Will the correct average HR please stand up?

General discussion on Training. How to get better on your erg, how to use your erg to get better at another sport, or anything else about improving your abilities.
HornetMaX
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Re: Will the correct average HR please stand up?

Post by HornetMaX » May 20th, 2024, 10:09 am

Sakly wrote:
May 20th, 2024, 9:30 am
No, it does not. You only get per-stroke data, if you use ergdata.
A running average will be computed in the most precise format the CPU can handle (not from the shown value of the PM display) , thus no computation errors like mentioned.
Yeah, I wrote it down (very) wrong, my bad. PM5 does not store per-stroke data. But this is an extra reason to compute the avg power from time and distance and the formula instead of doing a real average of per-stroke power.

Once you know the average pace, the formula gives you the average power. And for the average pace you don't need to do an average of per-stroke pace: you just get it from time and distance, by definition. Somehow like the average speed is typically not computed as "the average of instantaneous speeds" but, more simply, as total distance over total time.

You can check all this from any random logbook session. Take this (from the logbook):

Code: Select all

Time 	Meters 	Pace 	Watts 	Cal/Hr 	S/M 	HR
16:52.8 4,500m 	1:52.5 	246 	1145 	27 	178
5:35.9 	1,500m 	1:51.9 	249 	1158 	28 	174
5:37.5 	1,500m 	1:52.5 	246 	1146 	28 	179
5:39.4 	1,500m 	1:53.1 	242 	1131 	28 	181
First interval is 1500m in 5:35.9 gives you an average pace (for that interval) of (5*60+35.9)*500/1500 = 111.97 seconds, that is 1:51.9 (it truncates here ...). From that average pace you compute the average power as 2.8/((111.96/500)^3) = 249.35 W.

You can do the same for the 3 other intervals.

If you want the overall average power you do the same with the overall time and distance: 4500m in 16:52.8 gives an average pace of (16*60+52.8)*500/4500 = 112.53 s, or 1:52.5. And for the power: 2.8/((112.53/500)^3) = 245.6 (it rounds at 246 here).
1973, 5'8" (173cm), LW, started rowing Sep 2021 (after 10 years of being a couch potato), c2 log

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gvcormac
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Re: Will the correct average HR please stand up?

Post by gvcormac » May 20th, 2024, 8:39 pm

HornetMaX wrote:
May 20th, 2024, 8:29 am
gvcormac wrote:
May 20th, 2024, 8:21 am
This brings up a question that I've had on my mind for a while, but not yet investigated: How is average power (watts) calculated? Do they just apply the power formula to the average pace (either overall or per split)? If so, this is wrong.
Power [W] = 2.8/((Pace [s]/500)^3)

In words: take your average pace per 500m and convert it to seconds (e.g. a 1:52.3 pace is 112.3 seconds), divide by 500 and cube the result.
Finally divide 2.8 by that number and you have your avg power in watts.
I'm not sure what assumption you're saying is wrong. That averaging power is different from converting power to pace, averaging pace, and converting back to power? These give different results, for sure.

gvcormac
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Re: Will the correct average HR please stand up?

Post by gvcormac » May 20th, 2024, 8:54 pm

HornetMaX wrote:
May 20th, 2024, 10:09 am

Once you know the average pace, the formula gives you the average power.
Not so. Here's a simple example.

Suppose I row for two minutes at 2:00 pace and stop for two minutes. The average power is 101.25 watts. The average pace is 4:00.

Suppose I row for four minutes at 4:00 pace. The average power is 25.3 watts. The average pace is 4:00.

If you think "stopped for two minutes" is too contrived, try two minutes at 2:00 pace plus three minutes at 3:00 pace vs 5 minutes at 2:30 pace.

Sakly
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Re: Will the correct average HR please stand up?

Post by Sakly » May 20th, 2024, 11:30 pm

HornetMaX wrote:
May 20th, 2024, 10:09 am
Sakly wrote:
May 20th, 2024, 9:30 am
No, it does not. You only get per-stroke data, if you use ergdata.
A running average will be computed in the most precise format the CPU can handle (not from the shown value of the PM display) , thus no computation errors like mentioned.
Yeah, I wrote it down (very) wrong, my bad. PM5 does not store per-stroke data. But this is an extra reason to compute the avg power from time and distance and the formula instead of doing a real average of per-stroke power.

Once you know the average pace, the formula gives you the average power. And for the average pace you don't need to do an average of per-stroke pace: you just get it from time and distance, by definition. Somehow like the average speed is typically not computed as "the average of instantaneous speeds" but, more simply, as total distance over total time.

