The Power Meter Handbook: A User’s Guide for Cyclists and Triathletes by Joe Friel Read Free Book Online

normalize the power of several riders for their weights (and, in fact, we will do so in a later chapter). To do this, we divide power by body weight. For example, if rider A weighs 180 pounds and his average power for a given ride was 210 watts, his power normalized for weight would be 1.17 watts per pound (210 ÷ 180 = 1.17). We could compare that with rider B’s data on the same course. If B weighs 120 pounds and had an average power of 150 watts, her power normalized for weight would be 1.25 (150 ÷ 120 = 1.25). So we could conclude that even though A puts out far more average power than B, B is actually more powerful pound for pound. That relationship becomes very important under some circumstances, such as climbing a hill, which we’ll get to later. But for now, that’s what is meant by normalizing.
    NP compares the range of variability of power during a ride with the average power of the ride. So when you see the word “normalized,” you are being tipped off that we have altered the parameters to be examined. Let’s see if we can get a better grip on this concept.
    If you’ve had a chance to download and look at one of your power charts from a ride, you certainly will have noticed that there are lots of spikes in the chart. If you compare the power chart with the heart rate chart for the same ride, you’ll see that heart rate doesn’t spike nearly asmuch. That’s because power generation is quite variable and the power meter is very sensitive to change, whereas heart rate doesn’t change much at all. If you were a machine, we could design you to create steady, even power. But you aren’t a machine; you’re human, and humans expend energy with lots of high and low spikes. Every time there is a rising spike in power, you are expending more energy than if you rode with perfect steadiness and no spike at all. Average power doesn’t account for these minute changes in power and therefore in the energy you used to pedal. Normalized Power does.
    The concept of Normalized Power is critical for power meter training because it reveals the true effort of a ride by accounting for variability. I will refer to NP frequently throughout the following chapters; to help lock it in, let me give you a real-life example of NP from two of my recent rides.
    Not too long ago, I had only 1 hour to work out between other commitments. You know how it is sometimes—you have to shoehorn bike rides in whenever you can by working around other responsibilities. I happen to live at the top of a 1-mile hill that is about a 5 percent grade. What I did for this short workout was repeats on the hill for 1 hour. On the climbs I rode at a hard effort with several short surges thrown in all the way to the top. Once at the crest, I turned around and coasted back down without pedaling. After 1 hour my average power was 141 watts. The next day I was a bit tired from the hard workout the day before, so I went for a moderate-effort, steady ride on a flat course. Interestingly, my average power was once again 141 watts. Now, there was nothing about those two workouts that was even remotely the same except for the average power. I burned a lot more calories per hour climbing and descending the hill than I did riding steadily. In fact, NP reflected this difference. The hill-climbing workout had an NP of 176 watts. For the moderate-effort ride, it was 149 watts. If I had only the averagepowers to compare, I would assume the effort and the metabolic cost were the same for both rides. They obviously weren’t, and NP revealed this.
    So what NP is actually telling us is what the workout felt like, which is a much more revealing training component than a simple measurement of average power level for the ride. In my example, the hill repeats felt much harder than the steady, moderate-effort ride, and NP reflected a difference that average power would not. Normalized Power also gives us a much better idea of the energy cost of a ride. Doing surges on the hill