Most endurance athletes have heard the terms VO2 and VO2MAX, but what do they really mean? In this episode, coaches Neal Henderson and Mac Cassin breathe some life into this sometimes confusing topic.
Most endurance athletes have heard the terms VO2 and VO2MAX, but what do they really mean? In this episode, Wahoo Sports Science coaches Neal Henderson and Mac Cassin breathe some life into this sometimes confusing topic. What's the difference between the two terms? How do you calculate and improve your VO2MAX? Do triathletes and time trialists need to do VO2 workouts? What happened to Neal's hair?
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Neal Henderson 0:00
Hello and welcome back to another episode of The Knowledge podcast brought to you by Wahoo. I'm Neal Henderson, head of Wahoo Sports Science.
Mac Cassin 0:08
And I'm Mac Cassin, Senior Sports Scientist with Wahoo. Today we're talking about VO2, aka the volume of oxygen used by your body to produce movement. Most people hear the term VO2 they either think about it as a kind of workout, or they think aboutVO2 Max. We'll touch on both of those. But there's a lot more you should know when it comes to vo two, we are going to be throwing around more numbers than usual. But don't worry, there is no written test at the end.
Neal Henderson 0:32
Oh, darn it, I would like to have a test for everyone. Maybe even a VO2 Max test. What do you think Max? I mean Mac! Ha! Slip of the tongue. Alright, well, let's get into the business here. So with VO2, the V represents volume. And when we use the V in the context of VO2 or VO2 Max, we're talking about a rate of consuming or utilizing oxygen. So it's a rate of using oxygen. Typically, we look at this as liters of oxygen per minute, or which is an absolute VO2 value or in milliliters of oxygen per kilogram of body weight per minute, which is what we call relative VO2 to notice didn't say Max with either of those. I said VO2 because VO2 is just that rate of utilizing oxygen either absolute liters per minute or relative MLS per kg per minute.
Mac Cassin 1:40
Some good units, they're always fun. Personally, when we work with VO2, I prefer to look at it in absolute terms. And that's kind of just because of how my brain works. And it's a lot simpler for me to think of in that way. Because we know that basically one liter of oxygen consumed will be about five calories burned permanently and on a bike, it means you'll produce about 75 watts. So when I break it down to that it gets rid of the whole changing per kilogram, which Yeah, that's the way people like to represent that. But my brain doesn't like dividing by more than one thing.
Neal Henderson 2:12
Yeah, it's math. And so there's gonna be some math coming ahead. So just be aware, we're gonna, we're gonna do it. So the VO2 is not just the air that you're breathing in and out, it's really what is being delivered, and then what's being utilized. So your breathing rate is not your VO2 to breathing is your breathing in air that is not 100% oxygen, so only about 20.9% Oxygen. So at rest, we typically take maybe around six to eight breaths each minute. And each breath on average at rest is maybe half a liter, that's like three to four liters of air being delivered, but it's only 20% or so 21%. So that's only about point six 2.8 liters of oxygen being delivered. That's not through what you're consuming, consumption is less because, at rest, we have a minimum amount of the VO2, which that's kind of like your resting metabolism effectively. So again, you can measure this, we can go into the lab, we can lay it down, and we can actually measure your oxygen consumption at rest and get what your resting metabolic rate is. And that's kind of your lowest level of VO2. The opposite end of that spectrum then is your VO2 max when you are working as hard as you possibly can then this is the maximum amount of oxygen that your body is using. When we think about the air that we're breathing in, we can have individuals breathing upwards of 200 liters of air per minute 200 liters of air again 20% 20.9% oxygen that's over 40 liters of oxygen being presented to the lungs. But the highest VO2 max values that we see in humans are closer to like six or seven liters of oxygen. So there is a significant outpacing of the delivery of oxygen to the lungs versus the actual uptake and consumption or utilization of that we typically break the VO2 out into a central side of things which is the delivery of the oxygen to tissue and that's based on your hemoglobin mass or the number of red blood cells which is where the hemoglobin is in the oxygen-carrying capacity and then your heart rate and amount of blood that it pumps every beat which is your stroke volume and the combination of those two things are your cardiac output. And that really is kind of the central side of things. So the heart pushing blood that carries the oxygen being delivered to your muscle is one part of VO2 max. So moving to the peripheral Mac. Talk me through it.
