Low intensity training: The most important and most ignored training intensity for endurance athletes
An article written by Sophie Herzog, Øyvind Sandbakk, Trond Nystad and Rune Talsnes
Research on training intensity and its distribution in elite endurance athletes reveals a paradox: While most studies focus on High Intensity Training (HIT), corresponding to zones 4 to 5 in the Olympiatoppen (OLT) intensity zone model[1], retrospective studies on elite endurance athletes (see Figure 1) show that 70-90% of the total training volume is classified as low intensity training (LIT)[i],[ii],[iii],[iv], corresponding to zone 1 and 2 in the OLT model. This significant time accumulated as LIT allows athletes to build a robust “aerobic base”, even though the precise underlying mechanisms are not entirely understood.
Figure 1 shows an overview how the training intensity distribution looks like for world-class athletes in a variety of endurance sports[ii]. Please note that this study uses a 3-zone intensity model.[2]
Figure 1: The training-intensity distribution (i.e., percentage time spent in zone 1: below first ventilatory threshold or steady-state blood lactate concentration at 2 mmol/L; zone 2: at or near lactate threshold (~4 mmol/L) or second ventilatory threshold; zone 3: high-intensity training above lactate or second ventilatory threshold) in well-trained to elite endurance athletes in retrospective analyses during (A) preparation phase, (B) pre-competition phase. Adapted from Stöggl and Sperlich[ii].
It's essential to recognize that HIT, Moderate Intensity Training (MIT), and Low intensity Training (LIT) are not in competition with each other; rather, they are complementary components of a well-rounded training program. Intensive sessions in the form of MIT and HIT are universally regarded by elite coaches as fundamental key sessions to achieve performance progression. The planning and implementation of training routines are primarily centered around these key sessions. However, the quality and “absorption” of these high-intensity sessions relies heavily on the foundation provided by large volumes of LIT. For athletes to execute intensive sessions effectively and consistently, LIT must play a supportive and complementary role. Therefore, a prevalent opinion is that LIT sessions should be easy enough to ensure that the intensity sessions can be executed with intended quality. At the same time, LIT sessions are not recovery sessions and should have sufficient speed/power to allow good technical quality and provide sufficient load to obtain positive adaptations. Fundamental questions that need to be answered are therefore: How easy is easy enough? And what is too easy?
In most “intensity models”, the LIT zone covers a wide range. In the Olympiatoppen way of describing intensity[1], LIT entails zone 1 and 2 (see Figure 2), or a heart rate range from 60-82% of maximal heart rate (HRmax). If someone has a maximum heart rate of 200 bpm, for example, this corresponds to a wide range of 44 bpm. In contrast, MIT or zone 3 is defined as 83-87% of HRmax, which corresponds to a range of 6 bpm using the same maximal heart rate. So, it goes without saying that it is easier to hit the “sweet spot” in the higher intensity zones, as they are more narrowly defined.
Figure 2: Commonly applied training session models across intensity zones among Norwegian world-leading athletes in Olympic endurance sports [v].
A recent research article on training session models found that Norwegian elite athletes in Olympic endurance sports perform most LIT sessions in zone 1 and only a limited extent in zone 2[v] (see Figure 3). However, in some cultures zone 1 has an “image problem” due to a “no pain, no gain” mentality and the fact that zone 2 might be more time-effective. For some, the concept that one sometimes must train slower to become faster is hard to grasp. Along the same lines, some people see the easier LIT training (zone 1) only as a “recovery” or junk mile zone.
So, what else does research tell us? Unfortunately, we have very limited research on LIT of relevance for elite endurance athletes. In fact, there is a huge problem with studies looking into LIT: they are often short-term (10 weeks or less), whereas LIT adaptations often happen over the course of a career (10-15 years). Another problem is that in many studies intensities are not matched in a valid way. While matching training loads based on work done or energy expended can help ensure that individuals are exercising at appropriate intensities for health benefits or recreational fitness, but this way of “measurement” may not be as useful for coaches working with elite athletes because the goals and demands of the training are different. First, elite endurance athletes can train very large volumes of LIT without accumulating fatigue, which is not the same for HIT where only small amounts can cause strain. Second, research on moderately trained individuals are not valid for elite athletes who can sustain much higher speeds or power outputs during LIT. They can maintain proper technique and perform effectively for a long time without being restricted by work or energy constraints - provided they are optimally fuelled. HIT is a different scenario. During HIT, athletes are working closer to their maximum capacity, where work or energy constraints become much more evident and limiting.
