It could be muscle recruitment. More posterior input, and potentially greater fatigue due to a lower cadence.
This isn’t related to flats vs climbs, but I am terrible out of the saddle. RPE is two fold at any given wattage and my legs start burning much sooner than if I’m sitting.
The grade changes the pedaling dynamics and recruits different muscles. The steeper the grade, the more pronounced it is. Similar effect on a trainer with a high flywheel effect vs. one with no momentum. I know some folks can do more power climbing, I’m just not one of them despite working on it a lot. Probably a byproduct of my early years cycling where I avoided any events (or training) that had hills and focused on TT power and was always a break-away power rider. Rolling gravel races are my thing.
Great example is my last 2 saturday workouts. Last week was rainy, so forced to do a 4+ hour trainer ride. Pretty challenging Zwift group ride that requires a constant tempo effort holding 250w+ for the entire ride (but pretty steady and smooth). Contrast that with yesterday’s outside ride where I’m training for leadville and doing steep hill repeats. Holding tempo on the climbs (250ish) doing repeats on a ~12 minute climb with 4 minutes rest between climbs. Perceived exertion much higher and I started cramping after less than 3 hours of that (with normalized power ~20w lower than my prior week’s ride with all the rest time between climbs). Cadence is a little lower climbing, but I’m training on my MTB and still spinning up the climbs at over 70rpm. I’m not going to struggle putting out power on a single 10 minute climb (even though it feels harder than the flats), but the legs will start failing when an event requires hours of steep climbing.
It’s not for lack of trying. I’ve been doing Leadville every year for the past several years and I’ve become a decent climber. This time of year, I’m typically climbing 20k+ feet per week and have done almost 400k feet of climbing since the start of the year. But it’s still a relative weakness compared to my power on the flats and I doubt I’ll ever be at the pointy end of a race that is dominated by long steep climbs.
Off road is a bit different because it’s often steeper and traction is a problem so you may need different cadence and muscle groups. On road though, if you can hold a wattage on the flat and have the gearing to keep the same cadence, I can’t see why you could not hold the same wattage on a climb.
Almost all my MTB training happens on the road. There just isn’t good climbing on dirt available nearby. But some of the roads are pretty steep (over 20% grade in places) and the same issues apply (just to a lessor extent vs. really steep dirt stuff).
Agree with @grwoolf - I think it’s primarily body position that drives it, although more airflow you get with speed on the flats helps too. I’m not super heavy (~80kg) but not a light climber either.
The only climbs I have near me are ~3-4 minutes max without driving or riding an hour so I really focus on doing extended intervals on the flats where I try and keep myself in more of an “attack” or climbing position which I think helps.
I think the point of really steep off road forcing a change in body position is true though. Get a steeper loose climb and I have to shift weight rearward to keep enough traction on the rear wheel, but those climbs are a pretty rare occurrence in the grand scheme of things (e.g. Leadville, maybe only the top of Columbine?)
IMO, the specificity of doing intervals on climbs to get better at climbing is approaching the marginal gains area of training. If you have a really important event coming up that you want to eek out every percentage you can then maybe consider getting on your trainer, propping up your front wheel to the desired grade, and then either upping the resistance or riding ERG mode with a low cadence. But for most people, just ride with what you got.
I spent the last 3 years in a hilly area but with the longest climb being like 4 minutes. But we did have a road by a river that was ~9-10 min long and a ~4.5min flattish loop around a park. I did 90% of my intervals on those flat roads.
But for your questions:
) level and I never did any VO2s during my blocks over 3 minutes with the exception of a 4min or two. Would 5min have been better? Idk, but I got good gains with 3min.Doesn’t look like it’s available any more but there used to be Hands-on: The AIRhub Pro Resistance Wheel | DC Rainmaker