VI vs. IF for pacing Ultra event

I have a question regarding Variability Index compared to Intensity Factor.

I’ve got a 340 mile/34 hour race in April. Course profile will be a death by a thousand cuts, 100 ft of elevation gain at a time with a race total expected around 25-30k ft. Due to that there will be lots of coasting and also a decent amount of time in the temp-ss range. Doing this in training has shown a VI larger than I’d like, Usually around 1.07, due to the nature of the course with lots of zero’s on the power from coasting downhill. Would IF be a better option to keeping the effort in check?

That is a huge effort! Will you be riding for survival or with a specific goal in mind? For the bike leg in an Ironman usually pace for target power, personally I like having my lap NP displayed and then stick to a certain plan based on what IF I want to stick to. For an Ironman a typical range is somewhere between .65 and .7 I’d say. Coasting is fine, it I’d be very. careful how hard I push into the inclines, over that distance I wouldn’t want to see anything in SS on my display. Keeping it down low, no matter how slow it might feel is probably a smart move.

For actual pacing neither VI nor IF seem particularly suited. I’d use those to build my race plan and then have either lap power or lap NP and maybe 3sec power displayed to modulate my effort during the ride.

1 Like

I would not pace by watt, but by feel.
You could use watt for a cautious ceiling during the first hours. But if you try to hold a certain if (let’s say 0.65) after 16h and your body could only deliver 0.6 during that hour, you dig your own grave.
During IM pacing with power and feel worked good for me, but for my 500k with 5500m elevation I just tried to go very easy during the first hours, and after that, your body will tell you very clearly what he is capable of at that moment (and this will vary often times).

i wouldn;t be too concerned with VI, only because depending on the descents you could actually do yourself some big favors by coasting and soft pedaling them. Keeping an IF cap on the climbs will be critical, and that means ensuring you have the adequete gearing to be able to spin up the climbs at the required wattage to avoid going too deep.
This is almost one of those distances where I would be planning to go “too easy” the first half just to ensure that i didnt get things wrong for the back half. For example, maybe starting at a 0.6 IF or slightly below for the first half, so that you can push that up to a 0.65 for the latter half and actually hold it may not be a bad strategy.

For longer events, my thinking is that the most “costly” efforts are those close to and above threshold. A combination of IF and VI can give you some sense of how much time you’ve spent there, but perhaps just tracking this directly might be better? Garmin head units – and I assume others – have a field for “time in zone” that you might use. If you can hit your target IF without increasing your “time in zone” at/above, say, 90% of FTP, then that might help keep things where you want.

You are going to want to set a max ceiling to watts and IF (IF will be higher in the first few hours as groups get sorted out) and have a target for average IF. A race of this duration is a eating race first. When you are going over target average IF find a place where you can bring it back down and work hard to take on more nutrition to make up for the cost of going to hard. Don’t be afraid to talk to your riding group about how you are doing with pacing/feeling/nutrition. Also don’t coast to much, but go to low z1 instead. Coasting and restarting on rides of this length is another form of death by a thousand cuts.

This is where my mind went today while thinking about it. Setting a max power limit. I tried that this weekend on my long training ride(8hrs) It is for sure a challenge to try and keep the effort that low. Hoping no dogs on course, I don’t want to have to throw down a sprint to get away from a dog!

Good thought on lower power spinning vs coasting.

You might not have a choice: have you experimented with your setup? I have an “extreme triathlon” this year and downloaded the GPX ride file from the website. I’ve the ridden some of it for training indoors with the trainer simulating the gradient. I got a temporary subscription to RGT cycling as it simulates the braking. A wide enough range of gears is impossible. If I want to have a reasonable cadence going up hill I end up coasting down steep downhills. Also there are corners you have to brake: no point braking and pushing on the pedals simultaneously.

Both VI and IF are affected by periods of coasting. I personally just keep an eye on 10s power and ensure it doesn’t go too high. I also avoid grinding as I think that screws with the run: I once got stuck in the big ring and it made the running real hard (I think).

Edited to swap fullstop for question mark