Clyde1820

There's a reason it's called perceived effort and not actual effort. A lot can vary from one run/ride to the next. Breathing, form, temperature, differences in elevation changes in comparison to when/where along the route we hammer it, etc. Watts versus RPE, IOW.

Back when I used to run hard, years ago, I often noticed that on cooler days when well-hydrated it was possible for me to run extremely hard on a hard route/course while still keeping pulse rate lower than on a typical hard run. I'm pretty sure environmentals and hydration can affect things. Might well be better tied to, oh, deeper breathing, less-efficient form under certain loads, and whatnot. ("Apples to apples" comparos might be very difficult to achieve, in practice, given all that can vary from one run/ride to another.)

I also used to notice that I could overheat more easily if my cadence skyrocketed due to a given route's requirements, as compared to outright elevation changes. But then, I was extremely strong on hills and "tougher" sections and never felt like I needed to max-out on the tough stuff, whereas I most definitely felt that I had an upper limit to my cadence before it'd start getting me to overheat, overexert. RPE could feel like floating along on a "tough" course, but RPE could feel like a bear if my cadence went too high. "Grinding it out" (strength-wise) was always vastly better for my own perceived effort, on a given course, instead of boosting my foot speed and attempting to get more-efficient on that same course.

Don't forget: blood flow is about two things ... oxygenation/fuelling, and "air conditioning." And if the body doesn't have to work so hard at a given level of effort on a "standard" route due to being cooler, for example, then it should follow that the heart wouldn't have to pump quite so hard to stay in the zone. Perhaps less, too, if breathing more-fully and deeply, at a given level of work.

At the gym, there's an elliptical machine I occasionally use that has a program called "Constant Watts." It'll keep adjusting the resistance level on me to ensure the watts/output keeps within a narrow range. I burn vastly more calories (according to the machine's count) on the "Constant Watts" program than by simply goosing the difficulty and cadence myself. Though, interestingly, under the constant watts doesn't result in a noticeably higher average pulse rate than when I'm adjusting cadence and difficulty myself, despite the higher average watts and despite the much higher calorie count over the same amount of time. Anecdotal, sure, but ...

Can't say whether it'd translate to a bike, though I don't see why not.