Thursday, 7 August 2008

Fast or Slow... The decision is yours.

A few years ago I bought a trip computer for my bike. I think that I was about to embark on a trip up North and so wanted to keep a note of my mileage and speed. I also wanted something I could use on my turbo trainer so I could see how far I had gone without going anywhere. It has the basic functions like speed, average speed, max. speed, odometer, etc. One thing I had never used though until recently was the cadence function. But what is cadence and why is it so important to a cyclist? Put simply, it's a measure of the number of revolutions your pedals do in a minute. The reason this is so important to cyclists will become clear as I go on.

Supposing you had two cyclists of equal size, on the same type of bike, travelling along the same road at the same speed at the same time. Now, imagine that Cyclist A has a cadence of 70 rpm and Cyclist B of just 50 rpm. Who is doing the most work in moving their bike along the road? The laws of Physics dictate that the power required to move a bike is equal to the force exerted on the pedals multiplied by the cadence (Power = Force x Cadence). Therefore, if each cyclist has the same power output, Cyclist A would be required to put less effort into pedalling his bike, even though he is pedalling faster than Cyclist B.

Now, I don't pretend to understand all the Physiology of this but it goes something like this. Your muscles are made up from two different types of fibres; Slow Twitch and Fast Twitch. Slow Twitch fibres are more efficient at using Oxygen to generate fuel and are very resistant to fatigue. They are used to provide sustained power over long periods of time. Fast Twitch fibres on the other hand burn glycogen which is stored in the muscles themselves. This means that they tire very quickly and take a lot longer to recover. The advantage of this however, is that they are much better at generating short bursts of power.

Professional cyclists tend to use a cadence of around 90rpm and higher. Lance Armstrong apparently used to train at 120 rpm for long periods of time. When he hit the mountains in the Tour de France he dropped down a few gears and then upped his cadence while others preferred to get out of the saddle and power their way up. The other day I went out and tried to keep a steady cadence of around 80 rpm. To be honest, after a time my knee and hip joints began to hurt a little but I didn't feel as tired after 10 miles as I perhaps normally would. It also felt slightly unnatural pedalling that fast.

So what is the optimum cadence? Well, there are no doubt many trains of thought on this but from what I've been able to find out it depends on the terrain. In general though you should aim for a cadence of between 85 and 93 rpm.

1 comment:

Mauro Masucci said...

There is also a third type of muscle which is a mixture of the fast twitch and slow twitch muscles. Only one organ in the body is made from it. Your heart. It has the ability to function in the same way as Fast twitch fibres but without the lactic acid build up!