There are two terms that you will see and hear about for any training plan and on Zwift. The first is called 'Watts per Kilogram' (w/kg). The other term is called 'Functional Power Threshold' (FTP). Understanding both of these will help you improve your abilities as well as work towards a successful training program
Watts per Kilogram (W/kg)[]
The 'Watts per Kilogram' metric is simply the power to weight ratio or the amount of watts (power) you output per kilogram (2.2lbs) of weight. To calculate your W/kg, you take your watt output and divide it by your weight in kilograms. For example, a 70kg rider who outputs 160 watts would have a 2.29 w/kg number. W/kg is not a static number, but rather one that corresponds to different durations on the power duration curve. For the purposes of power profiling, there are four standard durations: 5 second, 1 minute, 5 minute, and 20 min (FTP). These are the durations that best reflect neuromuscular power, anaerobic capacity, maximal oxygen uptake (VO2 Max), and lactate threshold (LT), respectively.
Watts per kg provides athletes and coaches a metric to compare riders of different body composition to one another, as well as understand how effective an athlete’s training is for the demands of a specific ride or race. There are several ways to improve your W/kg once you understand how to train it and why you should train it. Shifting some of your focus towards this metric will no doubt produce big gains on the bike.
Zwift W/kg Categories
As you ride/run in Zwift, your W/kg will be displayed next to your name. It will change as your power output changes. This is also why having an accurate weight entry in your profile is important. It should be updated as your weight changes significantly. Additionally, many group rides/events are stated to ride at a given W/kg ratio or are broken into W/kg categories. Zwift color codes these categories for ease of picking the best ride for your abilities. This is important so that you know how fast the pace is going to be for that ride and how much effort you will need to put out to stay with the group. For example, after riding in Zwift awhile, you know your average W/kg is about 1.8. Yet, there is a group ride that advertises a pace of 2.5-3.0 W/kg. You can either expect to have to put out a lot more effort to stay with the group or expect that you can't keep up and will be dropped. There's nothing wrong about riding with a faster group than you but don't expect them to slow down for you when they advertised a faster pace.
Here are some additional articles to learn more about W/kg and methods to improve it:
Power-to-weight ratio explained: why W/kg is important and how to improve yours - Bike Radar
Why Cyclists Should Focus on Watts per Kilogram - Training Peaks
Power-to-Weight Ratio for Cyclists: When Watts/kg Matters, and How to Improve It - Trainer Road
Functional Power Threshold (FTP)[]
Functional Power Threshold (FTP) estimates the highest average power you can sustain for one hour, measured in watts. In cycling, FTP is a measure of fitness and indicates the amount of work you can sustain for long durations. Think of FTP as a benchmark for you to try and beat, the same way you try to beat your max rep at the gym. It’s a number that indicates your current level of fitness, and sets the bar for improvement. It also shapes your training zones in workouts, personalizing your experience.
FTP is a measure of your cycling fitness and ability to maintain a high but manageable power output for a somewhat lengthy duration. From a physiological perspective, it’s the cycling power you produce when your lactate production has risen, leveled off, and then closely matches your body’s ability to remove lactate. This just barely keeps that lactate flooding at bay. In cycling, FTP is that grey area between the power you can sustain for a very long duration, typically an hour, and the fleeting power you can only tolerate for a couple of minutes.
If you know your FTP number, you can enter it when you create a Zwift account. When it needs updating, you can do so in game from the ride menu. Once you’re on the menu screen, select the edit box under your name. You can change your FTP using the box on the right beside your max heart rate.
If you don’t know your FTP, you can take one of Zwift's FTP tests. Choose them from the workouts page in Zwift. There are three FTP tests to choose from: 1 hour, 45 min or 20min. Make sure you’re well rested, and have plenty of water on hand. These tests determine your highest threshold - so there will be sections where you’ll give it your all. For more tips on how to tackle an FTP test, click here.
If you have a smart trainer, the warm-up will utilize ERG mode. Once the actual tests begin Zwift automatically turns off ERG mode. ERG mode needs to be off during these tests so you can generate as much power as possible. If ERG mode is left on, your trainer will hold you at a target watt range regardless of how fast or slow you pedal - resulting in inaccurate test results. Here's a brief description of the FTP tests that you can take on Zwift.
FTP Test in Workouts
FTP Test[]
The standard FTP test starts with a long easy warmup, a few ramps, and a 5-minute effort to get the legs pumping. After that, it's time to give it your all - and go as hard as you can for 20 solid minutes. Pace yourself and try to go as hard as you can sustain for the entire 20 minutes - you will be scored on the final 20-minute segment. Upon saving your ride, you will be notified if your FTP improved.
FTP Test (Shorter)[]
The short variation of the standard FTP test starts off with a short warmup, a quick leg opening ramp, and a 5 minute hard effort to get the legs pumping. After a brief rest, it's time to give it your all and go as hard as you can for 20 solid minutes. Pace yourself and try to go as hard as you can sustain for the entire 20 minutes - you'll be scored on the final 20 minute segment. Upon saving your ride, you'll be notified if your FTP improved.
FTP Ramp Test in Workouts
FTP Ramp Test[]
This is a ramp test designed to estimate your FTP. A ramp test uses a relatively short progressive build of one-minute steps to identify the upper limit of your aerobic capacity quickly. The ramp portion of the test should, ideally, take about 5-20 minutes to complete. It should start out feeling extremely easy. And then, rather suddenly, it will get much, much harder. It is at that point - when the difficulty really shifts - that you need to dig in.
From there, you should max out within 3-5 minutes. This is a maximal effort until exhaustion. You are trying to record your absolute best one-minute power. So keep pedaling until you simply cannot go any further. At that point, stop pedaling, and the test will automatically end and shift to a nice long cooldown. This is a seated test with a focus on smoothness and consistency. Focus on keeping a good position on the bike with a nice steady cadence of ideally 80-95rpm. Expect your cadence to fall a bit near the end of the test; that is normal. Just don't let yourself get bogged down and mashing. The focus here is on aerobic power.
FTP Ramp Test Lite[]
This modified version of our original ramp test (above) is for lighter (under 60kg/132lbs) and more novice riders (<2 w/kg FTP). This test starts at a much lower wattage, and increases in smaller steps each minute, compared to the original ramp test. This results in more accurate FTP test results for our lighter and more novice Zwifters.