Mac Cassin 4:56
Yeah, so the peripheral is really you know how much oxygen your muscles can utilize. So when your muscles are working, when they're working aerobically, you're going to be transporting that oxygen from the blood into your muscles into the mitochondria, those little powerhouses of the cell, as we all know, and there's a limit to how much oxygen your mitochondria can process. And one of the key things with training is increasing the number of mitochondria you have. And so more mitochondria means you can utilize more oxygen. So your VO2 Max would increase, you're limited on that peripheral side by the muscles that are working. And there you know, we'd say their quality of how much mitochondria they have some of its then that capillary density, how much blood can you spread across those different muscles. And for some people, this is going to be an issue for about point oh 1% of the human population. But while you can increase the number of capillaries in your muscles, you can increase the number of capillaries in your lungs. And so if your muscles are just chock full of mitochondria, and you can work out really, really hard produce a lot of power, then the area in your lungs, capillaries, there can be a limit to how much oxygen you're bringing in compared to what your muscles can use. Now, again, that's not something to be concerned about. For most of us, I just find it to be one of those fascinating things about some individuals out there.
Neal Henderson 6:15
Pulmonary diffusion limitation. Hmm,
Mac Cassin 6:17
yep,
Neal Henderson 6:17
yep.
Mac Cassin 6:18
And so the other part when we talk about that peripheral, it's the muscles being used. And using larger muscle groups, obviously, those are going to produce more energy use more oxygen, and using more muscle groups will also require more oxygen. That's why you see that cross country Nordic skiers basically have the highest recorded VO2 Max because they're using their legs maximally, and their core and arms. It's the same reason. You'll also see that if you test a triathlete their VO2 Max while running will be a bit higher than while cycling because again, there are more muscles working. So there's more demand for oxygen, you can even increase VO2 max slightly if you breathe through a really small tube instead of full breath because your diaphragm is working hard. But that's not a fun way to increase the
Neal Henderson 7:03
I would definitely not recommend that. So if we pull back to the big picture, again, the VO2 max value that anyone has is to some degree related to genetics, what you have from a starting point that you get from your parents is going to have some prediction on how high your VO2 Max can rise. Partially because heart size and cardiac output are trainable to a degree but not unlimited. And then also, interestingly, your mitochondrial DNA capacity is passed by your mother. So choose your parents, well, if you want to have a really big VO2, Max,
Mac Cassin 7:39
And make sure that they're very fit at the time because there's some epigenetics at play where if someone's pretty fit, they're more likely to pass on those good genes they have at the time.
Neal Henderson 7:49
Genes that have been turned on with training. So training, as you mentioned, can change your VO2 max to some degree, but it is not just unlimited, you can't just say okay, I'm staring at this level, and I'm going to increase with training up to the level of an Olympian, some of us have a lower ceiling. And that's just how it is, we can though change a few things. Number one, if we think about body weight, there are some changes in relative VO2 max because that is in milliliters of oxygen per kilogram of body weight per minute. And so if we decrease our body weight, we can increase that relative VO2 max to a degree but it wouldn't change your performance like riding on a flat road or on a velodrome because there's very little gravity that is a factor in those types of events.
Mac Cassin 8:35
You can also increase your total muscle mass to prove VO2. Because again, the muscles are what's sucking up the oxygen. So larger muscles more mitochondria, that'll bump it up. But again, as you said, there is a limit there to what you can do.
Neal Henderson 8:48
So in cycling, generally speaking, there's a really high correlation or relationship between your power that you can produce during a four to five-minute maximal effort and what your VO2 maxes, we often use that term then max aerobic power when we're talking about the power at VO2 Max. Again, it's a piece of the puzzle. It is not the be-all-end-all. So let's look into a couple of other aspects here. So it's not just about your max vo to that's an important factor in endurance performance, but what you sustain as well as then what your economy is.
Mac Cassin 9:23
Yeah, so when we talk about the economy for cycling, specifically, we're talking about how much power you're producing for a given amount of oxygen. And that can vary pretty significantly. And generally, as you get fitter, you're going to be able to produce more power with the same amount of oxygen which is why sure maybe your absolute VO2 Max will hit a plateau and it will increase but there are other improvements that can be made. So you can produce more power with that same VO2 Max.
Neal Henderson 9:51
Exactly. So let's look at some examples. Note we're getting into some math. We're going to look at two examples of an individual with very high efficiency, which is about a 25% efficiency versus somebody with very low efficiency in cycling that we would consider closer to about 20%. Efficiency. If we have two individuals that both have the same VO2 Max four liters of oxygen, that's four liters of oxygen per minute, the person with high efficiency at 25% would be producing closer to 80 watts per liter of oxygen consumed, which would give them about 320 watts at VO2 max or at their max aerobic power, the same VO2 Max for this second individual with low efficiency of 20% would only give them about 65 watts per liter, which would then yield about 260 watts at their VO2 Max. So both with a similar VO2 Max with these dramatically different efficiency levels will impact their power production significantly. 260 Watts low efficiency versus 320 watts for the high efficiency for the same VO2 Max.
