What is maximal oxygen uptake (VO2max), and how should you train to increase it?
Written by: Hans Kristian Stadheim
Coach Allround Team Aker Dæhlie NC/World Cup
Cross-country skiing requires many different physiological and psychological parameters to perform at the highest level. If you are interested in cross-country skiing and endurance sports, there is a high probability that you have heard of the expression “maximal oxygen uptake (VO2max). VO2max is usually associated with endurance sports, where a high uptake has been observed in several of the best female and male elite athletes in different sports (more on this later).
What many may not know is that an increase in oxygen uptake has also been shown to increase the quality of life, as well as life expectancy (1, 12). Normally, the maximum oxygen uptake will increase from the age one hits puberty until around 25-30 years old (17). After this, the uptake will normally decrease because of increasing age. On the other hand, with specific and correct training, a well-trained 60-year-old can have a higher VO2max than an untrained 30-year-old! Furthermore, it is entirely possible to increase oxygen uptake even after one has passed the age of 30. Studies have shown, among other things, that a individual who is in poor endurance shape can have an increase of as much as 10-30% if he/she trains correctly during a 8 to 12-week period. An increase of around 10% in VO2max will in most cases lead to a significant improvement in endurance performance for most endurance sports. This is probably one of the reasons why several athletes and coaches systematically try to increase the maximum oxygen uptake, at least in periods of the training season or an athlete’s carrier. When you also know that an 10% increase in VO2max can reduce the risk of death by as much as 15%, giving up to 15 extra years of good quality of life (= absence of pain and challenges in carrying out everyday tasks) (1, 12). In other words, there reasons are many both for trying to increase, or maintain your maximum oxygen uptake.
Figure 1: Difference in VO2max as a consequence of training status throughout life(12)
However, what exactly is VO2max, and what affects the value?
In addition, what could be some good advice from the sports scientific literature and research if you’d like to increase this.
In this article, we want to focus on precisely these two questions. As with previous written articles of Team Aker Dæhlie it is important to note that in both sports science and training there are no “conclusive methods”, or “cooking recipes” that can guarantee and give an exact result. Nor to the two questions above. However, we hope this article can give some good advice, knowledge, as well as be informative about this much-used expression in our sport of cross-country skiing. If nothing else it can light a spark of discussions for/between athletes and coaches for moving forward.
What exactly is VO2max?
The year 2023 actually marked the 100th anniversary of 'the maximal oxygen uptake' (VO2max). The concept was first described by Hill and Lupton in QJM in 1923 (15). The authors suggested an upper limit for oxygen intake depending on our cardiorespiratory system (heart, blood and lungs) and the ability they have to deliver oxygen to the working muscles (14). VO2max, or the maximum oxygen uptake is defined as;
'The maximum amount of oxygen (per minute) a person can absorb and use, and is a measure of a person's aerobic maximal capacity' (13)
The "V" in VO2max stands for volume, "O2" stands for oxygen and "max" refers to the maximum. Together, this is a measurement of the highest volume of oxygen your body can use during exercise and strenuous physical activity. The number is important because it will determine how much energy (ATP = the body's energy currency) your body potentially have the potential of producing through aerobic[1] energy processes in the mitochondria. VO2max is typically reported as milliliters of oxygen expended per kilogram of body weight per minute (ml · kg-1 · min-1).
Table 1. The table shows «normal values» for VO2max for adult women and men who are healthy and active (14)
To be able to measure how high the "VO2max number" is, this has traditionally been tested in a sports science laboratory. There is a lot of variation in test protocols, but on a general basis, the test usually consists of two parts.
The first part is a warm-up on low moderate intensity (i1 to i3/i4). In total this part lasts for 20-40 minutes. Part two is the actual VO2max test, which typically have a duration of 4-7 minutes. Often, the workload in the VO2max test itself gradually increases until the test subject reaches voluntary exhaustion (12).
