Power Meters – why?

Let’s talk about bike mechanics.  Not how to fix your bike but a topic within the biomechanics of cycling.  Understanding biomechanics can help you understand why a power meter can be useful for training and racing.  Stick with me here, most of you probably do not want to revisit physics but it is not that complicated if you can give it a little time:

In order to finish a race we perform WORK.  In other words, it takes X amount of work to swim, bike and run a certain distance under certain conditions. 

To do the work required to finish a race, we have to produce power for the amount of time needed to finish.  In equation form then:

 Work = Power times Time

This is why the cycling industry invented power meters for cycling.  Power is directly related to to amount of work needed to complete a race.  It is important to point out that each race (and in fact, each date that race is run) the amount of work needed to finish changes.   Why? 

It takes more work to finish a race that has a head-wind compared to one that does not.  Just like it takes more work to finish a race that has significantly more hills. This is why some courses are slower than others.  And why some years on the same course are slower than previous years.  So this means, that it requires more power some days compared to others to go the same distance in the same amount of time. 

Our individual physiology determines how much power we can produce.  If we are putting out too much power too soon then we will fade later in the race because we exceeded our physical abilities.  So, in terms of how we can control our race, for the same amount of power (no matter what kind of day it is) it will just simply take more or less time to cover the same distance.  The time it takes then is largely dependent on the race day conditions.  For some reason athlete’s underestimate how largely race conditions can effect their time and substantiates the cause for using a power meter. 

Even more importantly…the amount of work needed to finish the race with the same finishing time is different for each athlete.  Body weight, body and bike aerodynamics, technique and so on will also effect how much work YOU need to do to finish the race in a set amount of time.  For example, since work is directly related to power, a lighter individual will climb a hill faster than a heavier athlete even though they are producing the same amount of power. 

There you go.  Now you have a clear cut way to measure your performance on any given day and it is all related to the amount of work you do and therefore the amount of power you exert.  Speedometers can not tell you this information since your speed is a function of the amount of power you produce AND the conditions you are overcoming (i.e. wind, road gradient, aerodynamics etc…).  We can measure the power but it is very difficult to measure wind speed and road gradients for example.  Plus, why measure more things when all we have to measure is power to get a simple measurement of our intensity.

How is this useful for training and racing?  Here is an incomplete list:

> Monitor performance improvements over time.

> Monitor fatigue.

> Set training zones using power levels.

> Help you to pace races better.

> Prevent you from over powering hills or corners.

> Test equipment changes or body positions on your bike.

 You might be thinking…Great, this is all I need.  This is a foolproof way to train and race.  We can define it all with mathematics and physics.  Unfortunately, it is not that simple.  We do have another large variable to consider when training and racing and that is your physiology.  Power is the outcome and is a good way to look at constraining training and racing but it is not perfect.  We are getting better and better at using power meters to help athletes but there will always need to be some individual control. 

Our brains our still the best computers around.  Months of training information is stored upstairs and you still need to use it no matter how good you get at using a power meter.  The power meter can not predict when you feel good, when you are sick, when you are low on fuel and so on.  Heart rate monitors to some extent can help solve some of those problems but they are not the perfect solution either.  We still need to tune into our breathing and our legs.  Our body is very good at telling us what is going on if we are willing to listen (are the muscles tight, sore, tired or do they feel normal or even great).  So, as far as I can see, it will always be a combination of physics, physiology and brain power which will help us to optimize training or race performance.

—Scott