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Saturday, July 28, 2007

Success at cycling in the mountains: Apart from drugs, what does it take?

I guess the title of this post is hypothetical, because from the developments over the last week and a half, it seems that prerequisite number one is to have the right pharmaceutical support. But we will attempt to refrain from further jabs at the sport. However, as I write this, at 10:21 on Saturday morning, the word coming out of France is that another prominent rider has tested positive, and there is speculation that it is a Barloworld rider - any bets for Soler Hernandez? So this might be one of our more hollow posts, but we thought we'd have a look at the PHYSIOLOGICAL characteristics of elite cyclists, based on testing that has been carried out over the last 10 years. Obviously, the requirements are dependent on the type of rider and the type of stage being ridden. Tom Boonen, then, is a very different rider to Alberto Contador, and a time-trial requires a very different "skill-set" to a mountain climb. So the table below shows some of the requirements of flat stages, mountain finishes and Time-Trials. This is adapted from a research paper from Lucia et al. (2003).

We'll focus primarily on the mountains for this post (apologies to sprinters and Time-trial specialists)

Power to weight ratios

Climbing success is all about power to weight ratios. In order to climb at the front of the peloton, the required power output is approximately 6W/kg. Therefore, a 60kg likeweight needs to be able to produce a power output of 360W for upwards of 45 minutes, whereas a slightly heavier rider weighing in at 75kg must maintain 450W for this time. It's easy to see then, why guys like Pantani, Hamilton and even Armstrong (post-cancer) were more successful in the mountains, and also why Ullrich, who famously struggled with his weight between Tours, would face such an uphill (excuse the pun) battle during the Alps and Pyrenees of the Tour.

Incidentally, on the note of Armstrong, Ed Coyle published a study in 2005 in which he reported Armstrong's power outputs, VO2 values and body weights over a period of 7 years between 1992 and 1999. This paper was widely criticized, for reasons not worth going into here, but it did show the following numbers, which demonstrate the point about power to weight ratio:

Armstrong's weight in 1992 = 78.9 kg
Power output when cycling at a VO2 of 5L/min = 374 W

Armstrong's weight in 1999 = 72 kg
Power output when cycling at a VO2 of 5L/min = 403 W

So the increase in power output when cycling at the SAME level of oxygen consumption was 29 W. However, what is more significant was that his weight came down by 7 kg at the same time. This meant the following for power to weight ratio:

Power to weight ratio in 1992 = 4.74 W/kg
Power to weight ratio in 1999 = 5.60 W/kg

This is an 18% improvement, which is massive. It means that Armstrong's change in body mass and slight increase in power output add up to a huge increase in climbing performance. The other contributor to this change, by the way, is increased cycling efficiency, because when cycling at the SAME VO2, Armstrong was able to produce a greater power output, and that's important for a number of other reasons, one of which we'll get to in a moment.

So, all the top climbers in the Tour de France are able to ride at about 6 W/kg for 45 minutes at a time. This obviously does not account for the ability to accelerate and open gaps on competitors, which would require power outputs of 8 to 10 W/kg for a short time! So an attack might see a rider lift the power output up to 600 to 800W for a short time, then settle back into a level that they can sustain for the next 45 minutes!

What's the deal with VO2max? And the importance of efficiency...

Another factor that gets a lot of air-time is VO2max. Basically, this refers to the volume of oxygen that the athlete can use at maximum effort or exhaustion. Personally, we don't think it's all that vital - just have a look at the paper of Lucia (Med Sci Sports Exerc, 2002) which showed that the best cyclists did not necessarily have the highest VO2max values. Of course, if you are going to be a world-class cyclist, its almost a given that you have to have a high ability to use oxygen, but once you get there, then it becomes a little different. In otherwords, a world class athlete will have a VO2 max of anything between 70 and 90ml O2/kg/min. But the guy with 90 is not necessarily better than the guy with 70!

Why is this? Two reasons. The first is that cyclists in the Tour are not riding at VO2max when they compete anyway - they are, as the table shows, only at about 80 to 90%. Therefore, it is not "top-speed" that counts, but economy at submaximal intensity. A rider who is economical will be able to ride at 80% of his VO2 for longer than a rider who is not, and so VO2max becomes less important.

Lucia showed it in that paper from MSSE (2002) , where he found that the guys with the high VO2 tended to have a lower cycling efficiencies. Looked at the other way around, a cyclist with a lower VO2 will have a higher efficiency of cycling.

What does this mean? Well, cycling is an efficient activity, but it's far from perfect. Remember your high school science when you may have learned about steam trains and the fact that a lot of energy from the coal gets lost as heat. Similar to cycling. So a cyclist is actually doing a lot more work than what actually goes into moving him and his bike forward. Generally, people will have efficiencies of between 15 and 25%. This means that only 20% of the energy you put in actually contributes useful work.

The implications of this are enormous - it means that a cyclist who is 20% efficient might be riding at 400 W, but he's actually producing 2000 W of work (20% of 2000W is 400W). Now, if this same cyclist could increase efficiency by just 1%, then he would be able to ride at the same power output of 2000 W, but his USEFUL work would jump up to 420 W (21% of 2000W). This 20W difference is, as I'm sure you can imagine, massive.

So the take-home message of all this is that it's not so much what the rider can do at MAX, but how efficient he/she is at sub-maximal levels, and this involved efficiency.

Obviously, there are many more factors that have to be present to allow elite cyclists to ride the way they do - ability to use fat as energy, metabolism, ability to clear lactate, lung volumes, heart function etc. But that is a book, not a blog post, which we can perhaps get to some day!

For now, though, the key is the ability to sustain a high power output for long periods, and to ride with maximum possible efficiency!

Oh, and then having some drugs seems to help too...

2 Comments:

Colenso said...

You make an excellent point about the relative irrelevance of VO2max to competition outcome.

I should like to emphasise here a point that rarely seems to get addressed in the popular literature. This is that VO2max figures are not absolute values. Rather, they are what we call in physics specific values: that is, the absolute value divided by the mass of the system under observation.

Hence, to take a 60kg adult male elite endurance athlete as an example, if he has a calculated V02max of 80ml/kg/min, that value has been calculated by dividing his total maximum oxygen consumption per minute measured on the treadmill or on the ergometer by his body mass of 60 kg.

So to have a VO2 max of 80ml/kg/min it follows that his total max O2 consumption must have been measured as being 60 kg x 80ml/kg/min or 4800ml/min or 4.8 l/min.

What's the upshot of this? Well, the easiest way for most recreational athletes to boost their calculated V02max figure (if that's important to them) is usually to lose some weight!

Ross Tucker and Jonathan Dugas said...

Hi Colenso,

It is great to have a basic scientist contribute to the discussion here. As Ross mentioned, we are a young profession and often times do not attract professionals who have solid training in the basic sciences. The result is what you saw---the misuse of key terms and concepts.

You are mostly correct when you talk about relative VO2 measurements in that many athletes see losing a few kg's as a great way to change their VO2max.

However, their bigger mistake is that VO2max is not that strong of a predictor of performance, and so just by changing it a few mL/kg won't always translate into a faster 10 km or marathon time.

We take the relative value probably for the same reasons as you might in physics. It allows us to compare that variable between different individuals. The problem is that a 100 kg person might have a VO2max of 5 L per minute, while a scrawny little endurance runner might have a VO2max of 4-4.5 L per minute. We both know that the little guy is likely the better endurance athlete, and dividing his absolute VO2max by his mass confirms this for us.

Thanks again for contributing!

Kind Regards,
Jonathan