What is VO2 Max?

If you hang around endurance athletes long enough, you’ll eventually hear mention of VO2 max. Sometimes they’ll refer to it in an almost reverent tone, though that’s still no guarantee they actually understand what it is (and isn’t). This is one of those terms that’s tossed around a lot and is something that many athletes will pay to have measured, demonstrating that its import is poorly understood.

For starters, unless you are an upcoming elite endurance athlete, your current VO2 max is irrelevant. VO2 max is the maximum amount of oxygen that your body can use, or the highest-intensity effort that is still relying on predominantly aerobic metabolism. Expressed in either absolute (L・min -1) or relative (ml ・kg ・min -1) terms, it’s an indicator of one’s endurance potential. It is multi-factorial, determined by the body’s ability to recruit motor units, the pulmonary and cardiovascular systems’ capacity to deliver O2 to working muscles, and the oxidative and metabolic pathways of those working muscles to make use of it.(3)

If you show up at an Olympic Training Center hoping to make a US development team, they’re going to test this. Most elite endurance athletes (distance runners, cyclists, cross-country skiers) will have a relative VO2 max in the high 70s to 80s. There are exceptions, such as highly successful athletes whose VO2 max might not appear to predict what they actually achieved, and, of course, those with remarkable results on a VO2 max test who never went far. It can’t measure things like mental toughness, pain tolerance, or the ability to sustain the necessary training volume and resist illness and injury to compete at the highest level.

Then why do we talk about it so much? Good question. Probably because it is relatively testable compared to mitochondrial density, enzyme activity, or even lactate levels. Knowable or not, “VO2 max interval” is useful as a descriptor of the intensity required to achieve a response at the highest end of aerobic capacity. In two words: very hard.

VO2 max differs by sport, so the same person may have a different number for running, swimming, and cycling. But again, it’s only one predictor (among many) of potential. The upper limits are genetically determined, and the more trained one becomes, the smaller the possible incremental gains and the harder they are to achieve. If you just got up off the couch, you will see greater gains than someone who’s been training for a long time. But that’s true of almost any fitness metric—the initial gains are more easily won than those tiny percentages that separate the medalists from the rest of the pack. It’s why endurance sports like cycling, cross-country skiing, swimming, and running require intense, high-volume levels of training at the most competitive levels.

Workouts can be a full-time job for elites, but that doesn’t mean it has to be so for our purposes. As recreational athletes, or just human beings who want to optimize our health and well-being, we can vary our training levels to keep our bodies and brains engaged and continually improve our fitness.

Let’s use an analogy of a manufacturing and delivery system to explain the changes in the body’s ability to use oxygen at a high work level. The goal of training is to spare muscle glycogen, decrease lactate production, and to get our muscles to produce more force at this intensity. To do this, a working muscle needs to recruit more motor units (a motor neuron and the muscle fibers it innervates)—think of this as getting management to allocate more resources to our project. With more motor units on the job, we need to keep them supplied with fuel (ATP). The mitochondria are the factories that produce ATP. We enhance overall energy production by building more factories (scientific term: increased mitochondrial density). The greater demand on our factories for their products requires a larger volume of blood (the transport medium, shipping “inventory” like oxygen and nutrients in and exporting or recycling what’s used up) and more secondary roads around those factories (capillaries surrounding the working muscles) to deliver the inventory. Finally, the workers in our factories must be more productive to keep everything humming; enhanced aerobic enzyme activity does that, giving us greater fitness upon which we can build.

To drive this analogy into the ground: raising VO2 max allows our engine to run harder because our delivery system is well engineered and robust, able to keep up with the surge in demand that working hard imposes on it. Put another way, indoors or out, you’ve felt the difference between climbing a hill when your fitness is “less than” and when you’re at the top of your game. You can push hard and it feels so much better than the same effort when you aren’t well trained, like a sleek sports car screaming along a highway compared to a rusted-out beater that sounds like it might not make it to the next exit.

Resources

1. Power Training Levels, by Andrew Coggan, Ph.D., Training Peaks Coaching Group.
2. Training and Racing with a Power Meter, Andrew Coggan and Hunter Allen, Velopress.
3. Using Intervals to Target VO2 Max Adaptations, Stephen McGregor, Ph. D., Training Peaks Coaching Group.
4. Total Heart Rate Training, Joe Friel, Ulysses Press, 2006. Page 47.
5. Physiological Fitness – Aerobic Capacity, Joe Friel, Training Bible.com.
6. VO2 Max, Aerobic Power and Maximal Oxygen Uptake, Sports Fitness Advisor.

References

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2.    Chia-Lun L, Wei-Chieh H, Ching-Feng C. Physiological Adaptations to Sprint Interval Training with Matched Exercise Volume. Med. Sci. Sport. Exerc.
3.    Egan B, Zierath JR. Exercise Metabolism and the Molecular Regulation of Skeletal Muscle Adaptation. Cell Metab 17: 162–184, 2013.
4.    Hawley JA, Hargreaves M, Joyner MJ, Zierath JR. Integrative Biology of Exercise. 159: 738–749, 2014.
5.    JD M, Hicks AL, JR M, RS M, Green HJ, Smith KM. Muscle performance and enzymatic adaptations to sprint interval training. J Appl Physiol 84: 2138–2142, 1998.
6.    Little JP, Safdar AS, Wilkin GP, Tarnopolsky MA, Gibala MJ. A practical model of low-volume high-intensity interval training induces mitochondrial biogenesis in human skeletal muscle: potential mechanisms. J. Physiol.
7.    Martin M, Gibala M. Physiological adaptations to interval training and the role of exercise intensity. J Physiol 595: 2915–2930, 2017.
8.    Rønnestad B, Hansen J, Vegge G, Tønnessen E, Slettaløkken G. Short intervals induce superior training adaptations compared with long intervals in cyclists – An effort‐matched approach. Scand J Med Sci Sport 25: 143–151, 2015.
9.    Sylta Ø, Tønnessen E, Hammarström D, Danielsen J, Skovereng K, Ravn T, Rønnestad BR, Sandbakk Ø, Seiler S. The effect of different high-intensity periodization models on endurance adaptations. Med Sci Sports Exerc 48: 2165–2174, 2016.
10. Thum J, Parsons G, Whittle T, Astorino T. {High-Intensity} Interval Training Elicits Higher Enjoyment than Moderate Intensity Continuous Exercise. PLoS One 12: e0166299, 2017.
11. Wakefield BR, Glaister M. Influence of work-interval intensity and duration on time spent at a high percentage of {VO2 max} during intermittent supramaximal exercise. J. Strength Cond.