Beginners Guide To Power Zones - 4 Why Power Is Important

The starting assumption of this article is that a rider wants to get fitter. But what, exactly, does being “fitter” mean if you are a cyclist.

It is quite simple.

Being fit is the capacity, over time, to generate energy and transfer it to the bike. The more energy you can produce and the longer you can do it then the fitter you are.
True, there is more to being fit such as the ability to recover from and repeat hard efforts together with being able to generate energy efficiently, so conserving limited fuel.

And being the fittest will not necessarily make you the fastest. Turning fitness into actual speed means dealing with the factors that make you slower (aerodynamic drag, force of gravity, rolling resistance and drivetrain efficiency).

And the fastest rider will not always win . Converting speed into a place on the podium requires mastery of other factors such as pacing, nutrition, bike handling and tactics.

Still the need to produce energy and keep producing it at as high a level as possible is fundamental if riding a bike in pursuit of a performance related goal. All other things being equal then the rider that can do this best will win. (A top professional cyclist, for example, can produce more than twice as much energy per hour compared to an average cyclist of the same weight and consequently will always ride much faster for further.)
“Energy over time” is more succinctly called “power” by physicists who measure it in “watts” (or “W”), with “wattage” being a term to denote the power of a device or engine.
Cycling borrows these terms and puts them into practical effect by means of the power meter. So when a cyclist rides at 100W they are generating enough energy to keep a lightbulb with a wattage of 100 bright. (For a more extreme example search for “cyclist vs toaster”)

Power meters come in a variety of types but most measure two key values:

• The force applied to the pedals. More specifically the aspect of the force that causes rotation or ”torque”.
  
• The speed at which torque is applied. (Most power meters are attached to the crank so they simply measure cadence which, combined with crank length allows this value to be calculated)
  

Multiplying these two results in power. Cyclists have always known that if you want to go faster you push down on the pedals harder, spin them quicker or, ideally, do both at the same time. All that power meters do is measure this and produce a standard number of the result.

Power is produced by our muscles and so those with more muscles tend to produce more power. However extra size and weight means aerodynamic drag and gradients will slow these riders down more. Broadly speaking these two effects cancel each other out. So, when comparing riders, wattages are sometimes expressed as a power : weight ratio (W/kg).

What makes power special as a measure, compared with say your speed or heart rate is that it is a universal currency. If you know someone can average 25mph on a ride with an average HR of 140bpm you really cannot make any judgement about how fit they are. On the other hand knowing a cyclist can average 400W for an hour, regardless of whether this is on a Wattbike at the gym, up a mountain climb or in a long time trial instantly lets a coach know that they are pretty good, especially if that equates to over 6W/kg.

This is not to devalue other measures such as speed, heart rate and RPE. They are important and can become even more so when combined with power measures. For example a TTer seeking to improve their aerodynamics or testing equipment options will be interested in anything that increases speed while keeping power constant and/or seeing if a more comfortable position that produces more power can be achieved without sacrificing speed. For all riders a fundamental measure of improving fitness is that you can do more with less effort. Seeing power go up while HR and RPE stay the same is one sure sign your training is working.