Durability
Your power, after the work.
Fresh power wins tests. Races and long days are decided by what's left after hours of riding. Two Thresholds measures that on every ride, in the work you've done rather than the minutes.
What durability is.
Durability, sometimes called fatigue resistance, is how much of your power you keep as a ride goes on. Two riders with the same 20-minute power can be far apart after three hours: one still holds it, the other has lost a big part of it. The second rider's FTP test never shows that.
So Two Thresholds keeps two power curves for every ride: the fresh one, and the best you could still do once a set amount of work was behind you. Put them side by side and you see how much of your 20-minute power is left after 2,000 kJ, and whether that gap is closing over a block.
Why work, and not hours?
Three hours at an easy pace and three hours of racing don't tire you the same. Work done, counted in kJ, is closer to what the legs have actually been through. Time on the bike isn't.
Two ways to count the work.
- Total work, from fresh up to 5,000 kJ in steps of 100 kJ. Simple, and easy to compare between rides.
- Work above CP, from 5 to 250 kJ. Hard efforts tire you far more than the same kJ ridden easy, so this counts only the work done above your critical power.
Both use your own CP and W′ on the day of the ride, so a ride from last spring keeps the threshold you had then.
Everywhere you look
Durability on the ride, the curve and the rep.
Peaks after the work.
Slide the work level and see your best powers from 1 second to 2 hours after it, against fresh.
kJ before every effort.
Detected intervals show the work done before each one.
A chart in kJ.
Switch the ride chart's axis from time to work.
The same rep, fresh and tired.
Every rep of about the same length from every ride, and how it holds up after 2,000 kJ.
Using it in training.
Look at the gap between the fresh curve and the curve after 2,000 kJ for the durations you race at. A big gap says the engine is there and the endurance under it isn't yet.
To work on it, put the key efforts late in a long ride, after the work, and compare them with the same efforts ridden fresh. Compare intervals shows each one next to the others, and the planned W′ balance in the workout builder shows how deep a session should go before you ride it.
Coaches see the same numbers for every athlete. With the AI connection you can simply ask: "How much of my 20-minute power was left after 2,000 kJ this season, compared with last?"
Questions about durability.
What is durability in cycling?
The power you can still produce after a given amount of work in the same ride. It's measured as your best power for a duration, such as 5 or 20 minutes, after for example 2,000 kJ, compared with the same duration fresh.
Why measure it in kJ and not hours?
Because the cost of a ride depends on how hard it was, not only how long. kJ counts the work. kJ above CP goes further and counts only the hard work, which tires you most.
Do I need a power meter?
Yes. Durability is worked out from power data, from a power meter or a smart trainer. Heart rate alone can't show it.
Does it work on old rides?
Yes. Import your history from Strava, TrainingPeaks or intervals.icu and every ride with power gets its durability curve, using the threshold you had on that day.
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