Triathletes like to throw fancy terms around a lot. Watts, Normalized Power, TSS, Bonk, Threshold, HRV, FTP, Aero, Friction, to name a few. I think we all have a general idea of what these terms mean, but… what do they REALLY mean?
Today I thought I’d tackle the magical unit of measure known as a watt and a few of the important terms that surround it.
So, what is a watt?
I’ve got a power meter on my bike and my Garmin tells me I am putting out 200 watts. I know if I pedal harder the number goes up. So a watt must be how hard I’m pedaling right?
Right… but it’s a little more complicated than that. First of all, you need to know what a power meter ACTUALLY is measuring. It’s measuring two things: 1) how hard you are pressing on the pedals and 2) how fast you are turning those pedals around in a circle. The terms for those two things are Torque and Cadence. Obviously there are standalone cadence sensors you can buy, which are good if you are using something like a hub based power meter (more on that later), but most crank, arm, or pedal based power meters will measure that directly.
So, a Watt is a combination of those two forces on the pedals. That means that to increase your watts you can either press harder on the pedals (usually after shifting to a harder gear) or you can spin those pedals faster. We all know that those two things will also make you go faster.
What is nice about measuring watts is that it is totally unaffected by outside sources like gravity and winds. Before you measured power, you would be focused on speed. But when you rode into a head wind, you speed would drop even if you kept the same effort level. Same thing for hills. With a power meter, you can know exactly how much you are working no matter what the conditions or terrain.
Average vs. Normalized Power
This all brings us to the two terms that are often confused by new power meter users. First is average power. We all know what an average is. We learned that in elementary school. We also use it in a lot of ways every day. Average Miles per Gallon, Average Speed, Average Heart Rate, Average Words Per Minute, etc. Since they have used an average for a long time in things like speed or pace as well as heart rate, new power meter users tend to focus on this data point. But that’s not really the most important.
Normalized power is like average power, but it is calculated to give a better way to compare rides to each other. It takes into account the time you spent coasting (0 watts), quick increases in power, and intervals. In the end, you get a number that is essentially telling you how many watts you would have put out if you had ridden at the same power for the whole ride.
Another neat variable using average and normalized power is variability index. You divide the normalized power by the average power and you get the VI. This is important for triathletes because the bike leg of a triathlon should be around 1.05 to 1.1. This means you didn’t have a lot of quick increases in power and you kept a steady pace the whole time.
Watts per Kilogram
There are a lot of other things we can get into, but I thought I’d end it with this one: Watts per Kilogram or W/kg. This is the best way to compare riders to each other. I can tell you my FTP is 211w, but that really doesn’t mean much to you. When I add in the fact that I’m 152lbs (68.9kgs) you now know that I am 3.06 W/kg. With that context you can compare riders to each other. A 100lb Female with an FTP of 139, a 200lb Male with an FTP of 278, and myself would all be on a level playing field as far as W/kg go. Obviously this really comes into play going up hills, but it does still play a role on a flat course.
I’ll have to wait until later to go into other points like Kilojoules and Kilocalories and the like, but hopefully this gives you enough information to clear up some of the confusion surrounding watts and the use of power meters.
I’d love to hear your thoughts on this. Let’s keep the conversation going! Drop me a line in the comments or hit me up on Twitter!