Figure 3: Annual training intensity distribution of Norwegian Olympic endurance athletes [vi].
Therefore, the best evidence we currently have is to look retrospectively at how the most successful endurance athletes distribute their training over different intensities and, for example, how they perform their LIT. World-class endurance athletes with high annual training volumes (Figure 3) are exceptionally good at calibrating/aligning the session execution with the session goal. In terms of intensity, this means that they nail the correct intensity parameters according to the goals of the session. They then record the session correctly, so there is consistency between the goal of the session, the execution and the documentation. Being precise in terms of the intensity of the sessions is extremely important for all intensities, including LIT training, especially if we consider that it accounts for up to 90% of the total training volume in endurance sports.
Furthermore, if we bear in mind that it takes about 15 years (or over 10 000 hours) for an athlete to reach their potential, and up to 90% of these training hours are LIT, it would make sense that finding the “sweet spot” of LIT as well is important. It is probably also clear for most that it is completely different to do a 5-hour session at 60% of HRmax versus 80% of HRmax. But which is correct and why? Both options can be beneficial and generate a positive stimulus, but come with totally different “costs”. Training harder taxes the body more than if one trains easier, leading to a longer recovery time. Comparing “costs and benefits” of two 5-hour rides with different average heart rates might seem far-fetched but we can use an example to make this concept clearer: Let us compare the 60% versus 80% of HRmax with a purchase decision. If we can choose between paying more or less money for an identical product (e.g., you can choose between paying 3000 or 10 000 Euros for (almost) the same bike), most of us would choose to pay less. If we invest in the more expensive one, we have to be aware of the consequences which is that we have less money to buy something else. The same applies to training; if we do LIT sessions too hard, we must reduce something else as a consequence. For instance, not being able to do the MIT or HIT sessions at the desired intensity or having to lower overall training volume. These are the considerations that must be made carefully and in advance.
In a previous blog post we introduced the concept of risk management to facilitate better decision making. If the risk is low and the likelihood for a positive outcome is high, then it is a no brainer. If the risk is high and the outcome low, then the decision is easy as well. The problem is that most decisions are not so clear cut, such as in the case of differentiating between zone 1 and zone 2.
As we have explained before, the problem with applying training session models of elite athletes is that elite athletes can move at a much higher velocity than most of us at an effort level which is low for them but would be hard for most of us. For some recreational athletes it might not even be possible to stay in zone 1 because they are so inefficient or metabolically ineffective (e.g., for an amateur runner it can be hard to keep their heart rate <70% HRmax or lactate <1.5mmol/l). In contrast, world class athletes who have trained well over years are usually exceptionally efficient and effective in their trained modalities. The modality, in fact, is another variable that can make it difficult to determine the correct effort of LIT. A world class cyclist can have under 1 mmol/l in lactate when cycling with a heart rate of 150, whereas the same athlete would have over 3 mmol/l in lactate when skiing or running at the same heart rate. In some sports the surface or terrain chosen will also have an impact on the “cost” of the session. Running 2 hours on a soft surface feels a lot different than running 2 hours on asphalt, and 2 hours of running on an uphill is a lot different than running downhill for 2 hours, even if the heart rate is the same.
So, how do we find the optimal balance between “risk and reward” or “cost and benefit”? The parameters below can help you to make better decisions:
Total volume trained: The more you train, the less margin for error in intensity control and distribution. Here, mechanical constraints also play a role. Runners can’t train as much as for instance swimmers or cyclist because of the high mechanical load of running. Therefore, runners probably can/should train a little harder in LIT sessions as their total volume of training is significantly less compared to a swimmer or a cyclist (or they can use cross-training to compensate their lower volume).
