Deciphering the enigma of intensity zones and the concept of risk management
An article written by Sophie Herzog, Øyvind Sandbakk, Trond Nystad and Rune Talsnes
Discussing, executing and analyzing training can often feel frustrating due to the lack of standardized intensity zones definitions and the absence of a universal approach to their application in training. The diversity is evident across countries, regions, sports and even coaches, who all seem to develop and implement their own terminology and definitions for intensity zones. This inconsistency extends to the scientific literature, where various expressions, definitions, and measurement methods further muddle the waters. Consequently, comparing different studies, aligning scientific findings with practical training and evaluating different training methods and philosophies across sports and cultures becomes challenging.
The search for a universal definition that is perfectly applicable to every athlete and every sport is like chasing the impossible – each definition has its strengths and weaknesses. Nevertheless, it is important to establish a consensus on basic definitions and cultivate a common understanding of the terminology. Achieving this foundational agreement will pave the way for meaningful discussions about the application of intensity zones, the associated measures of intensity and the distribution of intensity in training across different sports and individual athletes[i].
Developing a shared language
Using the same language, i.e., having shared definitions, understandings of intensity zones and mental models, ultimately helps us plan, execute, analyze and compare training with better quality[ii]. An intensity-zone system we know well and find helpful is the one created by the Olympic federation in Norway (Olympiatoppen). It describes five intensity zones for aerobic endurance training[iii] (zone 1 to 5, see Table 1), in addition to three anaerobic zones (zone 6 to 8). This system may not be perfect, but it has scientific roots in physiological threshold-definitions and is a universal framework used by coaches and athletes across endurance sports in Norway. This is beneficial when planning, monitoring, executing, documenting, analyzing and comparing training within and across sports, and when implementing new scientific findings.
Table 1: Summary of aerobic intensity zones for Norwegian Olympic Sports (In Norwegian: https://olt-skala.nif.no/#ventilasjon_m). These tables were developed in consultation with the respective sports associations and can be adapted to different sports and to different individuals.
But why do we need (intensity) zones in the first place and why are they so difficult to delineate? Different zones are used to describe what happens physiologically or what adaptation is targeted through training interventions. By training in different zones, athletes and coaches can enhance various aspects of performance such as endurance, speed and recovery. Hence, each zone is thought to correlate with distinct changes in heart rate, perceived exertion, muscle fiber recruitment, energy substrate utilization, breathing, lactate metabolism, etcetera.
On a very basic level we can compare intensity zones with speed limits when driving a car. Traffic is regulated with maximum speed limits, and in training we also use a variety of parameters to regulate and control the intensity. The difference between going 30 km/h versus 300 km/h in a car is easy to see and feel, but the difference between 40 and 50 km/h is very hard to see and feel, hence in a car we need a speedometer to measure the difference. In sports, this is similar. It is easy to see and feel the difference between sprinting as fast as possible and jogging slowly – the physiological differences are easily distinguishable: High-intensity work involves near-maximum heart rate, the use of both slow- and fast-twitch muscle fibers, anaerobic metabolism, high lactate production and high rate of perceived exertion (RPE). In contrast, an easy run involves low to moderate heart rate, predominantly slow-twitch muscle fibers, aerobic metabolism, minimal lactate production, and low RPE. However, in a 1-hour easy run (zone 1) versus a 1-hour moderate run (zone 2), the differences are more subtle and harder to distinguish without precise measurement tools. Both involve primarily aerobic metabolism, but during the latter you probably have a slightly higher heart rate, breathing rate, and carbohydrate utilization compared to running “easy” (a prescription that has its intricacies too, as we will see later). The RPE is also slightly higher in zone 2. These subtle changes necessitate precise tools like heart rate monitors, lactate testing, and careful subjective monitoring to accurately differentiate and target specific training adaptations.
Furthermore, the duration of each session naturally influences the intensity of the session. For example, zone 1 sessions are by nature far longer than zone 5 intensity sessions. In addition, it is important that athletes execute the session in alignment with the goal of the session. For example, if the coach and athlete aim to perform a zone 3 session, then the athlete should execute and document a zone 3 session. In other words, planning and execution are coinciding and the objective and subjective parameters are in line with the plan. In Table 2 you see examples of typical sessions for each zone for an adult endurance athlete.
