Dan, I think I can humbly say I may be able to speak to this issue with some authority. I was, WAAAAAAAY back, the first ever (pro or age group) to break 3 hours at IM Canada. I went 2:55. Trust me, 15 years later I’m not exactly doing that. In fact, I’m desperately struggling to hold on to my Marathon split while raising my swim/bike times. Not an easy task. I think Fleck hit on it pretty well with the theme of raising cycling fitness to the level where you can get off the bike in a relatively unfatigued state and then use strength to get a solid pace rolling in the Mar. Let’s be honest, few people are going to really be drawing off “speed” as such in an IM Mar. It’s purely an aerobic threshold effort. You’ve got to get efficiency or aerobic threshold levels up to a point where you can run say 8 min. miles without fatiguing heavily. How to do this?
IMO there are these factors:
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innate talent for running
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strength as defined as ability to run at an aerobic threshold pace for a long time w/o fatiguing
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nutrition
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mental focus
Numbers 2-4 are within your ability to control. Strength can best be gained by having trained at or near your Lactate Threshold on regular occasions in the final weeks of the buildup. This is best done with Tempo runs at but not exceeding LT for approx. 20-30 minutes. Add a few long runs to build metabolic efficiency and endurance at AT and you should see improvement.
I really do not think a lot of emphasis on pure 10k type speed is that productive at the injury risk it poses. If that were the case, then by extension we would be doing much more concentrated speed work on the bike too like track pursuits etc. which I do not hear being advocated. Instead, you have people like Larsen recommending a lot of ten mile time trials and such. What is that, basically a Tempo workout.
If you really want to try and reach some corellation between 10k times and Marathon or Olympic distance and IM, then use 4.66X your 10k or Oly. Tri to get a predicted Mar. or IM time, it’s pretty darn close. Having said this, it’s my O that your Mar. split in an IM is somewhere around 25 to 35 minutes slower than you would run in an open Mar. Now, this is troublesome because a lot can get your IM split drifitng (usually slower, heat, nutrition etc.) but, you can play around with this for fun. Say, you ran 40 min. for 10K, you multiply by 4.66 and get 3:06:24 for a Marathon. OK, lets add in 25 to 35 minutes and you get a 3:31 to 3:41 IM split. 4.66 is academically derived from several of the exercise phys. guys, the 25 to 35 minute rule is my own seat of the pants theory. FWIW. Play around with 4.66 times Oly. tri times and you see some interesting prdictions. Ie., 2:20 X 4.66 = 10:52.
The question I would like to pose, is, should we be going with our own personal strengths or continually working on weaknesses? I find to a degree working on weaknesses is a risk in that it starts to cannibalize your personal strong points. Any thoughts out there?