Over these years working as the head of the athletic training section at Undertraining, I have often had to answer various questions from athletes (both amateur and professional) who, tired of cycling or running randomly, following only their feelings and without having actual feedback, have sought our advice to improve their aerobic performance.
The major doubts can be summarized as follows:
- How can I know and monitor the correct intensity of effort during training?
- What does it mean when my training partner says that they conducted a session in target zone number 2?
- What type of fuel is the metabolism using at these speeds?
The solution that provides an answer to these questions is only one: using a heart rate monitor and leveraging the different heart rate zones!
Heart Rate
Thanks to improvements in lifestyle, in recent years there has been an increase in the number of amateur athletes. To help those who are taking their first steps in basic physical activity, simple charts have been developed.
Are you aware that on heart rate monitors from major sports brands such as Polar, Suunto, Garmin, TomTom, Adidas, Nike, Reebok, etc., the percentages of heart rate are divided into 5 or 6 percentage ranges?
These intervals (also called “target zones”) indicate to the athlete what type of effort they are exerting, i.e., what metabolism is supporting the physical effort, what type of fuel is being used, so they can easily and quickly calibrate the training stimulus.
To improve sports performance, you must train every time to the maximum of your capabilities, using work intensities that do not waste your time (because they are too mild) and, on the other hand, do not put you at risk of injury (because they are too intense).
The simplest and at the same time most practical parameter to use during your workouts is the heart rate.
The number of beats per minute (bpm, or “beats-per-minute”) maintained for a certain period of time will help you monitor if you are respecting the correct work intensity and how the heart is managing the effort.
But how do you evaluate this data, which is so personal and therefore different from individual to individual?
What information should I enter into the application that manages the heart rate monitor so that it provides an answer as close to reality as possible?
To organize your outings, we only need to know two heart rate parameters: resting heart rate and maximum heart rate.
The values for resting heart rate in a healthy adult range from 60 to 80 beats per minute. They correspond to the minimum number of myocardial beats under conditions of relaxation. For an accurate assessment, you should measure it in a calm state: the best time is therefore in the morning, after you have gotten out of bed and have sat for a few minutes.
The maximum heart rate, however, is the maximum number of beats per minute that the body can tolerate. Its identification is not simple, considering that it varies a lot from person to person. Lifestyle, consistency in sports activity (occasional or frequent), the presence of aerobic sessions in one’s training, possible congenital predispositions, are some variables that can influence this data.
In the case of deconditioned individuals, conducting a test that allows the detection of the maximum frequency at which the heart can beat could be prohibitive, in addition to posing serious risks.
In these circumstances, theory comes to our aid.
Through formulas based on extensive statistics, it is possible to determine the maximum heart rate, and hence the different percentages of effort, with sufficient accuracy.
Let’s quickly list the most commonly used formulas.
The first formula I propose is the simplest but also the least precise: Cooper’s formula.
Max HR = 220 – age
The second is Tanaka’s formula, slightly more complex, but much more accurate.
Max HR = 208 – (0.7 x age)
The third is the one that has proven to be the most accurate to date, that of Sally Edwards.
Max HR for men = 210 – (age/2) – (0.11 x weight in kg) + 4
Max HR for women = 210 – (age/2) – (0.11 x weight in kg)
Now that you know the correct figures to input as limits in the tool that monitors your beats, you have increased the precision with which you control this parameter, and you will thus be able to answer questions like:
- At this moment in my training, am I in the aerobic phase or the anaerobic phase?
- Based on the goal of the session, should I decrease or increase the intensity of pedaling or running?
- According to the heart rate monitor, am I in the correct intensity zone?
Now, back to the intensity zones.
Let’s briefly delve into this table (for convenience, I describe 5 target zones, as you would find in the most common applications of major brands) by adding some additional data, to explain how each heart rate segment corresponds to a specific stimulus.
Zone 1
As soon as you start moving, you find yourself in a low-intensity work zone, which corresponds to aerobic endurance.
The heart rate is between 50 and 60% of max HR.
The effort is mild, you’re relaxed; in this phase, the body burns a minimal amount of fats through the aerobic energy system.
The term “aerobic endurance” refers to basic endurance, which is the process of improving the physical characteristics that form the foundation of endurance performance, thus affecting cardiac and respiratory efficiency, energy metabolism, and capillarization (the increase of blood vessels in muscles corresponding to greater oxygenation of tissues).
The training that allows this type of improvement involves long-duration activities at low intensity.
Zone 2
You’ve slightly increased the intensity of your run or bike ride; you’re now in the zone of aerobic capacity, which is the quantitative aspect of performance, broadly identifying your level of endurance.
The heart rate is between 60 and 70% of max HR.
When your heart rate monitor shows this range of beats, it means you’re facing a clear effort, but you’re still relaxed, not perceiving it as too strenuous. Although your breathing becomes a bit shorter, you can still exchange a few sentences with your training partner.
You are fully in the aerobic phase and are primarily burning fats; there is minimal production of lactic acid, which your body can quickly dispose of, thus avoiding its accumulation.
To maintain this level of performance without difficulty, you will need to be able to handle slightly faster paces compared to those used in Zone 1, for a substantial number of minutes. It will therefore be essential to include in your training program medium-paced outings and progression work (i.e., dividing the session into three units: a slow first part, a medium second part, and a final part that is much more pushed).
