Help with Variability index (VI)

I have noted in a few threads people taking about VI (which I take to be the relation between normalised power and average power)

At a hilly Ironman this yea my VI was miles away from the levels that I should to be at — 1.44 across a 334 TSS / 0.67IF.

My question is how do I try and correct this?

the key there was “hilly.”

almost impossible to hold FTP in a hilly 40k, for example, or to hold a target percentage of FTP during a hilly Ironman leg.

Better for you and your coach to work out a NP target for the bike leg if it’s hilly. Otherwise, you go too deep on the uphill sections and it starts to turn into this over-under rubbish, which is the last thing you want in a tri.

Generally speaking - improved gear range and pacing

If you have an easier gear you can avoid being forced to put down too much power on the uphills and if you have a harder gear you can put down more power on the downhills without getting spun out

If the hills aren’t steep then you likely just need to reign in your effort on the uphills

The first few miles of each hill were steep. (See pic)
I think I may have got my gearing all wrong tho. Went 53-39 with 11-28. Next year in looking to go compact with 11-32


Hard to tell the gradient, but yeah - you were almost certainly gear constrained and had no choice but to grind a super low cadence or go over your power target.

If you’re really into optimizing and have that TT/tri mentality you could experiment with a 53/34 to be able to spin uphill without giving up too much on the downhills. Definitely something to work out well ahead of the race though as that kind of range will take a lot of tuning


trpnhntr’s got it. I think too many of us triathletes think there’s nothing we can do about hills, but gearing… gearing… gearing… play around with it - compact, 30 in the back, whatever, but while you might not nail a 1.02, 1.44 and your legs are toast on the run.

Then I think you need to set a cap on power during sustained climbs. That is, a certain power you won’t exceed unless you absolutely have to because you’re out of gears. This is probably close to threshold, maybe 10-20% over… and it’s not something you’re sustaining. It’s there to get you over humps, make a pass, whatever, and that’s it.


Have a screen on your bike computer without speed on it. Our pride/ego makes us dig too deep to maintain a certain speed or not be passed by people - me included!. When climbing your power number is king, I typically have 3 or 5 second power showing. It can feel painfully slow but if your target is, for example, 180w for the ride then that number is doable both on the ascent and descent when the ego is taken out of it.

One way to train this? TrainerRoad’s outdoor workouts. Do long sweet spot intervals outside on rolling terrain and you’ll quickly get used to how seemingly easy you go on climbs and seemingly hard on descents in order to stay closer to target power throughout (and lower both VI and TSS in the process).

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This is another GREAT tip.

My long course tri bike leg screen has 3s Avg Power, NP, and distance, and that’s it. I turn all of my other screens off. You can set a watch for fueling, or if you know roughly when you’ll hit certain mile/km markers, you can fuel by distance. I actually did that during one relatively flat 70.3 and it worked really well.

For me, taking the results (time and speed) out of it really helps me make sure I’m sticking to my race plan.

It will be another 6 months before I back outdoors :rofl:

I suppose you could find some heinous hilly course on Zwift and practice TT pacing and try different ratios. Couldn’t hurt!


Yorkshire TT races this week…

Heinous is a good description.

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