Table 2: Session examples and prescriptions using the five-zone model used in Norway.
Intensity zone systems, such as the one used by Olympiatoppen, include various intensity measures or reference points which can help us determine what intensity we are using or aiming for in training (see Table 1). Some of these factors are internal (e.g., lactate, heart rate, ratings of perception, etc.) and some external (e.g., speed, power, etc.) measures of intensity, some are objective and thus dependent on accurate and consistent measurements, and some are subjective and thus reliant on a good understanding and feeling for the body. It is clear from the diversity of these measures, that an oversimplified or reductionist approach to prescribe training (e.g., considering one parameter as much more important than all others) is not appropriate. To illustrate how difficult it is to de- or prescribe training based on a single parameter, we can think about how people understand and implement a word like “easy”. The execution of an “easy” session will vary greatly based on experience, perception, and culture. An example from the world outside of sports perhaps makes it even clearer: if someone tells you it is “warm”, then this word has a completely different meaning if referring to “warm” on top of Mount Everest or “warm” in the Sahara. Deciphering the meaning is dependent on the context, which applies even to the more “exact” and objective measures. Again, the meaning of these parameters depends on the context or background information about the athlete. For example, if we use a percentage of maximal heart rate as a prescription for intensity, we must know the exact maximal heart rate of the athlete in this modality (i.e. running, cycling, swimming). This is not always feasible because one might lack appropriate tests or measuring tools. In addition, it is important to consider the measurement method. To stay with the example of heart rate: Does the athlete use a heart rate monitor (chest strap), or does he/she use the wrist measurement of so-called smartwatches, which are (as of yet) far less accurate? Lastly, intensity descriptions based on internal parameters such as heart rate or lactate are very individual and can vary from day to day. Not all athletes have their thresholds at the same absolute lactate values as previously assumed by Mader et al.[iv]. Some produce less lactate and others more, which is easy to explain from a physiological point of view. For example, athletes with large blood volumes and a high proportion of slow twitch fibers (producing little lactate) will give lower lactate concentration in the blood than athletes with lower blood volumes and more fast-twitch fibers. Still, many still do not take such inter- and intra-individual variations into account.
So finally, whilst the definitions by Olympiatoppen are not super strict and leave room for individualization, it is important to have these reference values as a starting point to develop a good understanding of intensity. It is part of the maturation and development process of an athlete to experiment with different intensity measures and tools in order to “calibrate” their own intensity control system. However, it should be noted that this “calibration” is not definitive. Many of the values in Table 1 are not only depending on the individual but are also highly dependent on training condition, nutrition/ hydration status, altitude, environmental factors (heat/cold/weather), terrain (flat/hilly), surface, modality, technique, equipment and many other factors. It is for instance possible for a highly trained cyclist to have 1 mmol/l in blood lactate with a heart rate of 150 beats per minute when biking but getting a lactate value of >3 mmol/l with the same heart rate when running. This does not only reflect the training status of this athlete in a specific modality but also that “easy” from one reference point (here, lactate), does not necessarily mean “easy” from a muscular or cardiorespiratory standpoint. The intensity puzzle is complex. However, with experience, athletes and responsible coaches should be able to differentiate between the different intensity zones based on heart rate, feeling, rate of perceived exertion, lactate, respiration, etc. and be able to implement, document and communicate the intensity correctly.
Marrying intensity prescription with risk management
In addition to gaining a comprehensive understanding of intensity (zones), it is also important to understand and mitigate risks in training. To ensure athletic development, we need to find a good mix of training at different intensities, plan and execute our training well and understand the associated costs and benefits. Therefore, we would like to introduce the concept of risk management in training. In the world of finance, the balance between risk and reward is well known: High-risk investments can lead to a high reward or a total loss, low-risk investments can lead to marginal but compounding returns or even a high return. This is very similar in training (planning) - the best investments are those where the risk is close to zero and the return (small to large) is guaranteed, a “safe bet”. This assures continuity in the training process, and over longer timeframes the consistent improvements will have major effects. This compound effect is a strategy that can turn small, seemingly insignificant actions into large gains. Let’s look at a few examples of risk taking in training:
A high risk, low/no return would be if you train when sick or injured. A high risk with a potentially high return would be to increase the number of intensity sessions over a short time frame (e.g., double threshold days). In this case very accurate intensity control is the key to reduce the risk. But what we are aiming for are low risk scenarios with a high likelihood of a consistent reward. For example, training at lower intensity on longer sessions, better nutrition before/during/after training, paying attention to recovery, reasonable increase in volume and intensity, listening carefully to body signals and rather skipping a session if in doubt, applying testing and monitoring, sleeping more, working on technique, planning, etc… The list goes on and on. When evaluating risks in training (planning), it is important to involve the athlete in all aspects and assess where the most gains can be made by taking the least number of risks (“best bang for the buck”).