The “need” to control the LIT intensity for a recreational athlete training 5 hours per week is also less than a professional athlete training 35 hours per week.The training modality and environment: Different sports can lead to a completely different “cost” even at the same heart rate. The muscular load/mechanical stress of the body is also different when running on hard or soft surface or when running up or down a mountain. The cost of different training environments also must be considered (e.g., it is harder to train at altitude compared to sea level).
Age and experience of the athlete: Older/more experienced athletes generally train more but need longer time to recover, usually benefitting from lower LIT intensity if they maintain training volume.
Session duration: Longer sessions require more experience to hit the correct intensity from the start, as prolonged exercise can shift thresholds and hence training intensity zones[vii].
Technique: “If it is worth doing, it is worth doing it right”. Correct technique should always be a priority. This can in some sports be a very challenging task as a correct technique comes at a higher cost. Speedskating or ski mountaineering with correct race technique is hard, hence it might require doing less LIT training in the specific sport and rather do the LIT training in an alternative sport like running or cycling.
The bottom line is that there is still much to learn about the optimal intensity for LIT, but the available evidence and the practices of elite athletes suggest that a conservative approach may be beneficial. Athletes who carefully manage their intensity can train more consistently and with greater volume, which supports sustainable athletic development. We have worked with several athletes who have seen significant improvements after reducing the intensity of LIT training with up to 10 heartbeats less per minute. We hope that future scientific research will further clarify the advantages and disadvantages of performing LIT at different intensity levels within the recommended range. In the meantime, we encourage athletes to experiment with different intensities during their LIT sessions to better understand how this impacts their performance and recovery. Maybe slightly lower intensity will allow you a higher quality of key sessions, better training-adaptation or make you tolerate more training too?
At MYRA, we’re here to help you navigate these nuances in your training. Whether you’re an elite athlete or just starting out, our evidence-based approach and expert guidance can help you optimize your performance. Contact us if you have any questions and join our newsletter for more insights and practical tips!
[1] https://olt-skala.nif.no/#ventilasjon_m
[2] How 3-zone models often used in science can be aligned with a 5-zone model used in training practice, is explained well by Stephen Seiler here: https://www.youtube.com/watch?v=NPwyk9B0j-s
[i] Tønnessen E, Sylta Ø, Haugen TA, Hem E, Svendsen IS, Seiler S (2014) The Road to Gold: Training and Peaking Characteristics in the Year Prior to a Gold Medal Endurance Performance. PLoS ONE 9(7): e101796. https://doi.org/10.1371/journal.pone.0101796
[ii] Stöggl TL, Sperlich B. The training intensity distribution among well-trained and elite endurance athletes. Front Physiol. 2015 Oct 27;6:295. doi: 10.3389/fphys.2015.00295. PMID: 26578968; PMCID: PMC4621419.
[iii] Seiler K. S., Tonnessen E. (2009). Intervals, thresholds, and long slow distance: the role of intensity and duration in endurance training. Sportscience 13, 32–53.
[iv] Sperlich B, Matzka M and Holmberg H-C (2023) The proportional distribution of training by elite endurance athletes at different intensities during different phases of the season. Front. Sports Act. Living 5:1258585.doi:10.3389/fspor.2023.1258585
[v] Tønnessen, E., Sandbakk, Ø., Sandbakk, S.B. et al. Training Session Models in Endurance Sports: A Norwegian Perspective on Best Practice Recommendations. Sports Med (2024). https://doi.org/10.1007/s40279-024-02067-4
[vi] Øyvind Sandbakk, Espen Tønnessen, Silvana Bucher Sandbakk, Thomas Losnegard, Stephen Seiler, Thomas Haugen. Best-practice Training Characteristics as described by World-class Norwegian Coaches in Endurance Sports. Sports Medicine. In revision.
[vii] Stevenson, J.D., Kilding, A.E., Plews, D.J. et al. Prolonged exercise shifts ventilatory parameters at the moderate-to-heavy intensity transition. Eur J Appl Physiol 124, 309–315 (2024). https://doi.org/10.1007/s00421-023-05285-2
