Taking it to the VO2 max with Cycling Physiology
Meera - We've had an insight into the role engineering can play in producing faster, stronger bikes, but what about the strength and speed of the person on the bike, the cyclist? Cyclists on the Tour de France cover between 150 and 200 kilometres every day, for three weeks, with only two rest days in between. This requires an extreme level of stamina and endurance. So to find out how the physiology required to meet this endurance level can be monitored, and improved upon, when I got back, I met sports physiologists, Fergal Grace and Adrian Elliot in their sports science lab at Kingston University, and took Naked Scientists Julia Graham along for some testing.
Fergal - Well first of all, for cyclists, we're looking at their aerobic fitness, which is key to being a top quality performance cyclist. Other things we look at are muscle power. You'll have two different types of cyclists - you'll have the climbers and the sprinters. They've got fundamentally different muscle fibre types. So the sprinters can generate a lot of power very quickly whilst climbers have got a sustained, controlled release of power.
Meera - So, we're currently in your lab here at Kingston at the moment, where Naked Scientist Julia Graham is currently undergoing a VO2 max test. So this is obviously monitoring oxygen, but what does this test involve with regards to oxygen uptake?
Fergal - We know how much oxygen is in the atmosphere. If we can measure accurately, expired ventilation - which is when somebody breathes out during exercise, the difference between the atmospheric air and the air that's expired out, is being consumed by the body. The more aerobically fit somebody is, the more oxygen they can utilise per kilo of body mass. That's fundamentally what this test measures.
Meera - Julia is currently on a Veletron, which is an indoor bike. She's wired up to all sorts of computers. You're the one here testing her and monitoring her. What are you actually looking at when she's on this?
Adrian - At the moment, we can see the amount of oxygen that Julia is consuming per minute. We can see that relative to her body mass, which gives us a good indication and allows us to compare Julia's values to those achieved by individuals of other sizes, whether they are elite athletes or cardiovascular patients.
Meera - And what are the measurements at the moment?
Adrian - At the moment, we see VO2, which is oxygen consumed at roughly about 30 millilitres per kilogram, of Julia's body mass, per minute. We'd expect that to rise in a healthy, sedentary individual to values perhaps in the 40s. The more trained an individual becomes, and perhaps the more genetically predisposed towards aerobic exercise they are, we should see values in excess of 60, 70, perhaps even 80 millilitres per kilogram per minute.
Meera - And how much can someone then train, to actually say, almost double that then?
Adrian - Well they can participate in prolonged aerobic exercise. Perhaps some elite endurance athletes would be training for 2, 3, 4 hours a day, trying to look at using the heart and lungs to bring in oxygen, and encourage the muscle cells to actively use that oxygen.
Meera - And how useful would you say that this test is then, for pro-cyclists to be aware of their VO2 max?
Adrian - It's very useful. It allows them to see their total capacity. So aerobic capacity, the maximum amount of oxygen they can use at sea level, at the moment. What we can also see from the data we're getting in these tests is something called anaerobic thresholds, which will tell us the intensity at which an individual can sustain exercise for extended periods of time, in excess of perhaps 20, 30 minutes.
Meera - I guess that is crucial because at the moment Julia will be on this bike for about 10 minutes say. She's not always - if she was to go for hours - going to be at the same peak performance, is she?
Adrian - No. Absolutely, not. The values that she achieves at the high intensity stages wouldn't be sustainable for a long period of time. Perhaps what becomes more interesting is the more we can look at Julia, the more we can see what kind of exercise level she can sustain. So she may keep the same total capacity, but if she can train to the point where she can work at a higher intensity, so a higher percentage of that aerobic capacity, then that will come with benefits in terms of performance times, and perhaps placings in an event.
Meera - Now Julia, you've been going for 30 minutes on this test. How are you feeling?
Julia - I'm pretty out of breath...
Meera - How has the resistance been, or how has it generally felt throughout though?
Julia - It goes up each time, so by the end it was really tough and I'm pretty knackered.
Meera - But initially, so when you first started, were you okay at a steady pace?
Julia - Initially, it was really easy and I thought I can do this real easily, and then it gets much harder as you go along. Pretty knackered.
Meera - Well Adrian, what are Julia's results now?
Adrian - Julia reached a VO2 max, that's the maximum oxygen consumed, of 45 millilitres per kilogram, per minute. So, it's in the range that we would associate with an active, sedentary, but healthy individual. If Julia were to now engage in some aerobic training, perhaps train for a long event, we'd anticipate that her VO4 would rise up into the 50s, perhaps 55 would be a realistic target for Julia at this stage.
Meera - So, well done Julia.
Julia - Thanks very much.
Meera - Now Fergal, what's actually going on inside someone's body then to affect this capacity and this uptake.
Fergal - If we look at this, just from the outside, it looks like it's very much breathing, or respiratory based, or based around your lungs. In actual fact, the major changes that are happening are with the heart. The heart is going to become more elastic, going to fill with more blood, and is going to pump that blood around the body. Now what happens with an endurance training program, is that the chambers inside the heart become larger. And in doing so, they're able to hold more blood, and when it contracts, are able to force more blood around the body, so that the body becomes more efficient at pumping oxygenated blood around the body.
Meera - What are other tests that you also perform in the lab, to assess other factors, as well as VO2 max?
Fergal - Some of the factors we'd look at would be metabolic, and the one that immediately springs to mind, is a lactate threshold test, whereby, another incremental test is done on a number of occasions, and lactate samples are taken at the end of each stage. Lactate is a toxic metabolite in the body, formed from the breakdown of carbohydrates. When it builds up in the muscles, it creates fatigue. Once somebody becomes more efficient at exercise, you can delay the onset of that accumulation of lactate. That's why cyclists would be interested in coming in to have a lactate profile test done, and on the basis of that, they can work out how hard they're going to exercise during their training sessions. They're going to want to exercise on, or about, their lactate threshold. So that is the point at which you're exercising at approximately 70 to 75% of your maximum ability, and the lactate starts to appear in the bloodstream.
Meera - A last factor then Adrian, is the fact that a lot of cyclists also, as well as monitoring their oxygen uptake, also look at how much power they're actually producing when they're cycling?
Adrian - Yes. Well we've measured power here. Julia reached a value of 170 watts which equates to around about 3 watts per kilogram, for body mass. In cycling, power to weight ratio is the key for most of the performance. In a pro-cyclist, for instance, in the stage in the Col du Tourmalet, leaders were reaching values reported to be just under 6 watts per kilogram, which is an extraordinary amount, even for the most trained individuals. We rarely see values such as that, and they're sustaining those levels over an extended period of time, perhaps 30, 40 minutes for the duration of a climb.
Meera - How would you summarize then, the key factors that are crucial to someone coming in and knowing what they need to make them a good procyclist?
Adrian - If we were to prioritise, we'd look at - as we've done today, aerobic capacity, and anaerobic threshold. We'd also be very interested in efficiency of an individual, so perhaps looking at their oxygen consumed per unit of work, or how much of the energy they produce goes into actually moving forward, keeping a low body mass, and a low upper body surface area. Together, those factors are probably the major determinants of cycling performance, particularly at the professional level.
Meera - So, although many of us could train to improve our endurance, there are a rare group of humans out there that are actually able to perform at the levels that the pro-cyclists do. So it comes down to genetics in the end. That was Adrian Elliott and Fergal Grace from the School of Sports and Exercise Science at Kingston University.