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

this we can say that work is force multiplied by distance. As a formula it looks like this:
W = F × d
    Now, knowing what work is, if we go back to the first formula (P = W/t) and substitute force times distance (F × d) for work (W), since they mean the same thing, we get another way of expressing power:
P = F × d/t
    This formula says that power results from force (you lifting the barbell) multiplied by distance (how far you moved the barbell) divided by time (how long it took you to stand up). For example, if you add more weight to the barbell and do another squat standing up (F) to the same height as before (d) and in the same amount of time as before (t), you’ve increased the power generated. That’s because force was increased. Or you could keep the weight on the barbell the same as before and stand up (F) to the same height (d), only faster (t). That would also increase the powerbecause time decreased. Thus, power results from the interplay of force, distance, and time.
    Still with me? If so, let’s see if we can simplify this even more.
    You know that distance divided by time is called “velocity,” which is what we more commonly call “speed.” In your car you talk about speed as miles per hour. That’s distance (miles) divided by (per) hours (time). So if velocity (v) is the same thing as distance divided by time (d/t), we can substitute v for d/t in the last formula, giving us an even simpler way of expressing power, especially when it comes to riding a bike:
P = F × v
    This is the final formula: Power equals force times velocity. It’s where I wanted to take you with this somewhat roundabout way of understanding power from the perspective of physics. In bike riding, force and velocity are easier to understand than work divided by time, which is where we started. On a bike, force is what you put into the pedals and velocity is how fast you are turning the pedals. So now that we have the hard part out of the way, let’s move on to how power is produced through the interplay of force and velocity when you ride a bike.
Power in Cycling
    When you are pedaling a bicycle, force and velocity are always present and determine how much power you are creating. As you push down on the pedal, you’re applying a force (F). The harder you push, the more force you are applying and therefore the greater is the power you produce. (In physics this turning force applied to the rotating pedals is called “torque.” That’s not too important for your understanding of power, but you may run across this word in your power meter software.)
    When you are pedaling your bike, the rotating-pedal equivalent of velocity is called “revolutions per minute,” or “RPM.” That’s a term with which you’re already familiar. You may also call it “cadence.” As RPM, or cadence, increases—in other words, as you pedal faster—power is potentially increasing. I said potentially because the increase depends on whether you changed gears or not. Pedaling at a higher cadence in the same gear produces more watts because pedal velocity (v) has increased.
    All of this means that in order to raise your power while riding, you can either increase the force (F) you apply to the pedals or you can increase the cadence (v). In the real world of riding a bike, the way to increase the force is to shift to a higher gear and keep the cadence the same. For example, you could shift from 53×17 to 53×16 while maintaining your cadence. Force will have to increase for this to happen (you’ll have to pedal harder). That will increase your power output, which in turn will increase your bike’s speed. Or you could keep the force the same by not shifting gears and instead increase your cadence by turning the pedals faster—for example, by going from 85 RPM to 90 RPM. This decreases the time it takes to do the work, thus increasing power.
HOW A POWER METER WORKS
    So force and cadence are what your power meter is detecting. Calculating the cadence part is easy. The meter simply measures how long it takes for the cranks to make one full revolution. Some power meters do this by having you place a magnet on a crank arm and a magnetic sensor on the frame. Others do it by electronically detecting the sine wave you produce as the cranks go around and then measuring the length of one wave to determine cadence. Force (actually, it’s torque that’s measured) is a bit trickier to compute.
    To calculate force, your power meter has something called a