Friday, February 1, 2013

What is Power Exactly?

Since I'm focusing on metrics lately, I figure it is probably important to discuss what power actually is, since many athletes may not really understand it.

If you’re reading this blog, it’s likely because you have purchased a power meter and want to know how to use it to maximize your training. One of the biggest things you’re probably wondering is, “What is power exactly?” and “How does the power meter actually calculate it?”

Remember that HR is an input metric? Power is an output metric, and one of the most important output metrics there is for training.  Power is a work rate, measured in watts. Work is the basis here, and it is important to understand the actual work being done is the movement of your body and bike.

When you apply a force to the bike through the pedals and crank arms, the bike moves you. If you apply a force and don’t move, no work has actually been done. In other words, force times distance equals work. We can express this with the following equation where Work is W, Force is F, and D is distance:

W = F x D

We know that Power is a work rate, so the equation for work simply needs to be divided by time to be a rate. This gives us:

P = (F x D)/T

If you think back to all the story problems you did in elementary school, you know that distance is equal to rate of speed, or velocity, times the time you travel at that speed, or:

D = V x T

Now comes the algebra you have always wondered if you would ever actually use in your lifetime outside of school. We will substitute this equation for D into the Work equation:

P = [F x (V x T)]/T

Now we have Time on the top and bottom of the fraction, which allows them to cancel each other out. This leaves us with:

P = [F x (V)]

And this leaves us with our basic equation to define power:

P = F x V

In basic terms, this means power is equal to the force you apply, times the speed at which you apply it. When riding our bike, this means how hard you press on the pedals, and how fast you turn the pedals. Power meters measure or estimate the force we apply, based on the brand and model you use, and then simply use the cadence value to multiple and get the work rate.

The more fit the athlete, the higher the work rate they can produce, or the more efficiently they can produce a certain work rate, (watts). 

Coach Vance

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