We’ve already talked a bit about how to train with Zwift but for folks not accustomed to power training the concept of FTP and training zones is uncharted territory. What does it mean? Do you need to do an FTP test? And how does it affect your Zwift riding?

Understanding FTP

FTP, or functional threshold power, is theoretically the point at which your body begins to substantially rely less on fat for fuel and more and more on glycogen. Think of your aerobic system like a funnel and the effort you’re putting  out is the water that you’re pouring into your funnel. At levels below your FTP the water drains out easily. But as you increase the pour rate, or effort, eventually the water can’t flow through the narrow spout fast enough and the funnel begins to fill up. The point at which the funnel can no longer adequately keep up with the flow of water and starts to fill is your FTP. The purpose of training is to increase the size of the spout for a better flow rate.

FTP is often considered to be your maximal 60 minute power, the best power output you can sustain for 60 minutes. This is not technically accurate but for the sake of simplicity, that’s what we’ll call it for now (you can read more about it here). An FTP test is a 20 minute effort designed to estimate your FTP. Once you have established your FTP you can determine your training zones, where each zone is a specific percentage range of your FTP. Different training systems use slightly different zones but those found on Zwift are based on Coggan’s training zones.

If you intend to use Zwift to do zone specific training, you’ll need to test your FTP. Once you’ve done that, you’ll need to have a good understanding of what riding at each zone will do for your fitness. Riding 10min at zone 2 isn’t going to do much, and you won’t be able to ride 20 minutes at zone 5. And what about zone 3 and 4?

As brief examples, zone 2 and 3 will develop your aerobic endurance (the ability to go long at moderate intensities). Zone 3 and 4 (yes, there is lots of overlap) will increase your aerobic capacity and muscular endurance (your ability to go longer at harder intensities). It goes beyond the scope of this article to explain how each zone is used to achieve better fitness (there are lots of good books about it) but to see improvements you’re going to want to target each zone for specific durations. Below is a general outline of how long your intervals should be at a given zone:

Zone 1 – Recovery. 40-60 minute recovery rides or rest between intervals.

Zone 2 – Anywhere from 90minutes to 6 hours depending on your current endurance ability. Build up by 15-20 minutes per week.

Zone 3 – 30-90 minute intervals

Zone 4 – 8-30 minute intervals

Zone 5 – 3-8 minute intervals

Zone 6 – 30s to 3 minute intervals

Going hard

The bulk of your riding will likely be in zone 3. This tends to be the self-selected power output of most riders. You’re sweating, your breathing heavier but your legs aren’t screaming at you to stop. This also tends to be the effort range that people who go hard all the time ride at. It’s a great zone and it’ll help you get faster but you’ll stagnate pretty quickly if all you ever do is go hard. If you’re one of those riders who knows they can do 2.5w/kg for their usual 60 minute ride (your going hard effort), the next time you ride, try do doing 20 minutes at 2.8-3.0 w/kg, then take a 10minute rest riding 2.0w/kg then do another 20 minute bout at 2.8-3.0w/kg. You’ll see more improvement with this method than you will riding hard for the entire duration. That’s essentially what zone-specific training is and it’s far more effective than just riding your maximal effort for your entire ride duration.

Do you need to know your FTP? 

If you ride Zwift for the pleasure of it and you are just looking to maintain some fitness during the winter, then no probably not. The vast majority of riders don’t need to get into power-based training. We hear about riders all the time who have started riding more than ever before during the winter because of Zwift, and just that increase in volume throughout the winter will be enough to see gains when you get out on the road. On the flip side, there is nothing wrong with doing an FTP test and using it to heighten your fitness through targeted training.

Knowing your FTP won’t help tell you anything about your riding ability. If you tested your FTP and found out it was 300w, that would be impressive if you were 55kg but not if you’re 85kg. From a tech standpoint almost no power meters are equitable in their measurements so unless you’re comparing yourself to someone using the exact same power meter as you with the same calibration and testing protocols, it’s difficult to gauge your ability next to others. Check out our article on how easy it is to inflate your FTP by manipulating your training and testing protocols.

There are general outlines, of course. An FTP of 4.5w/kg or higher is considered very good. But what would it really tell you? Are you a better rider than someone with an FTP of 4.0w/kg? Maybe. But maybe you have poor aerobic endurance and you crack after riding 2 hours whereas the guy with the lower FTP can go for 6 hours. Maybe you have terrible fatigue resistance and can’t handle surges and accelerations over rolling terrain. Or maybe the guy with the lower FTP drafts behind you and then out-sprints you at the town sign because his 5 second power is way beyond yours. Maybe the ‘weaker’ rider has excellent muscular force and can ride up steep grades at low RPMs better than you can? There are so many different strengths and weaknesses and variables in riding ability that FTP alone is not a predictor of relative ability. If it were the person with the highest FTP would win every bike race. But they don’t.

The fundamental purpose of FTP is to determine how to best train. It’s used to determine effort levels that correspond with different physiological processes and to elicit certain types of adaptations based on those efforts. It became a measure of relative ability because determining that number involves completing a test. And whenever a test is involved there is the perception that someone can do better on the test. And thus riders started comparing FTPs and using it as a gauge of their fitness relative to others. Training using specific power zones can help you become better at other riders in specific situations. Do you want to climb better than other people? TT better? Sprint better? Zone-based training can help you do that by determining the focus of your efforts. But don’t worry about your FTP relative to others.

But what about racing? Can your FTP be used to determine your ZTR race category?

Yes and No. On the road your category is determined by how well you do in races not by your FTP or w/kg. That being said there is a good chance you won’t finish a cat 1 race with a 3.5w/kg FTP (unless it’s pancake flat and you are beastly sprinter, but even then..). The w/kg index that corresponds to race category in Zwift is just a general outline. What it means is that the majority of riders with these FTPs finish or compete at this category. So you might find that your FTP is 4.0/wkg but you get dropped in every B-race. Your FTP tells you nothing about how well you can respond to accelerations, climbs, chasing, attacking, etc. If the pace increases to 5.5w/kg up every climb (even if its just 10-20s) and you aren’t used to that and can’t recover in time for the next surge, you’ll find yourself OTB (off the back) pretty quick even with a 4.0w/kg FTP.

If you’ve never raced before, then go to a category below what you’re w/kg suggests. See how that plays out and then bump up if need be. Also keep in mind that racing is subject to variability. If 5-10 guys show up to a race who are feeling good, are strong riders and want to work, you can guarantee that race will be far more difficult than if everyone in the pack is feeling lazy and doesn’t want to be the one to attack or work. An A race with guys who aren’t willing to work or put in big efforts could be easier than the B race where half the field wants to suffer like dogs. So don’t be surprised if you do a race and think you feel comfortable in that category, but then get smashed the next week in that same category. It happens out on the road all the time. Just remember that Zwift racing is fun and it’s meant to be a good workout. It doesn’t determine how good of a bike racer you actually are. If you place high in a Zwift race, good job. That probably feels good. But don’t let yourself become obsessed with your Zwift results and/or your FTP. Just enjoy the ride.

If you have questions about this article or want to know more please email info@humanpowerperformance.com