Saturday, October 13, 2007

The Power Of Weight

"How many watts can you put out?"

Hardly seems like a question that you'd hear as a young kid. Certainly, not as common as "how many pull-ups can you do?" However, it is in the same vein. It is a measure of fitness. So, how many Watts can I put out?

As already discussed, you can measure power in Watts, and this can be measured by special instrumentation. However, raw wattage is not all that important in bicycling. Why not?

The answer is the same for athletes as it is for cars. A big engine in a light chassis means fast speed. A big engine in a big chassis means mediocre speed. So what you want is as big as engine as possible, with the least weight. (This is why I am currently dieting, but that is a story for my other blog.)

So, how would we use this information? The answer is as close as a race I did today. This morning, I did an 11 mile time trial. It was not flat, it was a lot of up hill. It took me 33 minutes to do the time trial, and I averaged 269 watts of power.

As mentioned before, Andy Coggan has done a lot of work on the theory of training with a bicycle power meter. In his work, he has defined a term called "functional power." Functional power is basically the power that you can hold for 1 hour. While, I did not go a full hour today, I can take my 33 minute time, drop it by about 7%, and I can get my functional power. This is about 250 watts.

However, I am a big guy carrying a fair amount of weight. Part of this is muscle, but a lot of it is fat. As a matter of fact, I think that I carry around roughly 40 lbs of fat! Every time that I pull that fat up a hill, it does nothing for me. The same athlete, with the same power plant, will be faster if they are lighter.

So, what is really important is the watts that you can put out per kilogram of weight.

So here are my vital stats:

Functional Power = 250 watts
Weight = 90 kg
Watts per kilogram = 2.78

Now, click on the table below. Look at the FT column and 2.77.



You can see that 2.77 is about right in the middle of the Category 5 Racers. If you care serious about bike racing, you'll do some training and the first category you will race in is Cat 5. Now, lets say that by some miracle, I could lose 22 lbs of fat (and I would still have 18 lbs left!), I could move one entire category up.



Another way to look at Andy's table is the above graph. What I've done is take the numbers in the first chart and graph them. Every category has a different color. The different category of bicycle racers are roughly the same length. The graph here shows that you see a steady increase in power as the success of the rider goes up.

Now lets say that I could lose a bunch of weight, but keep the same power out. The following chart shows what my weight would need to be at 250W worth of Functional Power.

If you've ever looked at the upper echelons of bicyclists, they are all legs, and super lean. They will be 6 foot and 140 to 150 lbs of weight. In the following chart, I have graphed my needed weight @ 250W for me to get to higher categories of performance.



If I was built like some professional bicyclists, I would only weight 150 lbs. I have shown this on the chart. However, even at 150 lbs, I am not putting out enough power to get beyond a Cat 3. So, while I'm in okay shape, I would need to do more than lose weight to get above a Cat 3 racer.

Therefore, it should be clear from the data, that just decreasing your weight is not enough. You also need to be powerful. However, as you probably know from experience, a powerful rider with a lot of body fat will also do poorly.

Now, in bicycle time trialling, there are two types of races: flat and hilly. As the bicycle course becomes more and more hilly, the power per kilogram becomes more and more important. When you are on the flat, carrying a few pounds isn't noticeable. However, if you are climbing a lot, the extra weight becomes very important.

However, at the upper ends of performance, you need everything going for you. You need to be lean and powerful. But even us mortal and older bicyclists need to understand that for optimum performance, we can also improve both by power and weight.

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