As far as I can figure, a power meter's strain gauges' measurement of torque is no less a "measurement" than what a scale does to measure the weight of an object. Hang an object from a spring, make notice of how much the spring

It depends.

Metabolic and cardiovascular strain (and hence adaptation) will be (primarily) determined by the (temporally-smoothed) power output, regardless of how it is generated.

Neuromuscular demands (and hence adaptations in muscle contractile function) will be (mostly) dictated by the force and speed with which you pedal.

I developed quadrant analysis (QA) about 15 y ago as a way of visualizing the latter demands. QA was inspired, in part, by Robert's interest in torque vs. cadence plots and "power expansion pathways", but explicitly incorporates the physiological knowledge that significant type II motor unit recruitment seems to (initially) occur only at intensities above FTP. (The other motivation for QA was people's complaints that NP didn't seem to fully capture the stress they experienced during severely "on-off" cycling, e.g., a criterium).

Once dual-sided power meters that offered additional information about pedaling dynamics became available, I developed additional analytical tools, i.e., calculation of maximum effective pedal force (MEPF), gross power released (GPR), gross power absorbed (GPA), and kurtotic index (KI), all of which can be found in WKO4. This seems to be a bit of a deeper dive into cycling biomechanics than what motivated your original question, however.

A description of QA can be found in our book, as well as here (note that both the date on the article and the byline are incorrect):

https://www.trainingpeaks.com/blog/quadrant-analysis/

These sources describe the pedaling metrics unique to WKO4:

https://www.trainingpeaks.com/...and-metrics-in-wko4/

https://help.trainingpeaks.com/...ling-metrics-in-WKO4

https://irp-cdn.multiscreensite.com/...daling%20Metrics.pdf

TL, DR answer: specificity, specificity, specificity, specificity, specificity.

Pedantic, but I think those are both indirect. Measuring mass via a balance would be direct measurement. But measuring weight via a spring uses a calibrated correlation to material deflection. Like most power meters measure torque.

A beam balance must be calibrated as well. I really see no difference.

The difference is that with the balance no mathematical relationship between physical quantities is needed. It's comparing a mass to a known mass. Like using a measuring stick is comparing a distance to a known distance. However, like the torque arm formula need to convert a force to a torque. Or a formula to convert a material strain to a force.

This site may help.

Ok, so.....how does one measure power "directly?"

I don't know...torque wouldn't be too hard, but power would be tricky, from a bike.

thanks. let me read those articles and see what i can glean. i have a suspicion some riders would be well served by moderating their cadences more actively to lessen over-recruitment of type II fibers during exercise, even when there are fairly significant changes in power occasioned by the tactical realities of a race. also, that if that's true, that those athletes tend not to moderate their cadences sufficiently.

but i don't know. it's just a guess. a hunch. i'm exceedingly mentally, informationally, underequipped to extrapolate past that.

i need

why isn't torque a better measure of fiber recruitment than cadence?

... it occurred to me to ride - as a thought experiment - according to fiber recruitment during the power phase of the pedal stroke. or as close to fiber recruitment as i could get to it.

cadence is sort of the inverse of that. torque speaks directly that.

Metabolically, knowing your torque or cadence is not particularly helpful, while knowing power most definitely is ... Far better to focus on effort level and choose a gear appropriate for the situation.

Torque is a red herring.

RChung is a red herring.