training zones for health and performance

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Key points

  • Training zones are your heart’s response to the energy generation process as the workout intensity increases
  • Metabolic particularities differentiate the training zones per person
  • Training zones change over time depending on the type of training and nutrition programming one’s follows, so they need period reevaluation to remain relatable
  • The metabolic analysis is the gold standard in personalizing training zones and the plan to overcome limitations.

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. Training zones can significantly enhance the results one gets from cardio and interval training regardless of whether they are looking to break and triathlon record, get healthier or lose weight. As a result, they should be top of mind for everyone with a fitness routine.

This blog explains what training zones are, how they are determined, the effects each one has on human physiology, and how they can be used to inform training and nutrition better.

Exercise intensity zones and metabolic response

The human body has a different metabolic response depending on the exercise intensity it’s exposed to. Its metabolic response is defined based on the amount of energy (i.e. calories) and type of fuel (i.e. proportion of fats and carbohydrates) it uses at each particular intensity. For example in zone 2 one may be burning 4.5 kcal/min with a fuel mixture consisting of 75% fats and 25% carbohydrates. These attributes will gradually change as one moves to a higher level of exercise intensity zones because the energy demand increases, and the fuel mixture required to sustain the growing levels of energy release needs to change. To better understand this phenomenon we should first examine the process of energy generation in the human body.

During exercise, your body typically burns a mixture of fats and carbohydrates to release the energy required (i.e., calories) to move. This process typically uses oxygen and is thus also referred to as the oxidation of fats and carbohydrates. Fat 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, require less time to burn and can therefore support higher exercise intensities where the rate of energy demand is larger.

As a result, the fuel mixture changes from predominantly fats when exercise intensities and energy requirements are low to carbohydrates dominant as exercise intensity increases and the rate with which the body needs to release energy increases. In short, as the demand for energy increases, cells need to rely more on carbohydrates since they release energy faster. On the other hand, cells rely on fat as a fuel source despite its slow energy release process for as long as energy demand remains low.

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

Going from intensity zones to heart rate zones

As described above, exercise intensity zones are defined based on the body’s metabolic response when exercising at a specific intensity. The metabolic response is broadly defined by the calories expended and the contribution of fats and carbohydrates in the calorie-burning process at that particular intensity. To measure calorie expenditure along with fat and carbohydrate consumption, one needs to analyze an individual’s expired oxygen and carbon dioxide using a metabolic analyzer. Since metabolic testing can only be done in a test or evaluation setup and not on every training session or athletic event, one needs to use a proxy metric that can be easily tracked daily to map a person’s metabolic response against it. The most commonly used proxy metric to achieve this is heart rate.

By measuring heart rate during a metabolic test, we can establish a correlation between the different metabolic states the test subject undergoes and heart rate. Since this correlation remains fairly constant, once established, it can be used to infer the subject’s metabolic response just by tracking heart rate during training or athletic events. We refer to this as “getting your personalized training zones.”

How different are my heart rate zones from the person sitting next to me?

The answer is Very! There are many ways to estimate heart rate zones, including predictive equations and wearable devices. However, the metabolic particularities of an individual render these methods highly inaccurate, with some cases reaching up to 50% deviation from one’s training zones. Simply put, unless one uses metabolic analysis to evaluate metabolic response in conjunction with heart rate, it’s impossible to identify their true heart rate zones accurately.


Do training zones change over time?

Yes! Training and nutrition will impact the way your cells work and consequently will affect your metabolism. In broad terms, this means that you will burn a different number of calories and use a different mixture of fat and carbohydrates at specific exercise intensities. For example, after three months of endurance training, you have likely become more economical in your running. You now burn fewer calories at a given pace and perhaps more fat adapted, meaning that the proportion of fat metabolism in your energy generation process has grown. Since heart rate zones correlate between heart rate and metabolic response, if your metabolism changes, so will its correlation with your heart rate profile. As a result, depending on how rapidly you progress through your fitness journey or training, you should re-assess your training zones. The recommended testing frequencies are the following:

  • Every six months for individuals in a static or maintenance routine
  • Every three months, individuals progress through their fitness program at an average pace
  • Every 4-8 weeks, athletes undergo rigorous training

Moreover, it’s also very important to highlight that training zones also change based on the type of exercise. This is due to the fact that the amount of calories, fats, and carbohydrates you burn are heavily affected by the movement your body conducts. This inevitably means that the correlation between your metabolic response and heart rate profile will change depending on the 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. This may also explain why you feel a burning sensation in your legs when biking at a relatively low heart rate range while feeling much more relaxed when running at the same heart rate.

