Admittedly, this topic might seem quite trivial. But let’s keep in mind that there are some people among us who don’t really know what a cycling power meter is - or have only a vague idea. The next few posts will comprise a mini-series, revolving around power meters. To make sure we don’t lose anyone early on, this post is committed to explaining what power is, how a cycling power meter measures it, and what it's all good for.
What exactly is "Power"?
In a physical sense power is the rate of doing work. “Work” usually has to do with a force, causing a displacement (Work = Force x Distance). Power is the rate (speed) at which this displacement occurs. Let’s say you are at the grocery store and you are picking up two six packs of beer, lifting them into your shopping card. This requires work (force applied over a distance). Now, let’s say you are lifting each pack at a different speed. Although. each time, you are lifting the exact same weight, the exact same distance, requiring the exact same work, doing it faster leads to a higher power rating.
Power = Work / Time
Here is another example: you are riding your bike for one kilometer, using the exact same gear, and going the exact same course, under identical conditions. The first time you do it in 1min, the other time you do it in 2min. Each time you are doing the same work, expending the same amount of energy, but your average power will be different. The 1min trial will end up with a power rating twice as big as the 2min trial.
In short, power is the rate at which (how fast) you are doing work.
How does a cycling power meter measure that?
Most power meters use so-called strain gauges to measure the force you apply to the drive train. For example, a crank-based power meter has strain gauge(s) in the crank arm, which measure how much “strain” you are causing to it, in other words, how much you are bending the crank arm (on a microscopic level) while pedaling. The distance required to turn the crank arm one full revolution is the distance over which you are applying the force. This (force x distance) is the work you are doing. Now, the time in which you are doing the work, hence in which you are completing the pedal stroke (measure as your cadence) allows computing the power. The unit your power is measured in is usually Watts.
Why is that good to know how much Watts I am expelling when exercising?
Using above example: as you can imagine, the effects the two different trials have on your body, would be different. If you understand that, you also see how power is a good way of measuring exercise intensity. Measuring and gauging exercise intensity, in turn, is a key component in any goal-oriented and event-specific training regimen.
Many other metrics are used to measure and gauge exercise intensity: heart rate, pace/speed, rate of perceived exertion, oxygen consumption, blood lactate levels, and more. The problem is many metrics are either difficult to access (at least in the field), represent only an indirect measure of the intensity you are exercising at, or can easily be influenced by outside factors. Power (Watts) is a much more objective measure of exercise intensity and also lets you quantify the work load of your training. This can be used as a measure of the total training stress and, therefore, as a measure of what kind of fitness gains you can expect from your training.
In the next posts we will explore in detail what you can do with a power meter, if you really need one, and which one of the many choices would make sense for you.
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