VO2max values and athletic performance
In the enormous amount of academic literature on the topic "how to train to increase VO2max", there are several different theories and proposed methods. We have no aim to go thru all in this article. The aim is to give an overview, and present the methods and theories that science and research have observed to be beneficial if one wants to increase this physiological parameter. In addition, we would like to try and give you as a reader a recommendation based on the scientific literature that is available. It is important to point out that there is no evidence in the research literature that justifies the claim that one specific session, or model alone is more effective than all others. Despite some people claiming "4x4 minutes" intervals are superb vs. other methods for increasing VO2max. At least this is not supported in sports science.
Figur 2: VO2maks and expected time on a 10 km run (3)
As a good dish, all the ingredients in the training work are important, although in this article we focus more on the activities that probably, as well as hopefully give a high heart rate.
Sport's requirements for VO2max
It is known that the best endurance athletes in cross-country skiing have a VO2max of around 80-90 and 70-75 ml · kg-1 · min-1 for men and women respectively (18). This value is one of several physiological parameters that directly determine your performance and the level at which you can perform in cross-country skiing. There is like most other physiological parameters and genetical predisposition in how high VO2max number one can have. However, with out correct training you will never reach your full potential. Training that has the ambition to increase, or maintain VO2max has therefore also been considered important sessions in training for many athletes.
It is mainly the body's total hemoglobin mass (transport capacity of oxygen) and stroke volume (how much blood is pumped out per heartbeat) that directly determine how high VO2max an individual has. Since these two parameters are important, training that stimulates the development of these two components are therefore important and, if nothing else, most effective. It must also be mentioned that an increase in total hemoglobin mass will almost always indicate that you have more red blood cells, leading to an increase in the total blood volume. This is because each individual red blood cell (erythrocyte) contains haemoglobin. However, the amount of each red blood cell will vary between different people, men and women. The value is stated as an individual's haemoglobin value. Here, normal values are between 13.5-17 g/dl for men and 12.5-16 g/dl for women respectively (13). However, there is no correlation between those who have a higher hemoglobin value having directly higher VO2max. This only says something about the concentration, nothing about the total mass, as those with a lower value will compensate with a higher volume (14,15). As VO2max is an important parameter, it is therefore quite common for elite athletes (especially younger ones) in cross-country skiing to test the value one to three times a year, which several of the athletes who are in Team Aker Dæhlie (TAD) also do. This is done both to see what physical level one is at (aerobic capacity), but also to see how this value may be affected as a consequence of the training one undertakes. The testing of VO2max is often carried out when running, but several of the athletes on TAD test this value on more sport-specific movement when e.g. doble poling, classic or skating as one sees greater benefit from doing this.
Table 1: Differences in HBmass, red blood cells (RBCs), plasma volume (PV) and blood volume (BV) between the different age groups from the study by Steiner and Wehrlin 2011 (6)
So why test VO2max?
In 2011, T.Steiner and J.P. Wehrlin published a very exciting study that asked the question (17);
"How does VO2max affect people with endurance training as a consequence of age".
The results from the study clearly showed that VO2max increased significantly for those who completed endurance training compared to those who did not complete any exercise (control group) from puberty until they reached senior age (Figure 3). However, there was virtually no increase in VO2max between the ages of 21 and 28 years. This was despite the fact that the athletes who were 28 years of age both trained for several hours, and had done so for several years (Table 1) (17).
Figure 3: VO2max in athletes who did endurance training increased significantly compared to people who did not exercise. On the other hand, VO2max does not appear to increase further after the age of 21 (6)
It was also observed that the total amount of haemoglobin mass (Hb mass), the amount of red blood cells (RCV), plasma volume (PV) and blood volume (BV) there was no difference between those who were 21 and 28 years of age. On the other hand, both of these groups had significantly higher values than those observed in those who were 16 years of age. Hb mass, RCV, PV and BV were again higher than those observed in the control groups of similar age.
The point of highlighting this particular study is to also communicate that it is important to remember that the planning and implementation of each individual training session should take into account, among other things: age, performance level, training and recovery condition. This is also seen in elite sports, where the focus on a "high oxygen uptake" and measuring the value is something that is more focused on in younger athletes in junior and early senior careers, than those who are approaching 30 years of age. For these athletes the goal of a VO2max test might actually just be to control that the value is at an excepted “high enough value”, with the athletes focusing more on other physiological parameters. It is also important to remember that the general recommendations regarding training to increase VO2max must be seen in light of the principles of individualisation, overall load, adaptation, variation and progression. These principles were established as early as the mid-1900s, and are just as applicable today as when they were introduced. They are also equally important when discussing how to increase VO2max. However, one understands from data among elite athletes that a high VO2max number is important in many sports to be able to win medals in championships. So the question is how can one increase this physiological parameter most effectively?