You can check all this from any random logbook session. Take this (from the logbook):

Code: Select all

Time 	Meters 	Pace 	Watts 	Cal/Hr 	S/M 	HR
16:52.8 4,500m 	1:52.5 	246 	1145 	27 	178
5:35.9 	1,500m 	1:51.9 	249 	1158 	28 	174
5:37.5 	1,500m 	1:52.5 	246 	1146 	28 	179
5:39.4 	1,500m 	1:53.1 	242 	1131 	28 	181
First interval is 1500m in 5:35.9 gives you an average pace (for that interval) of (5*60+35.9)*500/1500 = 111.97 seconds, that is 1:51.9 (it truncates here ...). From that average pace you compute the average power as 2.8/((111.96/500)^3) = 249.35 W.

You can do the same for the 3 other intervals.

If you want the overall average power you do the same with the overall time and distance: 4500m in 16:52.8 gives an average pace of (16*60+52.8)*500/4500 = 112.53 s, or 1:52.5. And for the power: 2.8/((112.53/500)^3) = 245.6 (it rounds at 246 here).
Really, I don't get your point.

As I wrote - pace, power, cals, distance can be converted into each other, so you only need to calculate a single one of it and use the formula to show the others.
But I don't get the link why you think this has anything to do with calculation of a running average. This is a metric of the PM, so you need to calculate it at every stroke, otherwise you can't show it! :)
Male - '80 - 82kg - 177cm - Start rowErg Jan 2022
1': 355m
4': 1217m
30'r20: 8068m
30': 8,283m
60': 16,222m
100m: 0:16.1
500m: 1:27.1
1k: 3:07.8
2k: 6:37.1
5k: 17:39.6
6k: 21:15.3
10k: 36:01.5
HM: 1:18:40.1
FM: 2:52:32.6
My log

jamesg
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Re: Will the correct average HR please stand up?

Post by jamesg » May 21st, 2024, 1:29 am

Once you know the average pace, the formula gives you the average power.
So one would hope, given that the PM measures Work done per stroke, and calculates everything else from that. That's why the machine can be and is called an ergometer.
08-1940, 183cm, 83kg. Last seen MHR 140.
2024: stroke 6 W-min @ 20-21. No times yet, now using WODs.

iain
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Re: Will the correct average HR please stand up?

Post by iain » May 21st, 2024, 3:55 am

jamesg wrote:
May 21st, 2024, 1:29 am
Once you know the average pace, the formula gives you the average power.
So one would hope, given that the PM measures Work done per stroke, and calculates everything else from that. That's why the machine can be and is called an ergometer.
You would have thought so, but when an interval includes very different paces then it seems to convert the average pace, as pace is not directly proportional to power, this will be different. That said, for most splits at broadly the same pace the difference is tiny. I suspect that nothing has been changed to maintain comparability to earlier PMs. I am with Sakly that Ergdata fills the gap for those with PM5s, I a happy with the data from my PM3 and not inclined to upgrade it. Many other companies might have been tempted to upgrade to make the older monitors demonstrably less effective to sell more PM5s eg by downloading more data to logbook and conspicuously leaving this unentered from those downloading from PM4s and earlier!

Re data stored, my biggest bugbear is the loss of data on "Just Row". Real time you are shown data for every 5 min. But if the row exceeds 35' it takes the simple average (or for totals, the sums) of consecutive splits, again when you exceed 65'. I know a very small proportion of rowers row over 35' and we can set up to have this data, but I like the simplicity when doing an adhoc row, W/up or C/D of "Justrowing" and periodically get caught out when inadvertently exceeding these limits.
55, lightweight in pace, trying to get back to Lwt by gravity. Currently training 3 times a week after a break to slowly regain the pitiful fitness I achieved a few years ago. Free Spirit, come join us http://www.freespiritsrowing.com/forum/

Sakly
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Re: Will the correct average HR please stand up?

Post by Sakly » May 21st, 2024, 4:40 am

iain wrote:
May 21st, 2024, 3:55 am
jamesg wrote:
May 21st, 2024, 1:29 am
Once you know the average pace, the formula gives you the average power.
So one would hope, given that the PM measures Work done per stroke, and calculates everything else from that. That's why the machine can be and is called an ergometer.
You would have thought so, but when an interval includes very different paces then it seems to convert the average pace, as pace is not directly proportional to power, this will be different. That said, for most splits at broadly the same pace the difference is tiny. I suspect that nothing has been changed to maintain comparability to earlier PMs. I am with Sakly that Ergdata fills the gap for those with PM5s, I a happy with the data from my PM3 and not inclined to upgrade it. Many other companies might have been tempted to upgrade to make the older monitors demonstrably less effective to sell more PM5s eg by downloading more data to logbook and conspicuously leaving this unentered from those downloading from PM4s and earlier!