Training zones and physiological adaptations

Each training zone elicits different physiological adaptations on the human body. These physiological adaptations include improved cellular fitness, heart fitness, lung capacity, VO2max, and more. Each zone has specific effects meaning that spending time in it will improve only a specific set of these systems and not everyone. As a result, when one is looking to get the most out of their cardio training by targeting specific weaknesses their body faces, following a training program with accurate training zones is essential. For example, spending a specific period in zone 2 is the essential part of a training program if one is looking to improve their fat burning efficiency. If this person hasn’t measured their personalized training zones and instead of training in Zone 2 they’re actually training in Zone 3; they may be getting as much as 40% less positive adaptation in enhancing their fat burning capacity.

The five zones system is the most frequently used one, accurately capturing 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. Here are the adaptations each zone will affect:

Zone 1
Training intensity is typically used for warmup or active recovery (i.e. recovering from intense exercise while moving).

Zone 2
Zone2 raining will develop your mitochondrial function and improve your fat-burning efficiency. It’s highly recommended for long-range endurance sports and 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 solid 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 also be used as fuel by your muscles. For as long as your body can clear fatigue byproducts faster than their being produced, the exercise intensity remains sustainable. As a result, the greater your lactate shuttling capability the greater your ability to sustain high exercise intensities for long periods.

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 full potential.

Key takeaways

Regardless of age, gender, and fitness level, every person has one or more systems that limit fitness or health. Targeting these limitations effectively requires the precision that stems from focusing your cardio and interval training in the zone(s) that will bring about the adaptations needed to overcome them.

The metabolic analysis provides gold-standard accuracy in determining your training zones and the plan that puts them to effective use. Understanding how your body responds metabolically and building your program around your metabolism is a foundational step toward maximizing your workout’s efficiency and achieving your health or performance goals faster and with less effort.

PNOE: The benefits of a well-rounded individualized exercise program and the importance of testing.

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Key points

  • Achieving someone’s goals requires an individualized exercise program that will combine all three exercise modalities, namely resistance, cardio, and interval training.
  • VO2max testing is the gold standard for individualized exercise prescription based on tailored training zones.
  • All people, irrespective of their fitness level, may be eligible for all types of exercise, with the adequate adaptations that will allow for progressive overload.

Exercise not only maintains physical and psychological health but also helps our bodies respond to the negative consequences of several diseases, such as diabetes, hypertension, and cardiovascular disease. Exercise is also a valuable adjunct to diet for people trying to lose weight and, in general, combat overweight and obesity. However, most people opt for the most effortless methods of diet (a few days of fasting, detox diets) and exercise (electrical muscle stimulation, body therapies) because they do not want to bother that much. Such an approach mostly leads to the opposite outcomes because they are not fruitful, cause frustration, and eventually impede any weight management endeavor even more.

Exercise as an integral part of weight management

In a previous Blogpost about weight management in terms of weight loss and maintenance, we focused on energy balance and the fundamental pillars of a sustainable weight loss program, one of them being exercise. It was acknowledged that although energy restriction is the most vital part of the weight loss process, exercise can have additional benefits when combined with an adequate calorie deficit.

In particular, weight loss efforts are typically subsumed under the adaptive biological mechanisms that forcefully fight against them. As a result, these mechanisms sooner or later lead to weight loss plateau and subsequently weight regain. This is where exercise could act as the lifeline to attenuate these devastating effects.

Most health organizations have highlighted the importance of exercise. Specifically, the American Heart Association (AHA), for disease prevention, improved quality of life, and overall health and well-being, recommends that we get at least 150 minutes per week of moderate-intensity aerobic activity or 75 minutes per week of vigorous-intensity aerobic activity, or a combination of both in combination with resistance training on at least two days per week.

However, these recommendations are pretty generic. Someone who enters a weight loss program should remember that to achieve their goals, they should aim for an individualized exercise program from an exercise specialist that will combine all three exercise modalities.

Training zones

Three distinct types of exercise can all be valuable tools for a dieter’s quiver. Therefore, all should be involved in the appropriate amounts in an individualized exercise regime for weight loss. These are a) Resistance training, b) Cardio training, and c) Interval training.

Resistance training involves exercises designed to improve muscular strength, endurance, and muscle size.

Cardio training is any cardiovascular exercise that will increase your breathing and heart rate and involves using oxygen for energy supply to the working muscles.

Interval training involves alternating short high-intensity aerobic exercise bouts interspersed with low-intensity or rest recovery periods.

Cardio and interval training are governed by some training principles, which are reduced to the training zones.

