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Differences between power TSS versus hrTSS
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Northy
Apr 27, 21 13:48
Post #1 of 6 (2487 views)
I picked up a new watch a few months back and have been recording indoor rides simultaneously on Zwift and the watch. Both Zwift and the watch pick up heart rate from the same hrm (a Polar H10, which has 2 BTLE connections) and Zwift also picks up power from the trainer (Saris H2). After the ride both the watch and Zwift upload to Training Peaks, and I simply delete the TP workout data from the watch since it only has hr and no power.

Why am I recording on both if I just delete the watch data anyway? Because the watch is also Polar and I'm curious to see whether Polar's "cardio load" is meaningful or actionable. Anyway...

One thing I've noticed is that if I ride aerobically or harder (i.e. tempo, sweet spot, threshold, vo2) the TSS training peaks calculates based off power from Zwift is greater than the TSS calculated based only on heart rate from the watch. If I ride super easy the opposite is true. For example:

• Friday 90 min aerobic ride, IF=0.68 based off power, TSS = 71
same 90 min ride hr data from the watch, IF=0.60, hrTSS = 62

• Sunday 2hr ride with 3x20 SS, IF=0.79 based off power, TSS = 124
same ride using hr from the watch, IF=0.69, hrTSS = 107

• 60 min recovery spin yesterday, IF=0.43 based off power, TSS = 19
same ride using hr from the watch, IF=0.60, hrTSS = 41

If I'm trying to keep track of overall training stress does it make more sense to keep the TSS calculated based on power for recovery rides, or use the hrTSS number? I've seen training peaks recommend using hrTSS for hilly trail runs where pace isn't a good reflection of effort. Is this a similar kind of thing with easy rides?
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Re: Differences between power TSS versus hrTSS [Northy] [ In reply to ]
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burnthesheep
Apr 27, 21 14:59
Post #2 of 6 (2463 views)
Northy wrote:
One thing I've noticed is that if I ride aerobically or harder (i.e. tempo, sweet spot, threshold, vo2) the TSS training peaks calculates based off power from Zwift is greater than the TSS calculated based only on heart rate from the watch.

I got into this rabbit hole a year ago with only having HR on my gravel bike/cross bike rides. I'd get astronomical TSS's based off some long tempo rides. Just cruise at a few BPM above Z2 for a few hours.

I wound up getting a meter for that bike.

HR is not only very personal for person to person but also very variable day to day and ride to ride. HR TSS would be laughably higher for me on the TT bike than power TSS due to the constricted riding position.

When I realized that, I figured I had to keep it all in the family in one activity. I was OK having a different activity type drive TSS and then I could dial my HR zones better for that activity type. Like, I'm a cyclist but run for cross train effect. Since I'm far from elite.

I'd do that. Try to get a meter on all the bikes, or a meter you can move.

Running rTSS vs HR TSS for me can be laughably off for me. I go by rTSS simply because it reflects how I feel from the effort better. I realize totally the aerobic effect is NOT that high for the run. But it gives a better "stress" and "form" to look at for planning purposes.

It may take some working out your HR zones in that watch better to get it closer to the power TSS if you care to.
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Re: Differences between power TSS versus hrTSS [Northy] [ In reply to ]
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indianacyclist
Apr 27, 21 15:02
Post #3 of 6 (2459 views)
Power is power. HR can change for tons of factors.

Use power where possible
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Re: Differences between power TSS versus hrTSS [indianacyclist] [ In reply to ]
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Northy
Apr 27, 21 16:33
Post #4 of 6 (2417 views)
Yes power is power and hr is influenced by all sorts of factors. But it's been consistently the case that for rides above ~55% FTP TSS is higher than hrTSS and for rides below ~50% FTP TSS is lower than hrTSS.

Phrased a different way, is it possible for heart rate to become a better estimate for training stress than power during very easy rides (especially given the exponential relationship between IF and TSS)?

A hypothetical example – let's say I do a long easy spin at a steady 100W for six hours. Based on power numbers that would be a total TSS of 58 for the 6 hour ride. A TSS of 58 ain't much for what amounts to (for me) a 2200 kJ ride.

My heart rate wouldn't get very high at 100W either, but it could easily be around double my resting heart rate. For a ride like this I wonder if heart rate would give a better estimate of training stress than power does.
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Re: Differences between power TSS versus hrTSS [indianacyclist] [ In reply to ]
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brasch
May 2, 21 13:38
Post #5 of 6 (2302 views)
indianacyclist wrote:
Power is power. HR can change for tons of factors.

Use power where possible

I usually use power as Well, button my commuter there’s no power meter. I usually get higher hrTSS than TSS. If HR zones are set correctly, I would argue that the hrTSS would be more correct. As HR changes for various reasons, so does you day to day ability to perform. The power IF is from a test at one point. Maybe your body knows better what kind of stress you put on your body?
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Re: Differences between power TSS versus hrTSS [brasch] [ In reply to ]
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burnthesheep
May 2, 21 15:25
Post #6 of 6 (2278 views)
brasch wrote:
indianacyclist wrote:
Power is power. HR can change for tons of factors.

Use power where possible

I usually use power as Well, button my commuter there’s no power meter. I usually get higher hrTSS than TSS. If HR zones are set correctly, I would argue that the hrTSS would be more correct. As HR changes for various reasons, so does you day to day ability to perform. The power IF is from a test at one point. Maybe your body knows better what kind of stress you put on your body?

Going downhill and around corners your power TSS accumulation nears zero. HRTSS still accumulates in that scenario and decreases as your HR recovers.

If you have say 7% power in a ride at under 50w you likely would see perhaps 5% more HRTSS than power TSS. For example.

Flatter and more nonstop the route, closer they should be.
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