Thanks @jarsson
Nicest compliment you could give me 
I kind of agree, for everyday training. I think muscle oxygenation is like using a continuous glucose monitor: you can gain a ton of insight for the first two weeks of using it if you know how to, or you have someone who can interpret the data. But the marginal insight gained after that declines quickly. Maybe it would be better used by coaches who can rent out a NIRS sensor to their athletes for periods of time to ‘calibrate’ their training, then pass them on.
I agree, although I think this might be more important than you give it credit for: I also find muscle oxygenation correlates very well to perceived exertion & sensations. Which means, as above, that we can use NIRS to calibrate our sensations during low or high intensity training, without being beholden to watching the numbers.
But we have to understand what those sensations mean, and what sensations we should be targeting. SmO2 gives us another quantitative dimension (alongside power, HR, cadence, etc.) to contextualize our sensations. Then we can let our brains do the work of integrating all the signals and returning a wholistic feedback about the current effort. And If we respect those sensations, understand what our intended effort level is for the particular training session, and put our egos aside by not chasing numbers that don’t match, we’ll probably get more out of our training sessions.
I’ll give my basic actionable suggestions for using muscle oxygenation in practice. This advise is mostly assuming we’re measuring NIRS at the vastus lateralis of the quads. Responses will change at different muscles, of course.
Generally speaking, we can look at two parameters: (1) the percent saturation (SmO2) value, and (2) the rate of change. I’m not even gonna talk about THb right now, because that opens up a whole can of conflicting interpretations. The absolute Smo2 value is imprecise within ±5%, meaning a difference of 10% between legs, or between days, or between one minute to the next, isn’t really meaningful. Although as we use it more, we can narrow down what our own smallest worthwhile change is.
At low intensity I look at the value and try to keep SmO2 above a certain target, which is close to my physiological maxima (individually determined). Basically, the highest balance of power and oxygenation. This always forces me to ride at a much lower intensity than I expect, and I have to re-calibrate my perception of effort for low-intensity training quite often. This is because the goal of low intensity training is often to maintain a high perfusion of blood, O2, substrate, nutrients. (I’m not trying to be prescriptive here, just descriptive. The goals of low-intensity training will vary as much as anything else)
At high intensity I look more at the slope, or rate of change in SmO2. But also at min and max points. What profile I’m looking for depends on what I’m trying to accomplish with my intervals. We could be trying to repeatedly deoxygenate and reoxygenate across as wide a dynamic range as possible (lowest min, highest max) with repeated sprint training. We could be trying to maintain SmO2 at some target value for some long interval duration, without letting it creep down or up. We could be trying to drop SmO2 quickly, then allow it to creep back up to some target as gradually as possible by modulating power or cadence.
Lots of possibilities. But again, we need to understand, or we need to work with someone who understands the why, and can interpret the data to inform future training decisions. Honestly, at this point I think we’re mostly still making up the interpretations experimentally as we go along. Which is exciting, because the field is growing in multiple interesting directions. But it’s also why there aren’t yet established, systematic prescriptive guidelines for muscle oxygenation as there are for power or HR.
For more education, I highly recommend the Moxy Summit conferences over the past few years. The last two virtual summits are freely available. This is probably the most accessible source of actionable information around how researchers & coaches are using muscle oxygenation in practice. I gave a presentation this year. I especially recommend watching Dr. Brett Kirby’s talk this year, and his previous talk from 2017 (which I think is behind a paywall).