The gold standard method to determine someone’s training zones is implementing cardiopulmonary exercise testing (CPET), also known as VO2max testing. VO2max is the maximal rate of oxygen uptake during exercise. It is the gold standard for individualized exercise prescription. The training zones determined through such an approach are five and are described based on two variables; the maximum heart rate (HRmax) during a VO2max testing or the anaerobic threshold (VT2). VT2 is where during VO2max testing, your body must switch from aerobic to anaerobic metabolism for energy supply.

VT2 differs from VT1 (ventilatory threshold), which can also be determined through VO2max testing and refers to the point during exercise where ventilation increases faster than oxygen uptake.

The training zones are described as follows:

  • Zone 1 (recovery/easy): 55%-65% of HRmax or 75%-80% of HR at VT2. This zone is used to get your body moving with minimal exertion. It may be appropriate for an easy training day, warm-up, and cool-down.
  • Zone 2 (aerobic/base): 65%-75% of HRmax or 81%-89% of HR at VT2. This zone is used for longer training sessions, such as endurance sports. Subjects working in this zone can improve their mitochondrial function and fat-burning efficiency.
  • Zone 3 (tempo): 80%-85% of HRmax or 96%-100% of HR at VT2. This zone can be used to build up speed and strength. It can also be appropriate for people who suffer cardiopulmonary limitations since it can help them strengthen their pulmonary muscles and improve their cardiovascular system.
  • Zone 4 (anaerobic threshold): 85%-88% of HRmax or 102%-105% of HR at VT2. This is the zone where lactic acid, as a by-product of the anaerobic metabolism, builds up, and thus fatigue kicks in. Training in this zone helps your body improve its VO2max and efficiency when working at its maximum sustainable pace.
  • Zone 5 (aerobic-anaerobic): 90% plus of HRmax or 106% plus of HR at VT2. This zone can only be maintained for a minimal time (60-120 seconds). It can improve your VO2max, your peak power output capability (e.g., maximum speed or wattage), and increase your fatigue threshold at maximum intensities.

As demonstrated above, each training zone elicits different physiological adaptations to the human body, and training zones may vary significantly from person to person. This is why it is strongly recommended that zones be determined through VO2max testing and not using predictive values.

Exercise modalities in a nutshell

a) Resistance exercise

It’s a form of exercise that increases muscular strength and endurance by exercising a muscle or a muscle group against external resistance. This external resistance might be resistance bands of different weights, dumbbells, machines, barbells, kettlebells, and even bodyweight.

Different adaptations associated with a resistance training program include muscular endurance, muscle size (hypertrophy), and strength (explosive training). All types of resistance training contribute to muscle mass increase and enhanced metabolism since muscle mass is the primary metabolically active tissue. Each of these adaptations is characterized by a group of variables, namely the number of sets, the number of reps, tempo, time of rest, and intensity (in terms of 1RM).

Anyone at any fitness level can perform resistance training. It’s all about finding the right exercise variations and the proper resistance that will allow you to progressively overload and complete all reps with good form. However, compared to a muscular endurance program, the number of sets and the intensity increases, whereas the number of reps decreases for the hypertrophy and maximum strength phases of a resistance training program.

Maximum strength/Explosive training can significantly improve VO2max, power output at VT1 and VT2, and movement economy, namely an enhanced caloric burn during low-level movements (NEAT). It can also increase the fatigue threshold at maximum intensities and improve the rate of force development, namely, an athlete’s explosive strength.

On the other hand, hypertrophy training can significantly increase muscle size and enhance force development. However, it can reduce VO2max and the formation and development of blood vessels in the muscles trained.

Muscular endurance training can significantly improve VO2max and power output at VT1 and VT2.

Irrespective of each different type described above, resistance training can increase bone density and boost metabolism through increased muscle mass, which is the primary metabolically active tissue in the body. A well-rounded resistance training program could encompass all its different adaptations in separate exercise sessions, depending on the subject’s training goals and the restraints identified through VO2max testing.

b) Cardio training

Cardio training, also known as aerobic endurance training, is the most basic form of exercise since it can be as simple as walking. It is a continuous steady state exercise that can contribute to building cardiovascular endurance and weight loss when used wisely and not excessively. It is the main form of exercise recommended by the American Heart Association (AHA) for overall health and well-being.

Cardio training can further be categorized into base-long, base-medium, moderate, and heavy continuous, based on the %HRmax intensity of the exercise.