The outings will always be fairly long, but the speed of running or pedaling will be clearly higher compared to Zone 1: this way, you will have improved the efficiency of the muscles in using oxygen and fatty acids.
Zone 3
You are at the limit of the pure aerobic mechanism, in the zone of aerobic power.
The heart rate is between 70 and 80% of max HR.
Breathing starts to become labored, you can only speak a few words, the effort is noticeable. The fuel that your muscles are predominantly using is carbohydrates (glycogen), as the glucidic aerobic energy system is in action.
In addition to allowing the maintenance of more sustained speeds compared to aerobic capacity, the development of aerobic power improves the muscles’ ability to utilize the available oxygen even better and to work even in the presence of small amounts of lactic acid. This can happen if, through the training performed in the two zones just described, you have meanwhile increased the mitochondrial density within the muscle fibers, that is, if you have increased the number of mitochondria (the organelles within the cell that act as power plants: using oxygen to dispose of lactate and produce new energy).
In the period when you intend to develop aerobic power, it will be useful to include both short and fast workouts, in which you must maintain a constant running or pedaling pace, and workouts with interval intensity, thus with long repeats followed by stretches where you recover and dispose of the few millimoles of lactic acid that you have meanwhile produced.
Zone 4
Muscles begin to accumulate lactic acid: you are in the transition zone between the aerobic and anaerobic mechanisms, that is, in the anaerobic threshold zone.
The heart rate is between 80 and 90% of max HR.
If the heart rate monitor indicates that you are pedaling in this zone, it means that the body is working hard, the heart is under strain, and breathing is short.
The body is about to enter the anaerobic phase, where there is such a large production of lactic acid that the body struggles to dispose of it all, thereby causing accumulation, intoxication of the fibers, and a forced slowdown in performance.
A series of repeats over medium distances should not be missing in a training program that aims to improve you in this intensity zone.
[Side note: a beginner knows, thanks to this table, that their anaerobic threshold falls between 80 and 90% of max HR, but an athlete intending to participate in races needs to know precisely the transition line between aerobic and anaerobic energy systems. Their athletic performance is also based on this data. For a 35-year-old athlete, there is a significant difference between training at 82% of max HR (147bpm) and 89% of max HR (160bpm). Almost 15 beats per minute difference is no joke! This is why numerous protocols have been created for tests that are used to investigate at which heart rate the anaerobic threshold occurs.]
Zone 5
Now you are sustaining an intense effort despite the considerable presence of lactic acid. You have surpassed the anaerobic threshold, the muscle is filling with lactic acid, the fatigue is significant, and the speed is remarkable; from this point, the aerobic system is significantly supported by the anaerobic mechanism.
The heart rate is between 90 and 100% of max HR.
These pedaling intensities are not sustainable for long; you are expressing the maximum possible aerobic performance, the cardiovascular system is under enormous stress.
You have reached the maximum oxygen consumption, or VO2max.
Medium and short repeats are most suitable to help improve what is defined as anaerobic capacity.
Try to perform short repeats almost to the best of your ability, making sure you have fully recovered before tackling a new high-speed stretch.
If you do not want to, or cannot, pedal or run so fast, perhaps due to suboptimal road conditions, excessive traffic, or stiffness and fatigue in your muscles, you can use medium repeats, but with a small precaution!
Having decided to keep the speed slightly lower, my advice is then to play with the recovery times between repeats: try to shorten the time you take to catch your breath, in order not to give enough time for the lactic acid to be cleared from the muscle fibers that produced it.
You will force the muscle fibers to continue their work of contraction even in conditions of high local acidosis, thereby seeking progress in anaerobic capacity.
Zone 6 or Zone X
In addition to the 5 zones I just described, there is also a sixth zone.
What could possibly exist beyond 100% of the maximum heart rate?
The sixth zone has nothing to do with the aerobic system, which is why it does not appear in the charts.
However, I want to provide you with as complete a picture of the situation as possible.
This zone is important and should not be overlooked: it is always included in the training programs I recommend to the athletes I coach.
Anaerobic power allows the body to reach high speeds but only for limited periods of time, a few tens of seconds: for example, in athletics, it is used by sprinters or long jumpers.
To improve this characteristic, include in your training program very short high-speed repeats, allowing yourself ample recovery times, in order to allow the restoration of the phosphocreatine stores just used.
I emphasize again that this Zone X is not involved in the aerobic system, you will not find it on your heart rate monitor, but to complete the discussion on the metabolisms you can engage during training, it is right to write a few lines.
Conclusions
We have seen how the heart rate monitor is a valuable tool for optimally setting up training sessions.
For both a novice at their first encounter with physical activity and for a more experienced athlete, these tables can be a valuable aid in monitoring training and managing effort according to the goals set.
If you want more information, or to undergo a submaximal test that allows you to know your anaerobic threshold, or if you need help planning your sports season optimally, send an email to roberto@undertraining.ch to request your free consultation with Roberto.
Or request a free consultation with him by clicking the button below:
Luca Russo
Dr. in Sports Science
Personal Trainer, Athletic Trainer
