The Power Meter Handbook: A User’s Guide for Cyclists and Triathletes

“strain gauge” built in. This is the single most expensive part of a power meter and accounts for much of the price you paid for yours. It’s found in the cranks, bottom bracket, rear hub, or pedals, depending on which type of power meter you have. There are generally several strain gauges in a power device to make the reading more precise. Good power meters are generally accurate to within plus or minus 2 percent.
    A strain gauge is a thin, flexible strip of material with a metallic foil pattern inlaid on it. As force (torque) is increased on the pedal, the strain gauge is very slightly stretched, thus changing the shape of the metallic foil pattern. When the pattern deforms, its electrical resistance changes. The amount of this change is an indication of how much force (torque) is being applied.
    So that brings us back to P = F × v. Now that the power meter knows force and velocity, it can determine how much power (watts) you’re creating and display that on your handlebar computer. Simple, huh?
GETTING FITTER AND FASTER WITH POWER
    So if power is force times velocity (P = F × v), what can you do to build more force or increase your pedaling velocity (cadence)—or both? Powerful cyclists typically do both. When necessary for performance, they can select a high gear and pedal with a high cadence. For example, a pro road cyclist who specializes in sprinting can shift to the 53-tooth chain ring and the 11-tooth cog and still turn the pedals at 105–115 RPM. This produces very high power output, often around 1,500 to 1,800 watts. That’s why these cyclists sprint so fast. Most recreational riders sprint at about 600 to 1,000 watts using a much lower gear and cadence. On the endurance side, a pro triathlete in an Ironman may select a 53 ring and a 14 or16 cog witha cadence of 85–90 RPM and average around 290 watts for four and a half hours. Even though the actual numbers vary, the best athletes are capable of using both a high gear and a high cadence. More than likely you’re not at such levels—yet!
    Let’s take a 30,000-foot view of what it will take to get there, or at least to some higher level of power than you currently are able to produce. We’ll examine both force and cadence improvements. Later, in Part III , in the chapter focused on your sport, we’ll take a closer look at the specifics of what you can do to train more effectively to improve power so that you become fitter and faster. There I will explain the details for merging the power of physics as explained above with the physiology of training as I’ve previously described it in my books The Cyclist’s Training Bible, The Triathlete’s Training Bible, and The Mountain Biker’s Training Bible.
Force
    For most of the athletes I’ve coached over the years, force is the key to greater power. They’ve needed more “aerobically active” muscle. These are primarily the slow-twitch, or type 1, muscle fibers you’ve probably read about before. Slow-twitch muscles are the ones that improve your endurance. They are not very powerful—certainly not as powerful as the type 2, or fast-twitch, muscles—yet they can contract many times before fatiguing. You have both types throughout your body, with their ratio depending mostly on genetics. Good endurance athletes have an abundance of type 1, whereas sprinters have lots of type 2. Type 2 muscles, while quite powerful, fatigue very quickly. They’re great for sprinting since they can contract many times faster than type 1, but they aren’t very good for endurance riding.
    There are two subtypes within type 2, called “2a” and “2x.” The 2a fibers have some of the same characteristics of type 1, yet they are primarilyfast twitch. The 2x muscles (they used to be called “2b”) have the potential to become more like 2a, meaning that their endurance qualities can be improved. With proper training, your fast-twitch muscle fibers, which are already good at producing force, can become more endurance oriented, while your slow-twitch fibers can become better at generating force. The result of all of this physiology babble is that a good training program will help you produce more force and therefore more power, as I’ll describe in Part III .
Cadence
    Pedaling in a very high gear with a very low cadence is not only a poor way to produce power; it is also quite inefficient. That’s how those new to cycling sports usually start out. They bog down by mashing gears in the big chain ring and