Pacing a 24 hour MTB Marathon with a PM


Can anyone give me advice on how to pace a 24 hour MTB marathon using a power meter and garmin, based on the following stats?

FTP 275 watts
Aerobic threshold power 220 watts (HR 140 bpm)
At Aerobic threshold, my Respiratory Exchange Ratio (RER) is 0.8
Weight 77kg
Vo2 max 61.8, for what it’s worth.

Course: 12km laps repeated for 24 hours. The course is on the side of a hill, therefore long steady climb to the top followed by undulating tech single track and fire road working back to the bottom.

Starting point for this - assume I know nothing!
I’m not even sure if I should be using the average power of normalised power field on my Garmin?!

Any help in deciding a pacing strategy very much appreciated!


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Ride to feel more than anything and a lot of the race comes down to being a mental game, along with eating / drinking plenty.

Thanks for flagging this article - really useful!
If I work to the suggested IF, with an RER of 0.8 I’m still going to struggle with fuelling myself to keep going beyond 18ish hours, as insufficient energy is being derived from fat metabolism. The event is 10 weeks away, so i’m Going to incorporate some long fasted rides into my schedule to try and raise the % of energy derived from fat metabolism.
Have you ever tried these? If so what was the optimum intensity?

I’ve never done a 24h race. 12h is the maximum for lap style race formats for me. HOwever, with these I do have quite some experience.

I must say I’m not a firm believer in FTP & IF. Especially not for endurance racing. Nice concept when getting into using a powermeter but there are too many caveats with it. For example “repeatibility” is not included.

I do not set targets for laps. I set an upper limit for the slopes. For a 24h race I would probably go with AeT as a threshold. And then go with the “flow”. At some point it will be entirely mental anyway. After quite a few years of racing with a powermeter I know what wattage I can hit under certain conditions. Only for shorter races (<4hours) it’s simply going all out from the beginning and surviving to the finish.

Furthermore, I’m not really a believer in met testing either. And especially not for endurance racing with intermittent efforts. One does the test usually with fully loaded endogenous fat (intramuscular triacylglycerides -IMTG) and carb (glycogen stores). After about ~120min fat metabolism switches to other sources. Hence, a met RER is only valid for the first 2 hours [ ]. And then there are so many other confounding factors with met testing [ ] , personally, I’ve seen too much nonsense data out there.

But this is just my very personal opinion …

Interesting, and thanks for the reply.
Plenty to think about! The only certainty having never done one before, is that i’ll get a PB!