I think 73-77% is still relevant as a starting point. I see this chart referenced a lot also.

I agree! Been using this a lot too. I wonder if, now that bikes and positions have improved so much, if the numbers in that table are still 100% reliable. I think bike splits have become 10-15 mins faster over the last 10 years for AGs, at the same watts .. just a thought..

Watts and IF don’t care how fast you are going…

I use a mix of lactate and testing in training. During the IM prep (last 12-14 weeks) I like to start 20 watts below my LT1, and do maybe 3x40 minutes in the TT position. If that feels good and I can hit 100 grams of carbs pr hour, next longer session I bump it up 5-10 watts. With 2 sessions of TT training around IM pace a week, it gives me around 20 sessions in the build up - to hit the right intensity. I try to get 2 sessions with 4 hours of specific intensity before the race - to get a feel for going fast and hitting my nutrition.

I coach some athletes without access to lactate - but it's almost the same thing. When they go too hard in training (they almost always do at some point in the build) we know they hit above target. Also X x 30 minutes starting conservative and then adding 10 watts every interval, you can almost feel where your limit is.

To make sure - try to swim hard in the morning, bike 5 hours including 4x50 minutes @ racepace and then run your long run the day after. How did the run feel? If it takes more than 4-5k to feel "normal," then you went too hard on the bike the day before (or didn't fuel enough during or after the bike).

I agree! Been using this a lot too. I wonder if, now that bikes and positions have improved so much, if the numbers in that table are still 100% reliable. I think bike splits have become 10-15 mins faster over the last 10 years for AGs, at the same watts .. just a thought..

Just remember that HR drift could also be a sign of dehydration and not overpacing :)

That's why I like the longer run the day after, to make sure I'm good.

I know that its a theory that you can run your IM marathon at +15-20minutes compared to your open marathon time, but I don't see many people doing it in the AG ranks. The vast majority, even those getting good results, are more like 25-30.

---

Dimond Bikes Superfan

I know that its a theory that you can run your IM marathon at +15-20minutes compared to your open marathon time, but I don't see many people doing it in the AG ranks. The vast majority, even those getting good results, are more like 25-30.

The rule isn't that AG's *will* be +15, the rule of thumb is that to have their fastest time they *should* be +15. Those AGs with good results 25-30min slower could have theoretically had a faster overall time if they did the bike 10 min slower and the run 15 min faster.

(of course this is also very dependent on training history. Someone doing 8h/w is never going to be +15 on an IM marathon. A top tier pro can be expected to be inside 15min regularly)

OK, I just don't know anyone in AG ranks that actually does it. The pros seem able to do it, but not because they are pacing the bike better. If anything, they are doing more surges and riding harder overall. Perhaps total training volume or bike training volume are the big key factors.

I was curious about someone who won my AG at a recent IM in an outstanding time. Turns out they have been a world-class AGer, if that's a thing, for many years. Google shows me a calendar year 1:16 half vs their IM run time of 3:07, which was the fastest run split by a lot. 1:16 probably equates to very low 2:40s open marathon time, i.e. +25ish minutes. Could they have ridden 5min slower and run 10min faster? Maybe, I don't know, just doesn't seem anyone actually does it.

But if you're prepared for the last block of race specific training - you can "test" the bike maybe 3-4 times before the actual race. Yes, sometimes the truth is hard on the ego, but better failing in training than at the race. I guess if you never fail in training, you never know where the limit is. Then you taper - and think your can go from 70 grams pr hour and 240 watts in training to 110 gram pr hour and 260 watts in the race.

My best bike/run combo was in 2021. 10 days out from the race I did 2x50+2x30+2x20 minutes @ 8-10 watts higher than in the race on a flat course in the TT position with TT-helmet. The day after my long run was "good" - but not great like the week before. I knew I got the carbs before, during and after the ride = the power was just a bit too much. I ran exactly 20 minutes slower on the marathon in Almere (September), than a stand alone in April the same year. Almere was a bit hotter than the 10 degrees celcius marathon in April - which should be the 5 minutes longer than the "15 minutes rule"

But if you're prepared for the last block of race specific training - you can "test" the bike maybe 3-4 times before the actual race. Yes, sometimes the truth is hard on the ego, but better failing in training than at the race. I guess if you never fail in training, you never know where the limit is. Then you taper - and think your can go from 70 grams pr hour and 240 watts in training to 110 gram pr hour and 260 watts in the race.

My best bike/run combo was in 2021. 10 days out from the race I did 2x50+2x30+2x20 minutes @ 8-10 watts higher than in the race on a flat course in the TT position with TT-helmet. The day after my long run was "good" - but not great like the week before. I knew I got the carbs before, during and after the ride = the power was just a bit too much. I ran exactly 20 minutes slower on the marathon in Almere (September), than a stand alone in April the same year. Almere was a bit hotter than the 10 degrees celcius marathon in April - which should be the 5 minutes longer than the "15 minutes rule"

I fuel like in a race - around 50-60 grams pr hour. I run loops or have my girlfriend on a bike with bottles :)

I eat full breakfast before and I don’t try to limit carbs, as I think my limiter is my muscular Endurance and not my ability to ‘turn over energy’ <—- sorry I don’t know the english explanation/words

I'd further argue that your IM bike ride should be one of your easier long rides of those last 6-8 weeks of training.

Is it just the RPE difference between being tapered vs in-block training fatigue? Or is is because those long rides in IM training should be down above IM effort (like you're example of including 70.3 efforts into the long ride)?

To make sure - try to swim hard in the morning, bike 5 hours including 4x50 minutes @ racepace and then run your long run the day after. How did the run feel? If it takes more than 4-5k to feel "normal," then you went too hard on the bike the day before (or didn't fuel enough during or after the bike).

I did a "fun" experiment at IMTX this year. The context was that I was training for the Comrades Marathon (89km ultra road race in South Africa), which has about 20,000 participants. Your start corral is based on your qualifying marathon time, with the front one (the A group) requiring a sub 3 open marathon. However, you can also qualify with an Ironman run time, which for the same A group qualification, only requires a sub 3:30 run. I did my winter training block, with everything on target for a sub 3 at the Houston marathon. However in the race I had a super weird issue with quads totally seizing at mile 11. I walked the rest of the marathon, since I had to at least finish one marathon to qualify for Comrades at all. It was something like a 4:25 which basically had me in a really bad starting batch for Comrades. So I had to do another marathon if I wanted a better time. I then did the LA marathon, aiming for just a decent qualification but not the best, conservatively shooting for a 3:30. I ended up doing 3:31 or something, so bettering my starting position but still not the best. I was holding back a little bit in that race because I didn't want to blow up again but I was totally spent at the end. Maybe at best I had a 3:20 in me that day.

So then I thought, what if I do IMTX, and just sandbag the whole race up until the run and then go for it. So I swam super easy, soft pedaled the bike, spent 20 minutes getting ready in T2 and then went for it on the run. I ended up with a 3:28, which although I've run faster than that before, was about the same as my best open marathon at that point in time. Of course, I gave up a lot of time on the bike (probably 40+ minutes at a guess) so this would be a really poor strategy to get a good IM time, but it does provide the extreme end of the spectrum for what happens if you save yourself on the bike. For what it's worth, my best overall IM times have been off really hard bike rides. It just becomes a gamble as to whether or not you blow up on the run. For me, the main factor in blowing up (or not) on the run was always related to the bike hydration, heat management or nutrition, not the bike power output itself in isolation.

---

____________________________________

Are you ready to do an Ultraman? | How I calculate Ironman race fueling | Strength Training for Athletes |