What is VO2 max? It’s a measure of how much oxygen your body is capable of processing while engaged in high intensity aerobic exercise. Let’s say that you’re running or biking as hard as you can for about 5 minutes or undergo a ramped fitness test to exhaustion, you will most likely reach a point where you can no longer use your lungs to absorb oxygen, have your red blood cells hemoglobin bind to those oxygen molecules, have your heart distribute that oxygen rich blood, and then have your working muscles absorb that oxygen and use it to produce ATP by burning fat or carbohydrate. At low intensities, your body will burn fat and carbohydrate in some mix relative to the intensity of the exercise. At very high power outputs or running speeds your body will use carbohydrate almost exclusively to produce the ATP needed to do the task at hand. At some point, you can no longer process more oxygen and any extra power or running speed will come form anaerobic metabolism, where your body burns fuel incompletely without oxygen, a process which simply requires oxygen after the fact to burn the lactate produced as a result of incomplete glucose metabolism. Your body is always engaged in some low level of anaerobic metabolism, but for the most part, it only becomes a major source of energy for short bursts of high-intensity work, like when you’re sprinting or lifting weights.
Unless an athlete is relatively new to endurance sport, VO2 max is not a measure of how much oxygen your lungs can absorb or a measure of how much blood your heart can pump. Not everyone thinks this, but it is a fairly common misunderstanding. It could well be that for a given individual the limiting factor for their exercise performance could be due to a limit in oxygen absorption or blood distribution, but in most healthy individuals this is probably not the case. Early in an athlete’s career, their heart volume and efficiency can definitely be increased. Likewise, lung capacity can change with time. For an athlete that has been at their sport for a while, these two things are much less likely to occur.
Rather, VO2 max is more often a measure of maximal aerobic metabolism occurring on the cellular level as your mitochondria absorb oxygen and burn fuel with it. Your blood almost always leaves your lungs at it’s functional saturation level. Your heart almost always could pump anywhere from a few to several beats more than it is, even when you are exercising “as hard as you can.” So, what is it that limits VO2 max in most cases? Your cells’ mitochondria. The quantity of enzymes in all of your working muscles capable of using oxygen to produce the ATP needed to do work.
In a lot of ways, this is a good thing, because it means it’s more trainable than people may think. If you attribute your exercise limits to the volume and efficiency of your heart or lungs, then you may face a bleak future of limited potential for improvement, though this limit would be perceived. Rather, most of your aerobic limits, as well as your anaerobic limits, are attributable to the volume of slow twitch and fast-oxidative fast-twitch muscle fiber that you have and their training status… Ultimately, VO2 max is usually highly trainable. Of course, individuals very significantly in how much or little they respond to training and to different types of training. Likewise, an athlete may be near or far from their peak fitness. Still, VO2 max, like other things, is not static and is often not as much of a limit as you might think. Some athletes’ VO2 max will top out after a few years of good training, and they may stop improving or may see improvements in other areas. Other athletes may see their VO2 max increase for several years and end up at a much higher point than their modest beginnings would have indicated.
No matter how you think about VO2 max, what you attribute your limits to, or how long you’ve been an athlete, it’s good to remember that there’s almost always room for improvement and room to expand your perceived limits.
How do I improve VO2 max? In short, you exercise at or near an intensity level that requires you to process as much oxygen as your body is capable. The most common and likely most effective way of doing this is to do VO2 max intervals or aerobic capacity intervals of 2-6m duration with moderate to short recovery periods. As you do this, you will use your nervous system to recruit as many muscles as you have to use to produce the necessary power for such an effort, you’ll get your heart to pump almost as much blood as it’s capable, and you’ll get your muscles to burn fuel at the highest rate that their mitochondrial density will allow. It will also help your brain to become more familiar and comfortable with exercising at that intensity, and as your brain comes to learn and relearn your performance limits, those limits will gradually expand, as long as there is a hard basis for those expansions. Keep in mind that there are physical factors limiting your performance and those are what allow some athletes to perform better and worse than other athletes at certain things, but it’s always a dynamic interaction between the different parts of your body, including your brain and its perception of effort and exertion. Your brain is consciously and/or unconsciously aware of how many muscles you’re engaging, with what frequency and force, how much heat you’re building up in your body, what your heart rate is, what the oxygen, carbon-dioxide, and lactate content of your blood is, etc. etc. All of these things are integrated into a perception of effort, and whether you like it or not, or are aware of it or not, it affects and even controls how much work you can do and how well you can perform. This is, of course, an increasing area of interest among sports physiologists, and the degree to which your brain limits or even controls your performance limits is hotly debated, but I think it’s quite clear that both your physiology and your brain’s perception of it factor into the bottom line of workout or race-day performance.
Whatever the limiting factor may be among those four things, you will be addressing it. Whatever is most limiting to you at the time of your workout, you will be working out that system the hardest, which is kind of nice. Basically, it’s good to remember this fact. No matter what kind of workout you’re doing and no matter what system you think you’re working to improve, the weakest system that limits your performance the most will sustain the most stress and should be the system that undergoes the most improvement as a result. So that should take some pressure off, because your training doesn’t have to be “perfect” to help you improve. In fact, there’s probably no way to get it all just right, but there’s a few ways that will be as close as you can get, and will help your body to get it just right.
Regardless of how you think about your training, no matter what you think your limiting factor is, what your training status or personal history in the sport… if you go out and do 5x3m hard with 2m easy recovery, 3x6m hard with 3m easy recovery, or do a 40m threshold effort with 1-2m pick-ups every several minutes, then you’ll be stressing your body to bring about an improvement in your aerobic capacity/VO2 max.
VO2 max workouts: 5x3m, 3m easy vs. 3x5m, 3-5m easy vs 3x5m, 15-20m easy? What should I do? From the start, all of these workouts are excellent and for most people would be a fantastic way to increase their aerobic capacity.
5x3m, 3m easy: This workout is short and to the point. Lots of VO2, lots of neuromuscular training, and a healthy dose of anaerobic training. After the first 1-2m of the first effort, your body will be at or near it’s VO2 max during most of this workout and will provide you a good 10-12m of time stressing that intensity to it’s utmost. Your power will be high, so there will be a notable anaerobic contribution to the workout, which is why you’ll be breathing hard for 1-2m after each effort. This is also why this format of workout is good for your nervous system; it engages more muscle fibers and trains both slow and fast-twitch muscle fibers.
3x5m, 3-5m easy: Again, it’s a very efficient workout. Lots of VO2, much less neuromuscular stress, and much less anaerobic stress. This workout is probably the most classic VO2 workout, because there’s no way to really overshoot your aerobic capacity by much, because the efforts are long and the recovery is relatively limiting. You’ll get at least 12 or 13m at or very near your VO2 max, with less overlapping benefits to your anaerobic capacity and some benefit to your threshold.
3x5m, 15-20m easy: Clearly, this workout will take much longer, but will still stress your VO2 max quite a bit. You may, however, have the most stress to all systems previously mentioned. Because you’re well rested for each effort, the power and intensity can be much higher, thus stressing your neuromuscular systems more as well as allowing for a greater stress to your anaerobic capacity. All the while, you’ll get at least 10m or so at your VO2 max, and you get the added benefit of a bit of endurance training. In some regards, this workout could be the most race specific rather than fitness specific, as it were, because you’re doing some efforts well into your workout time with more accumulated fatigue, as you’re required to do in races.