  • Base-long cardio training or zone 2 (65%-75% HRmax) may last 120-240 minutes and can improve movement economy and fat-burning efficiency. It can also secondarily enhance the speed at VT1 and lower the heart rate at submaximal intensities over time.
  • Base-medium cardio training between zone 2 and zone 3 (70%-79% HRmax) may last 60-120 minutes and can significantly improve the speed at VT1 and lower the heart rate at submaximal intensities over time. It can also secondarily enhance movement economy and fat-burning efficiency.
  • Moderate cardio training or zone 3 cardio training (80%-85% HRmax) may last 40-60 minutes and will chiefly improve the speed at VT2. It can also secondarily enhance movement economy, fat-burning efficiency, and speed at VT1.
  • Heavy continuous cardio training or zone 4 cardio training (85%-90% HRmax) may last 20-40 minutes and can significantly improve the speed at VT2 and VO2max.

Cardio training is the simplest form of exercise and can be used by anyone, irrespective of their fitness level and medical history. Deconditioned people and/or those with cardiorespiratory limitations should start at lower cardio training intensities (base-long and base-medium) and progressively move to more intense cardio training workouts. However, it should be noted that all categories of cardio training may be useful for different training goals that a subject may have. Therefore, they can coexist in a cardio training program.

c) Interval training

Interval training involves repeated workout periods (intervals) at an intensity between 83%-100% of your maximum heart rate. In terms of training zones, such intensities correspond to zone 4 and zone 5. It can further be categorized into short, medium, and long based on the duration of each interval.

  • Short interval training encompasses 10 seconds to 1-minute intervals and may last 8-12 minutes in total. It can mainly improve VO2max.
  • Medium interval training encompasses 1- to 4-minute intervals and may last 12-24 minutes. It can mainly improve VO2max and, secondarily, the speed at VT2.
  • Long interval training encompasses 4-minute to 10-minute intervals and may last 20-30 minutes. It can significantly improve VO2max.

Short interval training is highly mechanically demanding and is recommended to be mainly performed by well-trained subjects. Medium and long interval training is also aimed at subjects with lower fitness levels. A less trained subject may start with the lower time limits and progressively reach 10 and 4 minutes, respectively.

Interval training can either involve a single exercise, i.e., running on a treadmill or biking or rowing, or multiple activities of different levels of difficulty, i.e., free or lightly-to-moderately weighted squats + lifts with an empty barbell or lifts with a lightly or moderately loaded barbell + jumping ropes, etc. All these parameters are determined by the subject’s goals, fitness level, and potential limitations identified in the VO2max exercise testing.

HIIT training, like cardio training, is considered a cardiovascular exercise where subjects can improve their cardiovascular and respiratory function and lose fat. Its main advantage compared to cardio training is that it can be completed in a maximum of 30 minutes, including the warm-up. In other words, it can save a considerable amount of time for those whose argument for not working out regularly is the time constraints.

Interval training can essentially be used by anyone who wishes to reap the benefits of this type of exercise. However, for severely deconditioned subjects who at the same time suffer metabolic, cardiovascular, and/or respiratory limitations and their doctor has advised them not to participate in vigorous exercise, it’s more prudent that they embark on base-long and base-medium cardio training, namely low-moderate intensity cardio training first, and gradually proceed with more intense interval workouts.

Cardiopulmonary exercise testing (CPET)

As stated above, the gold standard for exercise prescription is CPET. It should be performed by anyone who wishes to enter a congruous exercise program and achieve their weight loss and/or training goals as efficiently as possible.

Generally speaking, a well-rounded exercise program should involve all three exercise modalities since they serve different training goals and result in various training adaptations. However, CPET can precisely determine the level of exercise performance of the subject that undertakes it through the combination of multiple variables, including ventilatory, musculoskeletal, cardiovascular, and metabolic characteristics. Based on those, it can provide a tailored exercise prescription with a specific workout breakdown and define contraindications to an exercise program.

For example, the exercise prescription will promote hypertrophy training if someone has a low metabolism. If cardiovascular limitations (e.g., low VO2max) are found, the exercise prescription will promote long intervals and base-long cardio training. The exercise prescription will promote base-medium cardio training if low movement economy and/or low-fat burning efficiency are found.

Key takeaways
Exercise can help people struggling with weight loss plateau and tend always to regain the lost weight, accomplished through diet programs alone.
All three types of exercise, i.e., resistance training, cardio training, and interval training, should be involved in an individualized exercise regime for weight loss.
The amounts for each exercise modality should ideally be determined through cardiopulmonary exercise testing, which is the gold standard for exercise prescription. The exercise prescription should not only be in line with the person’s exercise and weight goals but also with their limitations, which are distinctly defined through CPET.

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