"How to increase VO2max"
VO2max has a clear correlation with athletic performance in endurance sports with a competition duration of more than 3 minutes (Example in Figure 2). If the goal is to increase this number, intervals with work intensity above 85% of maximum heart rate (HFmax) are probably the most effective way to achieve this (16). This is part of the reason why intervals are often referred to by athletes and coaches as "quality training".
Table 2: The “OLT/Norwegian” model of 1-5 intensity zones for aerobic exercise (https://olt-skala.nif.no)
If you then think of intensity zones, this in Norway will be i-zones 3, 4 and 5, which are internationally referred to as "medium and high intensity training". This should not be interpreted as meaning that the other elements of the training work (I-zones 1 and 2) are not important, because they are in the overall puzzle. (You can read more about Olympiatoppen's intensity scale here: https://olt-skala.nif.no/ . Furthermore, other methods besides interval training such as: heat training, or altitude training is also carried out by athletes to increase VO2max by increasing total HBmass. We will not address these methods in this article. However, we have previously described our thoughts on how to best perform altitude training. Link: https://www.teamakerdahlie.com/training/blog-post-title-one-t6xb3
Different interval forms to increase VO2max
Different professional communities have different thoughts, as well as guidelines for which methods and training intensities they believe increase and maintain VO2max best. If you divide these methods very generally, you can say they are something like the following:
Short strokes/sprints (I-zone 6-7) (15-60 seconds x 6-10 repetitions) with maximum effort. Pauses as long as the pull, or twice as long.
Medium (I-zones 4 and 5) pulls (3-5 minutes x 4-6 repetitions) with high effort (87%--> of HFmax). Pause 50% of the duration of the draw.
Longer (In zone 3) Drag (8-15 minutes x 4-6 repetitions) with fairly high effort (80-87% of HFmax). Pause often 1-2 minutes.
All of the above methods are carried out as intervals. This means that you have an active part, before you have a part that contains a pause. Studies that have looked at individuals who have only completed "one run" with a duration between 8-20 minutes, such as 3000m running all-out, show that this is also a very effective way to increase VO2max (13,16). On the other hand, for most people, this costs much more psychologically to carry out, than to divide the same workload, and the total duration into more and shorter parts (intervals). Motivation, mental strain and injury issues are probably the most important reasons why one recommends doing interval vs "all out" sessions if you want to increase VO2max. These will also be three factors that affect which of the interval forms one both plans and implements.
Furthermore, if one looks at the work intensity at the different interval types, these vary, as well as the number of repetitions. This in turn will affect the total time one recommends with activity (i.e. the time one moves) to be able to get an expected/probable increase of VO2max (4,12,13,16). As one example, a classic 6-10 x 30-60 second interval of maximum effort will only have 3-6 minutes of active time. In contrast, the longer intervalls can have a total duration of up to 30-75 minutes, which in turn is twice as long as the medium and infamous 4 x 4 minutes. The risk of injury and mental strain will be higher the more intensive the intervals are, Short vs Long. This is aside the specific requirements that different endurance sports require. Because even though VO2max is important for both a cross-country sprinter (about 3 minutes) and a 50km (around 120-150 minutes), these two disciplines also have other requirements, which can therefore help influence the choice of interval types one should consider/choose above.
Despite the differences in design, most studies have observed that if the goal is to increase VO2max, all the three different interval types above will result in a greater increase than doing training at low work intensity (below 70% of HFmax) (5). This should not be misunderstood as e.g. low intensity and longer workouts with a lower heart rate are not useful, or "quality". This is illustrated in a meta-analysis by Bacon from 2013. In the study, they concluded, among other things; 'For untrained people, calm, low-intensity exercise also resulted in an increase in VO2max, although this increase was significantly lower than with high-intensity work' (5). Statistics and analyses from elite athletes show that around 75-90% of the total training work is carried out at low training intensity (18). Displaying the importance of this training! On the other hand, if the focus is solely on increasing VO2max, higher intensity training is probably the single most important exercise to increase your maximum oxygen uptake (16).