Mac Cassin 11:05
Yeah, that's a pretty big discrepancy there. And it can become even more exaggerated or pronounced when you are talking about what percentage of VO2 max is someone's FTP.
Neal Henderson 11:16
Yeah. So if these two individuals that we talked about with the high efficiency and low efficiency both had a similar level of training, and both reach their FTP at about 80% of their VO2 max, the high-efficiency rider would be producing 256 watts at their FTP, and the low-efficiency router would only be pushing 208 watts at their FTP, if they both weighed 80 kilos, they would both have the same 50 mL per kilo per minute, relative to VO2 max. But their sustained power at FTP would again be very different. And if you looked at their time up a climb, it would be varied not based on their VO2 Max but based on the power that they're able to sustain at their FTP, which for the high-efficiency rider would be 3.2 watts per kilo, and the low-efficiency rider would be at 2.6 watts per kilo in this example to the difference in speed would be almost 20% for climbing.
Mac Cassin 12:12
And it goes beyond. Or you can go a bit deeper when you're looking at these differences in inefficiency if you look at the calories consumed for a given effort. So the example that we just walked through is setting them at different power outputs based on the relative efficiency, we can flip that around and just look at, say the riding at the same power and see what that looks like. So for a bit of background, when we talk about calories consumed on the bike, you know, generally, if you have a power meter, you'll get a kilojoule work completed for a ride. And the general rule is you can convert that from one kilojoule is equal to 1k Cal burn, technically speaking 4.182 kilojoules equal one kilocalorie, it might be easy to think, oh, I need to multiply that kilojoule number by 25% to get you to know the real number. But what's actually going on is that kilojoule value is what's being put through the wheels, your body is only about 25% efficient, like what we're talking about. So really one kilojoule at the wheel is equal to four kilojoules of internal work. So four kilojoules of internal work go to one kilocalorie.
Neal Henderson 13:18
So multiplying by four, and then dividing by four is kind of what you're doing that right.
Mac Cassin 13:22
Yep, exactly. So now we look at two riders riding at 200 Watts, these numbers we've actually pulled from people we've tested in our lab. So these are not hypothetical values. These are actual recorded values. So we have these two subjects riding at 200 watts for one hour, they would both do 720 kilojoules of work at the wheel, that's just watts or joules per second. So there's no changing that
Neal Henderson 13:48
3600 seconds, times 200 Watts gives us that.
Mac Cassin 13:53
So one of these riders, the higher efficiency rider only burned 620 calories for that one hour, while the lower efficiency rider burn 785 calories and as because one of them only needed 2.35 liters of oxygen to produce those 200 Watts and the other one needed 3.05 liters of oxygen to produce that same 200 watts.
Neal Henderson 14:19
So efficiency is one of those things that will impact how much output your body is putting into the pedals for a given amount of VO2. There are a couple of things that can improve or change your efficiency. Strength training can actually improve your exercise economy on a bike, neuromuscular training, improving your coordination and firing the correct muscles to produce power and not firing those muscles that counteract your power production will also help to improve your economy or efficiency and, you know, you can go the opposite way of decreasing your efficiency. See, by getting out of the saddle by moving your body a lot earn and pedaling at a very high cadence, all of those things will significantly decrease your efficiency. Alright, so after economy, one of the other big things that we do look at in a laboratory setting is the fraction between the amount of co2 that is produced versus the amount of oxygen that is consumed. And this is what we call the respiratory exchange ratio, or Vco2 divided byVO2 to So volume of co2 produced divided by the volume of oxygen consumed. This will tell us a bit about what fuel your body is actually oxidizing an RA our value of 0.7 would indicate that somebody is using burning oxidizing 100% fat as the fuel and an RTR value of 1.0 or higher will indicate that somebody is using 100% carbohydrate in their metabolism. In the middle of that, you have an AR AR value of point eight five, which is then a 5050 mix of carbohydrates and fat.
Mac Cassin 16:17
And that comes down basically to the fact that carbohydrates, shockingly, when you burn them produce carbon dioxide, which is then breathed out. So as that amount of co2 increases, it's indicating that more carbohydrates are being used. And so that's how we can do some snooping into your insights without actually seeing any of that stuff happening.
Neal Henderson 16:36
Yep, that's just stoichiometry. If you remember your chemistry, interestingly, you can go well over 1.0 on an AR AR value, because you get additional co2 That you exhale, when you're at a very high intensity above what your VO2 Max is you call in your nonoxidative breakdown of carbohydrate or anaerobic metabolism, which gives us some energy production, but also lactate and hydrogen ions or acid and those get buffered and it is the buffering from the bicarbonate that yields extra co2 That you exhale and blow off. So when you start breathing really fast, because you're working hard, partially it's that you're trying to exhale and blow off that additional co2.
