Extrapolate FTP for endurance?

I am training for a century (160km) and then want to work towards a double century (320km). I was wondering, how do I calculate how much wattage I can/should average over longer distance riding?

Do you try to say within a certain FTP zone over longer period of time? In endurance-tempo? Or slower than that?

So far, I have averaged 167-170 watt over 3-4 hours (100-120km) with an FTP of around 190 last summer.

I think the best way to think about it is as IF, or what percentage of FTP is sustainable for the length of your event. For something like a century, probably nothing above 75% (IF .75) average.

I did tour of Flanders this year (174km) at an IF of .72 and felt great the whole day.

1 Like

Good idea… but how do you go from duration + watt to IF? Is there a formula I can use?

IF is simply Normalised Power over FTP. So NP of 170W on an FTP of 190W gives IF of 0.89. IF calculation doesn’t take into account duration, but the IF you are capable of holding decreases as the ride gets longer. I.e. For a ride of 1 hour you should be able to hold IF of about 1.0, for a 5 hour ride then maybe something like 0.75-0.8.

NP is a weighted average which gives more weight the higher above threshold you go. So if you ride very steady power then NP should be extremely close to Average Power. If on the other hand it’s a very spiky ride with lots of hard bursts to deal with climbs and accelerations, interspersed with lots of easy riding or coasting, then NP will be a lot higher than AP.

Edit to add: generally for distance riding you want to stay steady and keep NP and AP pretty close to each other. The exception would be if there are a decent number of cyclists on the course then it’s a lot more efficient staying in a group and benefiting from the draft. So may be worth going above your sustainable watts for short periods if this enables you to stay with a group that gives you lots of easy speed at low watts on the flat.


IMO duration (TTE?) is primarily a function of your fueling strategy.

Well not completely right. I cannot ride 3 hours at 105% of my FTP. There is some proportion of FTP (watt) vs duration. Of course, fueling strategy is super important. Also working on that.

That is of course true in a sense. My point is that there are several ways for the body to meet your power demand. If you are at 105% you will burn through your carbs in minutes; it is still possible to extend that time frame some by drinking carbs during your effort.
Contribution of energy supply

During long rides you are relying primarily on aerobic work burning fat with some help from carbs. If you stay in Z2 probably ride >300km without problem, but if in a hurry you have to provide carbs to support your aerobic system with your glycolytic system. The IF you can hold above roughly 0.65 - 0.7 up to FTP is largely depending on how much carbs you can process.
The Application Of Specificity: Triathlon And Cycling


I’ve found this document helps me decide what FTP to stay under\average:


I think FTP plays a less significant role for these rides than your VT1 (2 mmol barrier) You should really train for endurance (doing hours on the bike) instead of focussing on FTP development.


Thanks! That’s very informative.

1 Like

The correlation between FTP and, say, 5 hour power is >0.95.

I think 0.65-0.70 IF is probably something to aim for conservatively, I know of some people who have done 100 mile gravel races around 0.8 IF, which just sounds insane to me. During a 150mile gravel event I had an IF of around 0.7 around the 100mile mark, ended up riding with someone and at an easier pace and ended up with 0.65 at 150 miles. I did 2 other solo centuries this summer and both of those were 0.67, and were steady I wasn’t out to set any records. For me, 0.7 and higher would be something I’d do in a hard group ride/race and takes a certain degree of mental effort on my part to maintain on a solo basis. Personally, would love to get to a point where I can ride over 0.7 IF for century rides

1 Like

Awesome! That is one of the best sheets I’ve come across. Thanks!

Currently, I’m doing SSBMV1, then I plan to do SSBMV2 and Sustained Power Build MV. After that, it’s probably around April, and I’ll start training for endurance again. Over winter, I’m trying to up my FTP.

I feel that doing endurance rides is more “stretching out your FTP”, but not so much “improving your FTP”. But perhaps I should train differently.

1 Like

That is my approach aswell.

There was a piece of research reported on here in the UK about endurance activities. The basic question was “What’s the most effort that someone can do indefinitely?” And by “indefinitely” they really did mean “forever” as marathons were seen as sprints and participants in races like the full length Iditarod were at the short end of the scale.

The limiting factor turned out not to be fitness but nutrition as there’s a maximum that the gut can absorb per day so from that it’s pretty easy to work out the power you can output. From memory it was under 1W/kg for an average sized person.

So the “stretching your FTP” idea is closer to what’s required, you be better aiming to reduce weight as you’d still be able to digest the same amount of energy but you’d be more efficient at using it simply because you are moving less mass.

Suitably trained and with a good base I think most cyclists should be able to maintain a level around 65-70% of FTP for a day providing they fuel and hydrate correctly.

The only way to know for sure is by trial and error - especially for long 6+hr rides where you risk “running out” of glycogen.

Things can be going fine for 5-6 hrs and then the wheels can come off if you haven’t been fueling enough, or if you’ve been riding at too high a pace

Are you racing? Or just riding?

Nate and Jonathan have mentioned using Best Bike Split before.


As i see, he wants to do 320k, which means more than 10 hours