So what is the optimal "intensity" of intervals if you want to increase VO2max as much as possible?
The "optimal" work intensity
To give an accurate and unambiguous answer to this is difficult based on the academic literature. Much of the reason for this is that there are large differences in the baseline level of those who complete the studies and hence the increase observed in VO2max (ref the study by Steiner and Wehrlin in the introduction). Despite this, data suggest that intervals performed on medium intensity (I-zones 4 and 5) provide a greater and safer increase than work on short and longer intervals (3-16).
In a master's study by Boye from 2010, 23 female test subjects completed either 10x30-seconds (30 seconds "all-out" run with 3.5 min active break) or 4x4-minutes (4 min run at 90-95% of HRmax, with 3 min active break at 70% HRmax) 3 times a week for 8 weeks. The results of the study showed that there was a greater increase in the group that completed the 4x4 minute pulls (3.6% vs -0.5% increase) (6). Helgerud's studies at the end of the 2010s showed that short intervals can increase VO2max, but that the increase is not as large as in the groups that complete the medium duration of the intervals. It was also observed that the increase was lower in the subjects who completed intervals of long duration (4). This also coincides with several reviews and meta-analyses on the topic that have been published to date on the topic (5,9,10,11,16).
Data, on the other hand, from the best elite athletes in various endurance sports is harder to come by. Fortunately, there are some good articles, and from these it is known that these athletes often train significantly more around in-zone 3/low 4, than in-zone 4 and 5 based on analysis work of their training diaries. Part of the reason for this could be that elite senior athletes have threshold speed up to 85-90% of their HFmax (I-zone 3). In other words, they have a very high utilization rate of their VO2max at their given threshold speed. These athletes can thus have a very good effect of training this type of training also on their maximum oxygen uptake. They may also have reached a «plateau» where it is appropriate to focus on the utilisation rate of VO2max, rather than trying to increase this by 1-2 ml · kg-1 · min-1. This is also in line with the results and observations in the study presented by Steiner and Wehrlin from 2011 (Figure 2). On the other hand, for most people, and younger athletes who are juniors, or in early senior age, few will be able to work with such a high work intensity (% of HRmax) and duration during this form of training (there are exceptions). Therefore, based on the professional literature, one would say that i-zones 4 and 5 are the two most effective intensity zones if the goal alone is to increase or maintain VO2max.
In Team Aker Dæhlie, there is therefore great variation based on the development goals of each individual athlete to what extent the athletes focus on i3, i4 or i5 intervals in training. Those athletes who have as one of the development goals to increase the "engine" and capacity will have a much higher input of i4 and i5 intervals than those athletes who, for example, want to improve utilization rates of VO2max and get a higher threshold speed. This will also have an impact on the composition of the rest of the training. I would therefore remind at the end of this article of the principles of load, adaptation, variation, progression and individualization in the training.
Conclusion and "Take Home Message"
If one is to try to summarize the academic literature on this enormously large topic, there seems to be some good advice that is repeated in the studies that have seen the largest increase in VO2max:
The duration of the interval pulls should be between 3-5 minutes, and is completed 4-6 times so total time is over 15-20 minutes. For well-trained people (VO2max over 60), the total duration must be up to 25-35 minutes.
The work intensity should be above 85% of HFmax.
The breaks should not last longer than about 50% of the intervall length.
The interval type should be done every 3-4 days (2-3 times a week) for at least 6-8 weeks.
There are also results that indicate that it is an advantage to carry out the interval sessions progressively. That is, you gradually increase the workload from one interval to the next.
If you manage to complete the points above, most people will have an increase in VO2max of between 5-10%. The magnitude of the increase will be largely influenced by the initial level and genetic predispositions. In addition to getting in better shape and being able to move faster, there are also great health benefits associated with increasing VO2max such as increased life expectancy and quality of life.
Good luck with your training and hope you found the topic interesting.
References
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