This has probably been asked and answered many times but…
I check normalized power all the time after a ride to gauge my effort, and also check average HR.
How come normalized HR isn’t a thing?
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Your thinking is backwards.
Think about why power needs to be normalized.
Now think about why heart rate does not need to be normalized.
Hint: power goes to zero a lot
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The purpose of normalized power is to give you a measure of the unevenness of your power distribution (when you compare it to your average power). That is because power spikes take something out of you, and it will increase your recovery. Power can fluctuate wildly from one second to the next (go from mellowly riding along to an all-out sprint).
Heart rate changes slowly, i. e. you need a sustained effort to push up your heart rate. A 2-, 3-second spike in power will not cause your heart rate to spike. What that means is that the physiological cost to your body is well-approximated by your average heart rate (over a given efforts), not “normalized” power.
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Good question. I don’t know the answer.
Sorry but this is just not even remotely close to the truth. Last week I just did 5 x 3m vo2, with a bit of easy zone2. Avg HR 140. This is the same average HR that I would get with a Low Tempo ride, but the spikes profile and the physiological cost are completely different.
I have a very reactive HR, goes up and down fast with hard efforts, perhaps other people are different and the lack of homogeneity in HR response explains why it’s not normalized.
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My .02 - I think normalized power exists due to coasting which brings down your average. Even when coasting your heart is still beating so the average is a better representation of the work done. Time in zone might be more useful when talking about HR.
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You are missing the big issue and that is: Avg HR for a session does not appropriately describe the effort. See my example of 2 diff workouts.
Normalization is a generic time series procedure, you can select the appropriate parameters that would make the desired output meaningful.
The gist of op’s question, is why isn’t there a descriptive metric analogous to NP to capture the variable nature of HR. As I said before, I think it’s because HR as in bpm variance is different scales for different individuals.
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My heart rate is self-normalized. And if my heart drops out, I’m not gonna give a farq about my activity data.
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mmm. You don’t understand normalization
It has to do with the stochastic nature of power compared to HR, as almost everyone has alluded to.
I asked a similar question a few years ago (can’t find it right now. see below, @mcneese.chad found it), and someone proposed assessing the variability of HR during a single session using standard deviation. Obviously HR never goes to zero (so no need to normalize using a calculation similar to power) but it can vary in a hard group ride, long ride with variable efforts (hills, etc), races, stops, etc…and those are different than just “hold % HRMax for 3 hrs” (for example), even though the average HR for all of those can end up being the same.
Also, even though normalized power is very useful, it’s still not strain. It is a measure of load (when considered over time). That’s only part of the picture. As imperfect as HR is, it’s basically all we’ve got (can’t measure cardiac output). So having a crude metric for how variable it was is better than nothing.
- Is this it?
- Variability Index For Heart Rate
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That’s it
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going back to basics, the guy (Dr Andrew Coggan) that created normalized power wrote a paper for a USAC coaches meeting. He gave a background, justification for levels, and when it came to analyzing power data he outlined limitations of using kJ work and time in zone (frequency distribution of power).
His alternate approach was to leverage Dr Eric Banister’s TRIMPS work which for HR is duration x average HR x HR-dependent intensity weighting factor. So if you want a HR approach, go down the Banister TRIMPS path. I’ve never looked into the HR intensity weighting factor.
Does anyone know how TRIMPS works w.r.t. HR intensity weighting factor?
FWIW TrainingPeaks has a TRIMPS based TSS score - tTSS - that appears to only use duration and average HR.
The TP hrTSS uses duration, average HR, and threshold HR which appears to be a nod to using some form of intensity weighting.
Not the global average, the average during the interval or set (when you do 30-30s or so).
It is still reacting much more slowly and represents the average effort of your cardiovascular system within the last minute or few minutes. That means a weighted average of your heart rate will be not too different from the average, especially if you are looking at shorter durations.
Instead, time-in-heart-rate zone or heart rate in power zone will likely contain more useful information.
Is it even useful to look at normalized power for a whole ride?
I was actually just reading Racing and Training with a Power Meter the other day and the example they gave was looking at the normalized power of a 1 hour criterium or a 40k TT.
Yes, definitely, but you have to know why you want to look at it.
- On endurance rides it tells me whether I have been naughty or not. On good days my variability index is close to 1.
- In road races it gives you an indication how efficient you were.
- It gives an additional indication how hard a ride was. E. g. you could have a climb that is littered with small kickers, and if I punch it every time, that will show up in the data.
- Of course, you can also analyze segments. E. g. I always have to get out of town and get back into town. I made it a habit of pressing the lap button before that so that I can factor out these bits where I am typically limited by traffic patterns and it’d be stupid to send it at every traffic light.
for any geeks out there, open to page 100 of Dr Skiba’s Scientific Training for Endurance Athletes and big surprise, the TRIMPS HR intensity weighting factor is based on HR vs lactate curve. Big surprise because Coggan was inspired by Banister’s 1970s TRIMPS, and so the intensity weighting factor for power is based on power vs lactate curve.
No I don’t think so. Both Coggan and Skiba give reasons why its not. And why physiological cost is better approximated by power and ftp/cp (or pace and critical speed for runners), and its all built off the Banister TRIMPS HR based work from the 1970s.
Maybe this is a typo and you meant hrTSS, but rTSS is runTSS and is based on threshold running pace and normalized graded pace.
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yes, tTSS is TRIMPS TSS. And fixed it above in the original post. Sorry for the error! The letters r and t are next to each other on my keyboard.
There are a few variants of TRIMP, though the one you’re most likely to see in software is the exponentially-weighted form:
TRIMP = sum(t * h * 0.64^(k*h))
where t is time in minutes, h is fractional heart rate reserve, and k is a constant (1.92 for men, 1.67 for women)
This has some nice mathematical properties that TSS doesn’t. The derivative w/r/t time is just
dT/dt = h * 0.64^(k*h)
so individual bits of the workout just sum / integrate naturally.
You could certainly define a “normalized heart rate”. For an activity, compute the TRIMP for the whole activity and then find the heart rate N such that you would get the same TRIMP if your heart rate was a constant H for the whole workout. That is basically analogous to normalized power.
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