Wattage Explainer for folks training with power on a trainer, on Zwift, with a power meter, etc. I refer to Zwift often in this post but the concepts apply to other online training platforms as well as power on the road.
Here’s an explainer on wattage and how to apply it to your training. More important – what to NOT worry about. This is as concise as possible but will still a pretty long read. Here’s my caveat – This isn’t intended to be a comprehensive article on power training but rather a simple explanation of power and what the numbers mean. I’m not an exercise physiologist. I’m just a guy who likes to dig into things some that I have a better understanding of them. I hope that my curiosity helps you a bit.
Some of the metrics you’ll have at your disposal when riding with power as we do on Zwift are FTP, Wattage, Watts per kilogram (w/kg), heart rate, cadence.
FTP – Functional Threshold Power is the average power you can produce for 45 to 60 minutes. In most cases your FTP number will be about 95% of your 20 minute average power when doing an FTP test. Go much over your FTP number and your legs will be filled up with lactic acid and you won’t be able to sustain the effort. There are FTP tests in Zwift under Workouts (https://whatsonzwift.com/workouts/ftp-tests
Once you know your FTP number (and Zwift knows it) you can train with more understanding of your power and what to do with the numbers. If you don’t do the FTP test Zwift will determine your FTP over time.
Wattage – Seems simple, right? So why does one person produce more wattage than another person? Look at wattage this way – if 4 of us, all with different bodies and weights, rode down the road shoulder to shoulder we’d all be producing a different wattage even though we’re going the exact same speed. Same effort, same speed, different numbers. It’s simple really – I’m 6’3” and over 100kgs (let’s pretend that I’m exactly 100kgs because that will make some math easier later). Tara is shorter and weighs less, someone else is in between. For us to roll down the road together clearly requires a different amount of power. This is where power trips people up a bit – DO NOT compare your wattage to anyone else. My wattage is irrelevant to you (unless you’re a big sasquatch like me). When Tara and I are on Zwift and riding together if Tara is producing 150w I’m around 200w. But we’re likely matched in our strength to weight ratio which gets us to…
Watts Per Kilogram (w/kg) – THIS is where you can compare yourselves to others (if you want…even though you shouldn’t) and what you want to improve over time. Again this is your STRENGTH (watts) to WEIGHT (kg) ratio. You want this to increase over time. You do that by increasing your strength and/or reducing your weight. Zwift shows you your w/kg while you’re in the ride. (See image above) In the bigger pic you can see that Tara and I are riding together our w/kg is the same while we’re riding next to each other. (I had to coast to take the screenshot so I’m a bit lower than Tara is the pic.) My FTP w/kg is somewhere around 2.5. I want that to increase over time. 2 ways to do that (but doing both is the best bet) – lose some kgs or increase my ability to produce power. Here’s some simple math:
My weight is 100kgs (it’s actually higher but 100 is a nice number for the math).
My FTP is 253 (let’s say 250 for the math)
That means 250/100 = 2.5 w/kg.
So what happens if I change the weight number? My goal weight for race season is 205lbs which is about 93kg. 250/93 = 2.69. Without getting stronger or increasing my FTP my strength to weight ratio went up.
What if I increase my FTP by 10%? My FTP is now 275w. I’m still 100kgs. 275/100 = 2.75. Why even bother losing weight? I can keep the craft brewing industry booming and increasing my strength to weight ratio!
But…what I really want to do is INCREASE my strength AND LOWER my weight. Here’s that math: FTP is 275, weight is 93kg. 275/93 = 2.96w/kg.
That’s a big increase. What that means is I can increase my bike speed significantly for the same effort. (You can find that math online but you’d have to know aerodynamic drag numbers…)
So, increasing your w/kg is the goal here. Spend time on the bike and clean up your diet. Both of those things will help your cycling. You know that already but with Zwift or power measurement on your bike you have actual numbers that can show that. So get your butt on the bike and put down the beer and potato chips (*this may not be your particular dietary problem but I know a guy who identifies with this).