Your FTP test went beautifully. You were fresh, hydrated, caffeinated, and the numbers looked sharp on Zwift. 💪
But here’s the honest question nobody wants to ask on a Tuesday morning: can you still hold anything close to those numbers after two hours in the saddle?
Because that, quietly, might matter more than your fresh FTP ever did.
What the new research actually says
A study by Inoue and colleagues examined 25 male cross-country mountain bikers and compared their fresh power profiles with those after a demanding 140-minute protocol. In other words — how many watts could they still push after already doing real work?
The gap between the stronger racers and the weaker ones was bigger than you’d expect:
- The better race performers lost around 4–8% of their power across most durations.
- The lower performers dropped by roughly 14–20%.
Same fresh FTP on paper, wildly different rides in reality. 🚴♀️
Why “durability” matters more than a fresh number
Most of us treat FTP like the whole story. It’s the number we obsess over, the one we screenshot, the one we quietly compare to that person in the group chat. But FTP tells you what you can do when you’re clean, rested, and warmed up nicely — not what you can do at kilometer 80 with tired legs and a headwind.
Durability is the missing piece. It’s why someone can drop you in the last 20 minutes of a group ride, even though your FTPs look identical on Strava.
Fresh FTP tells you what you can do. Durability tells you what you can still do when it counts.
A cautious, repeatable durability check you can do on Zwift
Before we go there — a big honest asterisk. The study was small (25 riders), male-only, and specific to cross-country mountain bikers. The findings are interesting and useful, but not gospel. So we’re going to be sensible.
Here’s a simple, repeatable indoor benchmark you can do on your trainer every 6 to 8 weeks — not every ride:
The durability check: 110–170 minutes before any cool-down
- Warm up for 15 minutes at an easy Zone 2.
- Ride 90 to 150 minutes at solid endurance pace (around 65–75% of your FTP). This is the “work” that fatigues you.
- Then, without a long rest, do a 5-minute all-out effort at the end.
- Record your average power for those 5 minutes.
- Compare it to a fresh 5-minute effort you’ve done recently (or one you do on a separate day the following week).
The percentage drop between your fresh 5-minute power and your fatigued 5-minute power is your rough durability number. Track it over time. It’s a much more honest indicator of race-day fitness than another fresh FTP screenshot. 📊
Please don’t turn every ride into a suffer-fest
This is important. Durability testing is a monitoring tool, not a training plan. If you slap a hard 5-minute effort on the end of every long Zwift ride, you’ll be cooked in three weeks. 😅
Use it sparingly. Once every 6 to 8 weeks is plenty. In between, keep doing your endurance rides as endurance rides — because that’s actually what builds durability in the first place. Long, steady, mostly boring time in the saddle is the answer. Not more suffering.
🚴♀️ New to Zwift or indoor training?
Grab the Indoor Cycling Starter Pack for R129 — everything you need to actually enjoy training indoors, from setup basics to load-shedding survival tips, honest gear notes, and a printable checklist. Written for real South African riders, not pro racers.
The takeaway
A fresh FTP is a nice number. But how much of that number you can still produce two hours in — that’s the number that actually decides how your race, your group ride, or your Sunday long spin plays out.
Test it occasionally. Track it honestly. Then get back to doing the boring endurance work that actually moves the needle. 🩷
🩷The Endurance Diaries🩷