Risk Management Matrix
Table 3: A systematic analysis of “risk” and “reward” is needed to plan, prioritize and execute training. The color scheme might vary a little from person to person, but the idea is to use a system to operate more in the “dark green” area and do less of the activities which fall into the “red” area.
Risk management is a concept which must be understood and implemented by every coach and athlete. Like in a strategy game, the idea is to stay mostly in the “dark green” area (see Table 3) and avoid staying in the “red”. The amount of “red”, or the level of risk one is willing to take depends on a lot of factors, including timing of the decision. Sometimes you have to go “all-in” and take a high-risk decision with the potential of a high return, and sometimes there are better solutions that expose the athlete to less risk and are more sustainable in their long-term development. One athlete we have worked with found himself in a situation where the body did not work anymore and the results were far from what was expected[v]. When analyzing the training we saw that this athlete’s program contained many high-risk elements: a focus on twice-per-day high intensity sessions, poor intensity control and long sessions with no carbohydrates. After a thorough analysis, we decided to change training in the opposite direction, towards the “green”, quadrant. This meant less training volume (in the beginning, followed by a steady increase), fewer hard sessions (more zone 3 instead of zone 4/5), intensity control on all sessions, 60-90 grams of carbohydrates per hour during training and more carbohydrates before and after training, as well as close monitoring and testing. His “new” training system involved much less risk, which in the end turned out to be the year where the athlete could train the most, which allowed the athlete to perform better and return to a world class performance level. In other words, the lower risk enabled more continuity, a long-term accumulation of more training and thus continuous development.
To summarize, we need to develop a shared understanding and definitions of intensity to ensure that we can plan, implement, analyze and discuss training. Furthermore, we must recognize the “costs” associated with high-risk elements in a performance system. While we presented the framework of the elite Norwegian sports system (Olympiatoppen) to exemplify the importance of a universal language, you do not have to use the same definitions presented in this document. However, regardless of which system and definitions you use, you must ensure that everyone involved has a clear and shared understanding. In subsequent blog posts we will discuss the application of different intensities, how you can use them to make a training plan and how they influence athlete development. If you need individual support in intensity management or want to go more in depth about training and intensities, please get in touch, set up an appointment or subscribe to our educational programs.
[i] Seiler, S & Tønnessen, E. Intervals, Thresholds, and Long Slow Distance: The Role of Intensity and Duration in Endurance Training. SPORTSCIENCE · sportsci.org. 2010;13. 32- 53.
[ii] Bucher Sandbakk S, Walther J, Solli GS, Tønnessen E, Haugen T. Training Quality-What Is It and How Can We Improve It? Int J Sports Physiol Perform. 2023 Mar 25;18(5):557-560. doi: 10.1123/ijspp.2022-0484. PMID: 36965489.
[iii] Olympiatoppen’s intensity scale: https://olympiatoppen.no/fagomrader/utholdenhet/olympiatoppens-intensitetsskala/ (June 2024)
[iv] Mader A, et al. Zur Beurteilung Der Sportartspezifischen Ausdauerleistungsfähigkeit Im Labor. Sportarzt Und Sportmedizin. 1976;27(4):80–8.
[v] Talsnes RK, Moxnes EF, Nystad T, Sandbakk Ø. The return from underperformance to sustainable world-class level: A case study of a male cross-country skier. Front Physiol. 2023 Jan 9;13:1089867. doi: 10.3389/fphys.2022.1089867. PMID: 36699686; PMCID: PMC9870290.
