significance of being limited by legs or by heart/lungs

These days it often seems when I'm on a fast 30 mile ride that the limiting factor to my performance is heart/llung capacity - there's just a limit to the amount of air I can breathe over a sustained period. When I'm feeling on top form (and do my fastest rides) that often seems to be the case, but if I'm feeling tired for whatever reason it's usually the way the legs feel that is limiting. Also the fitter I get the more it seems the lungs are limiting rather than the legs. What's the take-home lesson from this in terms of training - e.g. do heavy legs mean you need a couple of days off?
0
Posts
Perceptions are funny things.
I've ridden PB power levels on days my legs felt like lead or a phrase that sometimes appears in my diary notes "leg like wood". On other days I'd have to wind it back, accept it was a bad day and crawl home.
For sustained efforts such as long TTs, then breathing shouldn't be a limiter, since by definition you are operating below your VO2 Max. Unless perhaps you are at altitude and aren't used to it.
But when you do get fitter, it is entirely possible you are operating at a higher percentage of your VO2 Max levels and can notice that.
What's the best way to increase VO2 max...?
By riding efforts at and around intensities that induce VO2 Max.
That is, a pace you could maximally sustain for ~ 4-6 minutes and repeat multiple times (4-8 times) with limited recovery (say 3-5 min in between).
But choosing when to do such training is important. I would hazard a guess that that is not an appropriate training focus for what you need.
On the 30 miles rides when I get going, I'm breathing fairly deeply and with a good rythym (it seems to help to sync it to my cadence, e.g. one breath for x number of revolutions). Sometimes my legs feel ever so slightly as if they could use more energy if they had it, like a very mild version of that feeling you get if you haven't eaten enough.
I guess I need to get less subjective and start measuring things properly.