These power metrics could potentially unlock how you train and race—and eventually become a better triathlete
Photo by Don Velasco
Power meters are so common now that it’s easy to forget how scarce they were just a decade ago.
When I got my first power meter sometime in 2010, it was so expensive that it cost almost as much as my entry-level road bike. It was also so uncommon at the time that you could barely find one on the road. Back then, training centered on power and data was also somewhat unpopular with coaches and athletes that it’s easy to look past it and buy bling aero wheels instead.
I saw things differently though. I was willing to invest in an expensive piece of equipment since I came from a computer and data-based background. I knew that by quantifying my efforts in training, I could learn more about my body and push it to its limits.
And truth be told, the single most important thing that contributed to my racing success was using a power meter.
These days, it’s pretty easy to find a cheap power meter for a quarter of the price it cost a decade ago. It’s so ubiquitous that a lot of people forget how much engineering and precision it takes to produce one of these devices.
Moreover, a lot of people underutilize the data we get from these devices and in effect, treat them as expensive speedometers: a passive way to record effort rather than an active way of influencing training. With this in mind, let me share some power metrics that could potentially unlock how you train and race.
It’s normal to stop pedaling when you ride outside. This is an inherent part of cycling, but it largely affects the average power we produce during a ride. For example, compare these two efforts: 150w at 10 minutes and 300w for 5 minutes followed by 5 minutes of not pedaling. Which one feels more difficult? The latter, right?
However, from a data standpoint, both produce the same average power (AP). This is confusing and outright misleading for a lot of people. This is where normalized power (NP) comes in.
NP is basically an algorithm that computes the “load” of a particular segment of data. Instead of averaging it, it removes peaks and valleys from the data to effectively create a smoother, more realistic representation of data. This comes in handy in the real world especially if you’re riding a segment that doesn’t require you to pedal continuously at a steady effort.
Variability index (VI) is basically your NP divided by your AP. This shows how steady or punchy your effort is. If you hold a steady effort, your NP and AP are going to be very close to each other, resulting in a VI of close to 1.
If you’re surging and backing off constantly, your VI will be higher than 1 and realistically have a value close or higher than 1.1. Efforts higher than 1.1 usually mean you had a lot of peaks and valleys during a ride or effort.
In some cases this is unavoidable (e.g. hills and criteriums) but if you were time trialing or racing a triathlon, it takes a lot out of your legs. Remember, every time you surge, you’re burning matches and you have a limited number of matches available to you. Holding a steady smooth effort usually results in faster times and fresher legs come T2.
Aerobic decoupling is not a metric you can easily get from data unless you have more advanced software like WKO or Golden Cheetah. Basically, it’s how your heart rate increases for the same effort or wattage.
Let me simplify things: Think of your power as your independent variable, something you can control and manipulate. Heart rate, on the other hand, is your dependent variable, something that is an outcome of any changes you make to your independent variable (power).
In a perfect world, if you hold 150w, your heart rate will be constant no matter how long you hold 150w. However, in the real world, fatigue, dehydration, and other external variables also affect the heart rate. This means that as the workout progresses, your heart rate will increase even if you hold 150w exactly.
A good sign that you’re aerobically strong for that particular power and duration mix is if your aerobic decoupling is below 110 percent. That means your HR increased by 10 percent or less during that particular ride. If it went up more than 110 percent despite holding a steady wattage, you’d probably need to look at dialing back your power or increasing your fluid and fuel intake.
There is definitely more information you can extract out of your ride data, but these metrics can get you off on the right foot. From experience, taking a look at these data points can allow you to plan around your training. Taking them into account can help you train better, pace yourself better, and nail that perfect bike split.
Have some training questions, feedback or suggestions for future articles? Drop a note in the comments section below or on Facebook, Twitter or Instagram. You can also get in touch with Don directly here.