It's not going to change beyond the margin of error right there at peak training weeks before a race. I typically monitor mine every couple of months with an actual test, but generally can tell based on my 2x20 workouts and 5x5 workouts as the power inches up. I don't think you need to be so specific as to get an exact number at a set date before a race, so maybe 3-4 weeks before sounds right if you can fit it into your schedule.

How exactly would you use your FTP number for your IM race? Curious...

Different ways to look at it. 3-4 weeks out will be your biggest CTL ad most fatigue so it won't be a good indicator of your tapered FTP. That's good in that it will be conservative on race day but bad in that you could be leaving money on the table. I'd rather pace the bike conservatively and have a great run though. Personally I'd do it maybe 10-14 days out. Assuming you do some version of the 20min test it's a good high quality, low volume session without a lot of residual fatigue.

I go much further out. Being able to do 20 min at x watts, doesn't mean you can do 5+ hrs at 70-75% of that and still run well. Maybe I'm too conservative, but I've done 8-10 weeks out, and then make sure I can do my long rides / simulation workouts at my planned IM watts. I'm not sure you would see a huge bump in your expected race watts if you tested 8 vs. 4 weeks to make a big difference in what you plan to ride at in the race. I'd rather go in a tad under to be sure I'm ready to run.

FTP x .7 or .75... should be pacing for an IM.... or so I'm told :)

Might be nice to know an accurate FTP to base pacing on.

Absolutely. This is only valid if you've been doing appropriate training volume and time/distance on training rides. Same as something liek the McMillan running calculator - your 5k is only indicative of your 1/2 mary or mary time if you've been training for that longer distance.

I don't think you need to do it closer than that - it's not going to increase a huge amount over the taper - and if anything it's better to base your pacing off a lower FTP than a higher FTP. It also depends on how much the test takes out of you. For me personally, I can do an FTP test after the first week of a 3 week taper, and it actually gives me a nice little boost. i.e.

5 weeks out: IM specific block
4 weeks out: IM specific block
3 weeks out: recovery week (4 days) + FTP test only if I'm recovered and adapted (i.e. if power:HR and pace:HR have improved). If I'm not recovered I rest until I am
2 weeks out: low volume, race specific intensity (and higher)
1 week out: chill, "stop the rust" from setting in


Having said all of that, with my most recent IM I didn't do an FTP test, I just based my pacing off my "old" FTP taken about 7 weeks out. I could feel that it had increased marginally but not enough to warrant a new test. So my point is, only do the FTP test if you feel that it's changed by enough to make a difference.

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

Your intensity factor is a percentage of your FTP, so it determines what pace you will be riding the bike leg (of any race distance: IM, HIM, Oly, Sprint). For an IM I aim for 68% mainly because I want to do a decent marathon. I think it's a great idea to do a test 3 weeks before the race. I always get a bump in watts which actually serves me well in a race after a proper taper.

There is no standard optimum % of FTP. One would have to learn from experience. Generally it is probably better to set power goals for Half and Iron distance races by doing race simulation rides with a short run afterwards. Two or three such sessions in training and you dial in your ideal pace pretty well.

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Kat Hunter reports on the San Dimas Stage Race from inside the GC winning team
Aeroweenie.com -Compendium of Aero Data and Knowledge
Freelance sports & outdoors writer Kathryn Hunter

What do I know... I'm just a cyclist :)... and an old slow one to boot...

I defer to the master... :)

I'm no master.
But specificity tends to be awesome =)

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Kat Hunter reports on the San Dimas Stage Race from inside the GC winning team
Aeroweenie.com -Compendium of Aero Data and Knowledge
Freelance sports & outdoors writer Kathryn Hunter

I think it depends on how you manage the last 6-8 weeks. Personally I decided to do a race about once a month the last 5 months before my first IM. I'll use those power numbers as my best indicator since there's a far better indication of specificity than a 20 minute test.

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TrainingBible Coaching
http://www.trainingbible.com

Oh. Merr. Gerd.

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Zen and the Art of Triathlon. Strava Workout Log
Interviews with Chris McCormack, Helle Frederikson, Angela Naeth, and many more.
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Why not do an all out 20 minute test a week before to get the most accurate assessment? The tss you build from such a short duration test would hardly affect your taper or recovery.

you guys that conduct FTP tests so frequently...are you doing on the road or trainer yourself? or with your cycling coach?

Either 12 mile TT on flat road or the 20 min indoor test using trainerroad

And I only test every few months

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

I agree. I actually think pacing your IM bike off a 20' test...is kind of stupid. Sort of like pacing your IM run off your most recent 5k performance.

Is there a middle ground as well? i.e., testing to "determine FTP" (phrase used loosely), which is validated in rides with short bricks as described (meaning you probably need more than 4 weeks prior to IM to test)?

Would that not give a reasonable baseline to do those training rides in and dialing it in quicker? potentially... rather than shooting in the dark and blowing up and concluding "well, that's not my FTP clearly...."

ETA - I agree with Jason that basing IM pace off a 20' test alone is stupid without field validation. Of course, I've done that (test + validation) for one IM and 2 HIMs now, and my run has sucked balls. So i clearly got it bassackwards.

For sure...but since the OP was asking about doing the test 3-4 weeks prior to the IM...well...hard to use that as a baseline for longer rides with bricks after a test that late. Hence why I asked what the OP would do with the FTP test as far as their IM race.

for the most part, i'm dialed in on my long rides. since i still have a few long rides before TX, I just wanted to know at what point you should just go with what you've got...seems like you'd need at least 2 rides to validate FTP, but I could be mistaken.

I'd roll with what you're dialed in with for your long rides. There is no reason to "validate FTP" when it comes to long course. Either you can hold a given power for X hours and still run after...or you can't. You don't need to keep doing 20' tests to convince yourself, or prove to yourself that you can.

How much more do you expect your FTP to increase when most of your training is more specific and probably geared toward long tempo efforts and long zone 2 rides? That's not a recipe to build your power. That late in the season, it's diminishing returns, and I'd expect that it's unlikely to change much unless you took time off for an injury. When your already near peak fitness, improvement come very, very slowly and long rides in fact tend to compromise your overall weekly training load since intensity is lower for a given period of time and recovery is often proportionally longer.

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TrainingBible Coaching
http://www.trainingbible.com

 You should be in a relatively high training load in the last 6 weeks leading to a ironman and testing your FTP should not be a priority and smart way to burn your matches. A simple review of your weekly powerfiles in training should be enough to see if there is changes happening.

And you should not base your ironman effort on a % of FTP entirely. Long ride simulation will be more effective tool to validate what watts you should ride at...

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Jonathan Caron / Professional Coach / ironman champions / age group world champions
Jonnyo Coaching
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Agreed!