Re data stored, my biggest bugbear is the loss of data on "Just Row". Real time you are shown data for every 5 min. But if the row exceeds 35' it takes the simple average (or for totals, the sums) of consecutive splits, again when you exceed 65'. I know a very small proportion of rowers row over 35' and we can set up to have this data, but I like the simplicity when doing an adhoc row, W/up or C/D of "Justrowing" and periodically get caught out when inadvertently exceeding these limits.
As far as I know the old ergdata version can also be used with PM3/4 (cable connection based), so will give you some (many!) of the metrics like the new Ergata and PM5.
The only thing I know of, which is different in reported value/metric in the new Ergata app is the real HR average of the whole piece.

I also use just row from time to time, when I'm not sure how far I want to go. I realized that the 5min splits change to 10min splits in the summary afterwards as soon as you pass the 60min mark. During the row the 5min splits and their metrics are shown by the PM5 the whole time. So this seems to be a difference between the older and newer PMs.
Male - '80 - 82kg - 177cm - Start rowErg Jan 2022
1': 355m
4': 1217m
30'r20: 8068m
30': 8,283m
60': 16,222m
100m: 0:16.1
500m: 1:27.1
1k: 3:07.8
2k: 6:37.1
5k: 17:39.6
6k: 21:15.3
10k: 36:01.5
HM: 1:18:40.1
FM: 2:52:32.6
My log

HornetMaX
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Re: Will the correct average HR please stand up?

Post by HornetMaX » May 21st, 2024, 8:51 am

Sakly wrote:
May 20th, 2024, 11:30 pm
Really, I don't get your point.
No wonder, the stuff I wrote about average power was intended for the other discussion (with gvcormac), not for our one on avg HR. My bad.
1973, 5'8" (173cm), LW, started rowing Sep 2021 (after 10 years of being a couch potato), c2 log

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HornetMaX
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Re: Will the correct average HR please stand up?

Post by HornetMaX » May 21st, 2024, 9:25 am

For the average power discussion, yes gvcormac, what you say is correct: averaging power is different from converting power to pace, averaging pace, and converting back to power. Because the relation between power and pace is non-linear.

As pointed out by iain, for splits/intervals that are at constant pace the formula works, and if within a split/interval the pace variations are reasonable, the difference is likely small.

For fun, I just logged this session: https://log.concept2.com/profile/1528069/log/88390206

It's 2min @ 2:00 pace and 3min at 3:00 pace (roughly, it's hard to row precisely that slow).

The logbook shows this summary:

Code: Select all

Time 	Meters 	Pace 	Watts 	Cal/Hr 	S/M 	HR
5:00.0 	999m 	2:30.1 	103 	655 	21 	133
1:00.0 	250m 	2:00.0 	203 	997 	27 	147
2:00.0 	250m 	2:00.0 	203 	997 	26 	154
3:00.0 	185m 	2:42.1 	82 	582 	18 	133
4:00.0 	159m 	3:08.6 	52 	479 	16 	121
5:00.0 	156m 	3:12.3 	49 	469 	18 	114
The "Watts" for each 1min split agree with the ones you can obtain from the split pace and using the formula (e.g. 2:00 pace --> 203W).
Using the overall avg pace (2:30.1) and the formula you get 103W, exactly what the logbook shows as "avg Watts".

Taking the per-stroke data and time-averaging the per-stroke power, you get 117-118W.
Notice that averaging the per-split average power you'd get (1*203+1*203+1*82+1*52+1*49)/5 = 117.8W. Close enough. That's because within each split the pace was roughly constant.

So as iain said, the PM5 (and logbook) take a bit of a shortcut here too: the avg Watts they show for the session is computed from the session's average pace. This is correct only if the pace was constant across the whole session. Otherwise, it underestimates the average power.
jamesg wrote:
May 21st, 2024, 1:29 am
So one would hope, given that the PM measures Work done per stroke, and calculates everything else from that. That's why the machine can be and is called an ergometer.
Right. The PM5 measures stroke work, so it has per-stroke power and overall interval & session work.
However it seems the session avg watts is computed with the shortcut and hence somehow "wrong" (i.e. not the real average of the per stroke power).
1973, 5'8" (173cm), LW, started rowing Sep 2021 (after 10 years of being a couch potato), c2 log

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