Mac Cassin 17:20
Yeah, for the buffering, you can think back to if you're in grade school and made a volcano out of vinegar and baking soda, that expansion of gas, that's a much more exaggerated version of what's going on in your blood when your blood is trying to buffer take away that acid that's being built up. That's some of the breakdowns of when we talk about VO2 in terms of what it means for your body. The other component here to VO2 is it's often just a workout generic workout type.
Neal Henderson 17:46
The same intensity that people talk about VO2 max intensity.
Mac Cassin 17:50
Yeah, they'll say I have a VO2 workout today, just like you might say I have a threshold workout or a base workout. Really what that means or how it's been defined, at least in the literature is VO2 workout is a session that's aiming to accumulate basically as much time as possible at or above 90% of your VO2 Max.
Neal Henderson 18:08
Which that level has been shown to stimulate some of the central adaptations in terms of increasing cardiac output.
Mac Cassin 18:16
Yeah, and one of the things that are significant and have been proven again and again with more recent research is you can get that 90% accumulated time, in a lot of different ways you can do longer more traditional like two to six-minute blocks at around your maximal robot power. Or more recently, there's a bigger push for micro intervals. So something like the classic tobacco of 20 seconds on 10 seconds off 4020s, which we're a big fan of 30 fifteens is another new one. But you can kind of sense a pattern here that your recovery is half the duration of your micro interval. And the real difference between those two types of efforts is that for the micro intervals, the power you need to hold is aiming to hold is going to be higher than it would be for the steady-state VO2 intervals.
Neal Henderson 19:01
They're often pretty close. But even a little bit above what that kind of sustained power could be at a maximal level. So that Max aerobic power is good for sustained long efforts for 234 minutes. And I'm not a big fan of those five and six minutes, they're just very, very difficult to do so doing those 10 times two minutes for me is more preferable than doing say four by five minutes at that high intensity. But you know, to each their own the micro intervals, you might do something like three sets of eight times 40 seconds at 110% of Max aerobic power with 20 seconds recovery and say five minutes recovered between those sets and you would be accumulating a very similar total amount of time at VO2 max.
Mac Cassin 19:44
And the type of those intervals that you go for can kind of depend on what your goals are what time of the season it is for us being up here in Boulder, we generally do a lot more of the micro intervals because we're training at altitude a lot of times we're racing down at sea level so we need to get the muscles used to dealing with higher power outputs even though the long sustained ones have their place but as Neil said we're not the biggest fans of them.
Neal Henderson 20:07
Yeah, up here you know there is a reduction in our VO2 Max because of the reduced pressure. If we only did those longer intervals at altitude then we would have some reduction in our ability to sustain that higher power production that is going to be required for success at sea level. So that's kind of the idea behind that though.
Mac Cassin 20:25
And the last thing to always know about a VO2 workout is they're always going to be hard.
Neal Henderson 20:30
Yep, there are no easy vo two sessions like that. So some of the main takeaways here next time you hear the term VO2 don't immediately just think of VO2 max that is a component of it. It's the highest level but there's a vo two at any end every level.
Mac Cassin 20:46
And VO2 Max is important but it really isn't something to get overly focused or obsessed on. It's something you know we can even kind of back-calculate from our ramp test but we don't do that because it doesn't give you any actionable stuff. It's not going to change your training knowing what that VO2 level is.
Neal Henderson 21:03
Yep. And training can change your VO2 max to some degree there is definitely a genetic relationship and bodyweight changes can also influence your relativeVO2 max but those changes in VO2 will happen with a proper training schedule balanced with rest and recovery. Your real goal is to be able to produce more power for a given time or to be able to sustain a given power output for a longer period of time or to be able to repeat a necessary power output more times before you fatigue and that's what we're trying to do with training. So whether or not we see a change in VO2 Max we could still be seeing a significant improvement in actual performance without a change say in a laboratory vo two max settings so don't stress out if you don't see a change if you've done a lab test and you haven't seen much of a change with training.
Mac Cassin 21:51
There's no one size fits all best gold standard VO2 workout you know in my experience coaching and my own personal training I find that the best vo two workouts are the ones that you like the most are better put dislike the least I personally really like micro intervals I cannot stand long VO2 intervals so I do a lot of micro intervals. The bestVO2 workout is one that you actually do. Exactly. That's it for another episode of The Knowledge Podcast by Wahoo. Until next time, keep breathing