I won’t argue with KJs and TSS, but miles… One mile on my single speed mtb, and one mile on my gravel bike (not even a road) are nowhere near comparable. Time makes way more sense here.
Edit: While we are at it 
I don’t have power meters on any of my outdoor bikes, therefore KJs/TSS go out of the window and time is basically all I have left 
I assume this is in regards to the latest Empirical Cycling podcast?
If so they were very clear they were basically only talking about easy riding
I’d go as far as to say TSS is not a complete metric for MTB. Going down a high speed technical decent is certainly more “training stress” than coasting a straight downhill on the bike path. But both are classified as “coasting.”
Recently I did some riding on REALLY muddy, twisty trails. Lots of small ups and downs with constant turning. Average power was low as I was constantly dodging trees. Average power and TSS were low but the training demand/stress was high.
Considering how many riders you see with badly fitting helmets (so they need to use a cap under it), I suppose their gloves do not fit well either.
Or when mucking around on a pump track. When I did that, HR was up but power was down. And I was worked! But I am a weak roadie. 
Made me think in that situation that HR was a better indicator of stress than power.
[Edit: yes, I took my road bike on a pump track. It was fun to just play bikes & I was conscious about not pedalling on crests.]
I’m not going to say that TSS is perfect, but you have two very different scenarios and are only pointing to a metric that accounts for part of the second scenario. Accumulated TSS or Load over Time would be a more wholistic metric.
You’ve got data and a spreadsheet. Invent something that you think is better and present it in a new thread here.
Unless you’re Allen or Coggin, I don’t really see any good reason for this kind of response. Be excellent to each other.
Just because you can identify the flaws in an idea doesn’t mean you have the background or expertise to develop something else.
I long ago recognized the issue @wintermute highlights above…surely the training stress accumulated for a mile of riding at mile 85 is not the same as the stress accumulated at mile 5. IIRC, even Coggan recognized this inherent flaw. But I would have no idea how to develop a “better” system, even though I have “data and a spreadsheet.” I don’t have the background in exercise physiology to do so.
Depending on your body shape, flexibility, etc. it may take 40mm of spacers to fit you perfectly. There seems to be an assumption that a bike that fits perfectly must have zero spacers. This is clearly nonsense unless everybody gets a custom frame or all bodies have the same dimensions.
Miles is terrible, and hours is only terribly discouraging if you can’t consistently ride 15-30 hours/week Hours is a simple first principles metric on the easy heart muscle and leg muscle contractions (and implied low autonomic stress and possible glycogen recovery from riding below LT1) that are the foundation of endurance conditioning.
Agree that “miles” is pretty terrible, but at least it’s somewhat of a function of both intensity and duration (along with a bunch of other stuff like wind, surface, elevation change, etc.). Hours tell you much less. You can ride a bike for an hour at a pace that is much easier than walking and only a few ticks above sitting on the couch. Or you can ride super hard for an hour and be completely wrecked. As a measure of training volume, I’d just argue that miles is less terrible than hours. Knowing available hours to train is important for budgeting time, but it’s not a metric that you’d use to ramp/track training with any degree of accuracy.
I also agree with the comments on TSS being imperfect, but it’s decent and that’s what I use to managing my progression. Besides being a better choice than hours, miles, or Kj’s, many of the mainstream tools for managing progression lean on TSS (with corresponding CTL and stress balance) as the primary metrics.
FWIW I have tracked kJ work and hours for 7+ years. And CTL/TSS/IF. You know what correlates the most to my fitness ups/downs? Hours and amount of threshold work. I’ve spent 3 years analyzing my data back and it couldn’t be more clear for someone that never averaged more than 8 hours/week over a year.
If you haven’t heard it, checkout an interesting Empirical Cycling podcast “Perspectives #34: Quantifying Training Volume, with Marinus Petersen” published June 9th.
My latest unpopular opinion (and data) is that mostly riding easy by rpe, on as little as 5-7 hours/week) is better for both health & performance. I’m retirement age, a desk jockey with very little endurance experience. Now if you only care about performance, well I have some thoughts and data about that too. But the performance only focus left me with signs of a haywire heart and a body that started slowly breaking down.
Yep, there is a big difference between exercising for health reasons and optimizing performance. They are at odds with each other once you get beyond a reasonable level of fitness. It’s all better than sitting on the couch watching TV with beer and pizza, but training at a very high level for performance is generally not beneficial to your health. For folks who aren’t paid to race their bikes, the risk/reward of training on the the hairy edge for months at a time to squeeze out a little more performance is pretty stupid. But here we are…
training for health and performance aren’t that far apart, however there is a lot of well intentioned but misguided info just a search term or ChatGPT click away.
I think you’ve misunderstood my response. No snark intended. There are lots of metrics kicking around (Garmin, intervals.icu, TSS, CTL, etc). If somebody thinks they these are not meeting their need, I encourage them to poke around and see what they can come up with that works for them (KWh/week, heartbeats per day, whatever they like). All metrics are abstracts, so nothing has to be (or will be) perfect. We are not talking about publication-quality research - just finding something that works for an individual. If they don’t have the skills themselves, starting a thread on “what would be a better metric for longer periods?” would be place to start.
@wintermute - Apologies if my post came across as snark.
I feel so seen 
Rather than measuring what truly matters, we tend to pull together data that is readily accessible without stopping to ask what we need to be measuring and how the insights will help move our business forward.
What we’ve found is a bit unsettling to data scientists: some of the things organizations currently measure are largely irrelevant or outright useless – and can even be misleading
I think we’ve all got spreadsheets 
First you need to ask why, what is it that you are trying to understand and for what purpose.
IMO we want to understand how much training we are doing in order to support established training principles;
To me, that means you must have a metric beyond time, there has to be elements of attributes of the training to be an effective measure
Someone posted upthread that any given cycling week or training tends toward a 0.6-0.7 IF, so if you add that as an assumption to your time measure of volume then at least you have something,
At the other end of the spectrum you could have a break down of time in zone, power and heart rate, some kind of measure of skills training (time in aero, complexity of descents), I’m sure you could really go to town.
In the middle I’m starting to suspect that kJ is a good all round measure of how much training a person has done and easily lends itself to planning for progressive overload and consistency. Also as an indicator of over training maybe as a percentage. Also lends itself easily to multisport.
It has limitations, of course; it doesn’t describe aerobic/anaerobic for example.
Sacrilege!
Step 1 is understanding the fundamentals of what drives improvements in performance, step 2 is collecting data, and step 3 is doing experiments over appropriate timeframes and having a good analysis tool.
Cart before the horse. My interpretation of the last 100 years of endurance science differs from yours. And I have multi-year data that I believe appears to prove my understanding is correct.
FWIW I agree with this guy:
and world-class coaches that share that view, like this one: Is Adaptive Training Gaslighting Me? - #5 by WindWarrior