# Is HIE similar enough to W for this Garmin IQ data field?

Hi all,

Was interested in running this IQ field on my Garmin. Is HIE similar enough to W to make it interesting/usefuk to look at?

Hi Patrick,

W’ and HIE are similar in concept, but function (and are calculated) in different ways. In the CP/W’ model, the amount of W’ is fixed and is assumed that any effort performed to failure will result in W’bal = 0. In practice, this often results in maximal efforts that either force W’ to go negative or , if avoiding letting W’ go negative, W’ will be overestimated.

Xert’s measure of HIE is also a fixed value; however the useable amount of HIE will vary depending on your MPA. Almost always, MPA becomes your limiter before you consume/utilize all your HIE.

The best example I could show how/why Xert is different (better?) is to think about an athlete with a TP of 250 and W’ of 20.0 kJ (CP/W’ doesn’t know/care about a user’s peak power, but let’s assume that PP = 1000 W) and compare that to an Xert fitness signature of 250 W TP, 20.0 kj HIE, & 1000 W PP.

The traditional CP/W’ model would estimate that this athlete has 20,000 J’s to spend above threshold. If we used their model to estimate what was achievable for 2 min, the model would assume that they would expend 20,000 J’s over 120 s, which comes out to 167 W above TP for 2 min. So CP/W’ would assume that this athlete could achieve 250 + 167 W for 2 min (417 W).

However, since we know that MPA will become the limiter for this athlete before they can utilize all their HIE, Xert would estimate that this same athlete’s 2 min power would actually be 399 W, and that when they reach the point of failure, their HIE will not be 0 kJ’s, but that MPA would simply be equal to their 2 min power at that point. The farther up the PD curve you go, the more the two models will deviate. Hopefully that makes sense!

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