What is actually stored in the HR channel of profile 4?

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BillOsler
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What is actually stored in the HR channel of profile 4?

Post by BillOsler »

While puzzling over some of my recent test results I had a thought regarding a potential error.
The Garmin Connect iQ app displays a rolling 90 second CdA calculation.
But what is actually stored in the Aeropod's HR channel? Instantaneous results? or a rolling average?
I thought about this as I rode on the hoods to the starting point of a CdA test (after my calibration ride on the clip-on extensions).
I went from the drops to the hoods a few seconds before I hit the starting point of the test.
For my calculation of the CdA estimate I averaged the HR channel results over the time spent doing the test.
That approach works fine if the Aeropod is storing instantaneous CdA estimates in the HR channel ... but the calculation of the CdA will fail if the Aeropod stores a 90 second average in the HR channel because a 90 second rolling average will not reflect accurately the CdA during a test that lasts only about 2-5 minutes. Too much of the test data would be diluted by the 90 seconds prior to the beginning of the test.
Velocomp
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Re: What is actually stored in the HR channel of profile 4?

Post by Velocomp »

What is stored is the same data that is displayed in the Connect IQ app (including the conversion constant).
John Hamann
BillOsler
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Re: What is actually stored in the HR channel of profile 4?

Post by BillOsler »

Velocomp wrote: Mon Apr 15, 2019 2:04 pm What is stored is the same data that is displayed in the Connect IQ app (including the conversion constant).
That being the case would it not be more accurate to discard the first 90 seconds of any effort used to calculate the CdA or alternatively use the Isaac CdA analysis instead of basing the calculation on the data in the HR channel?
Velocomp
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Re: What is actually stored in the HR channel of profile 4?

Post by Velocomp »

If you're changing positions then yes, for the first 90 seconds after the change the CdA is "blended" from your prior test. I would look at the CdA after 90 seconds.

The same principle applies if you've made a sharp turn.

Note that, if the test is long enough, these kind of short term effects blend into the background...
John Hamann
BillOsler
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Re: What is actually stored in the HR channel of profile 4?

Post by BillOsler »

Velocomp wrote: Mon Apr 15, 2019 6:16 pm If you're changing positions then yes, for the first 90 seconds after the change the CdA is "blended" from your prior test. I would look at the CdA after 90 seconds.

The same principle applies if you've made a sharp turn.

Note that, if the test is long enough, these kind of short term effects blend into the background...
I understand that from this perspective longer tests are desirable, though longer tests raise the risk that fatigue will become a factor affecting results.
If a sharp turn also introduces problems then that means for a typical out-and-back test the first 90 seconds of each portion are suspect?
My guess is that for an out-and-back test the best practice is to use the same stretch of road for both directions so in effect that means losing the first and last 90 seconds. A one mile (each way) out-and-back at 20 mph takes 3 minutes so the ideal course would be at least 2 miles each direction with fairly uniform pavement, no sharp turns, little/no traffic, no stop signs or railroad crossings and no really steep hills. Finding that ideal location may be harder than performing the tests.
Velocomp
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Re: What is actually stored in the HR channel of profile 4?

Post by Velocomp »

Another thing you can do is to touch the lap marker on your Garmin/Raptor at the end of each test. You will see, for about 10 seconds, the average CdA from the previous lap; then, CdA will go live again, at the current value, not the averaged value from the past 90 seconds.
John Hamann
BillOsler
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Re: What is actually stored in the HR channel of profile 4?

Post by BillOsler »

That's interesting ... so does that mean that if I have the Garmin set to auto-lap by position (as opposed to pressing the button) at the beginning and end of the section I want to use for testing then I don't have to worry about the prior section "poisoning" the test? I usually have it set up that way so I can focus on maintaining my position and power rather than watching for a specific time or location.
Velocomp
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Re: What is actually stored in the HR channel of profile 4?

Post by Velocomp »

Umm...I don't have a certain answer to that question, but I suspect the auto-lap feature will do as you suggest.

Let us know what you find out!
John Hamann
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