Why maximal oxygen uptake is more important when cycling than running

You soon get the feeling that Oliver Quittmann has turned his hobby into a career when he begins to speak: «In sports science, you can implement what you research yourself.» The triathlete researches and teaches at the German Sport University Cologne and also works in his own interest to improve performance diagnostics. «You not only create graphics for better understanding; you can use findings in practice,» he says. That is undisputedly true, but it also requires a certain basic understanding of the context.

Energy has to come from somewhere. Whatever you do, your muscles need adenosine triphosphate (ATP) to work. Unfortunately, they have very little of it. A series of more or less complicated processes then kicks in. I talked to Oliver Quittmann about what happens in the body when cycling or running, how that can be measured and how it should be interpreted. It’s a big topic where many aspects play a role and things can quickly get in-depth. To make sure I took everything in, I asked him to stay on the surface for a bit before gradually diving in.

How do muscles get energy?
Dr Oliver Quittmann: That’s a vast field, but I’ll try to explain it as simply as possible. Basically, the body has many different energy supply routes which either use oxygen or don’t. That is why we generally talk about aerobic metabolism, where oxygen is present, and anaerobic metabolism, which takes place without oxygen.

Let’s start without oxygen.
Anaerobic metabolism enables the body to synthesise more energy in the same time, meaning more performance. If you sprint or pull off a short burst of speed, you’ll get a lot of energy in the short term. There are two essential aspects of anaerobic energy supply. Firstly, there’s the creatine phosphate system for very quick energy and at the beginning of an exertion. These supplies are used up after a few seconds. Then there’s the glycolytic system, which also leads to the net build-up of lactate. This requires only a few processes, the body can generate energy relatively quickly from glucose, i.e. sugar, with a few intermediate steps.

And what kind of energy supply do I need for the long haul, like a marathon?
If I’m looking for endurance, I need my body to processes the glucose to the extent that it reaches the mitochondrion. We use the term anaerobic for anything that has to do with the mitochondrion. Oxygen is used in the respiratory chain to create ATP molecules and produce water. Because many processes are necessary to get to these ATP molecules, it takes longer, especially if I also want to use energy from fats. Because these processes are slow, I can’t move as fast, but I can move for longer.

If you want to move as fast as possible for as long as possible, you need a good supply of oxygen. So, endurance athletes pay particular attention to their maximal oxygen uptake (VO₂ max). What’s that?
Maximal oxygen uptake describes the body’s ability to metabolise oxygen. We can’t directly measure what’s happening in the muscles, but we can measure the respiratory gases, which is done indirectly via calorimetry. That means the participant wearing a breathing mask and a turbine or lamella system being used to record how much air is being breathed back and forth. This determines the oxygen and CO₂ concentration, which are used to derive how much oxygen is absorbed and how much CO₂ is released.

What kind of strain are the participants put under?
Ramp programmes on the treadmill or ergometer are key to determining maximum oxygen uptake. They increase the strain constantly and relatively quickly. You might do a warm-up, then, after 8–12, or some say 6–15 minutes, start the ramp part. So, it’s not a very long-lasting effort; we’re talking about exertion for a relatively short period of time to the point of exhaustion. The maximum oxygen uptake is then given in millilitres of oxygen per kilogramme of body weight per minute.

Every quality sports watch churns out a VO₂ max value these days. What’s your take on that?
I think sports watches are getting better and better when it comes to certain things. I like using them too and I feel like they help people who don’t like exercise and who need encouragement to be more active. But when it comes to parameters like VO₂ max, as a performance diagnostician and scientist, I always find it hard to take. Because it’s obviously only a very rough estimate. My last performance diagnostic measurement was 67 or 68. According to my Garmin watch, my value was 59. That’s no use to me.

Swiftly back to performance diagnostics then. Maximal oxygen uptake is the gross criterion for aerobic endurance performance. What would the net criterion be?
That would basically be what percentage of oxygen uptake I can sustain over a period of time. It’s no good if I have a super high oxygen uptake and only get 50 per cent of that over a long period of time. That’s why it’s not insignificant in endurance sports.

When energy can’t be provided aerobically, lactate levels rise and eventually performance can no longer be maintained. What role does lactate threshold play in relation to VO₂ max?
It would be an important additional variable. For example, the percentage of maximal oxygen uptake I can achieve at the 4 mmol/L lactate threshold. The term lactate threshold isn’t used that often anymore because it’s difficult to justify physiologically. Anchor points are more commonly mentioned now. The physiological gold standard would be to determine the maximal lactate steady state via a long-term test. This requires several 30-minute endurance tests at high intensity and determining when the lactate concentration increases by a maximum of one millimole.

So, the ramp test isn’t used.
Step test protocols are very common, starting with a low intensity and usually with stress levels of five minutes. When running, the speed is then increased by 0.4 or 0.5 metres per second. You have 30 seconds between the steps to determine the lactate concentration in the blood. These lactate concentration curves can then be used to derive different training zones. If you couple this with spirometry, which would be recommended, you can also see how many carbohydrates and fats are metabolised. This is another important piece of information because priorities shift depending on the running distance.
For short time periods, middle distances or long sprints, the glycolytic system is an important factor alongside the oxidative system.

Your research has often also involved the maximal lactate production rate. How is that related to VO₂ max?
It should indicate how efficient the glycolytic system is. Mathematically, we would expect the ratio of oxygen uptake to lactate production rate to explain the percentage exhaustion at peak lactate steady state. There should be a correlation that rises steeply at first and then flattens out a little. If we compare this with the measured values, we see very large deviations that can only be described to a limited extent using a model like this. That’s why we’re in the process of discussions and seeing if we have to consider other things. But we’re initially sceptical that it can work on its own, at least in terms of running. We’re working with colleagues to validate this in cycling.

So, when it comes to running, everything is a little more complicated.
Performance diagnostics are still important. But I’d be cautious about this mathematical model, which commercial providers also use for both cycling and running. Especially when something is simulated while running, it’s assumed that the mathematical assumptions apply. We’ve now done the measurements and maintain that they don’t. Maybe you can still derive a good training plan from this, but we don’t see any physiological connections.

There are so many different factors. How important is VO₂ max in cycling and running?
We always read that a high maximal oxygen uptake is the parameter in both disciplines. When cycling, the movement is relatively well managed, so VO₂ max really counts. Economy of movement and technical factors are less important. Although VO₂ max is by far the most important parameter in long-distance running, economy of movement still plays a major role.

How can the differences be identified?
The number of millilitres of oxygen required per kilogramme of body weight per kilometre travelled is extremely important. We normalise this onto the track to enable better comparisons. The lowest values I’ve ever seen in papers are around 160. That’s incredibly economical. Anything around 230 to 250 is very uneconomical. My running economy is 232, for example, so I’m very uneconomical. So, I have to compensate with a relatively high oxygen intake. These are the two most important parameters when running: first VO₂ max, then economy. This complexity always has a certain attraction for me. One has weaknesses, the other has advantages. That’s what makes watching running competitions so exciting.

Meet the expert

Dr Oliver Quittmann researches and teaches at the German Sport University Cologne, specialising in endurance sports. His studies involve various performance diagnostics methods, primarily examining the glycolytic metabolism. Alongside his work, the 31-year-old runs the video podcast «Exercise Inside Out» and shares his research results in science slams (both in German). He regularly publishes much of his teaching and research content on his YouTube channel (content in German).