My wife's family has a cabin inside the Rocky Mountain National Park and the elevation is about 9,100 feet. My runs are about 2 minutes per mile slower. After being there 3 or 4 days, I start to get sick. A couple days after that, I feel normal, but still run slow.

I was born and raised in Quito, Ecuador, this is 9.2k altitude. Now I live at sea level. And yes, the sole act of breathing is harder at altitude, at least much harder until you get acclimatized (2-4 weeks) when I travel there I usually I see 10 bpm more with similar effort than sea level, and I see 15-18bpm more when I go to the mountains above 15k ft.

It depends. I don’t feel like going from Denver to the mountains is bad we are at 6200ft. But coming from sea level it can be rough.

The hardest thing I noticed when I did a race from loveland 11k ft to Georgetown 8500 ft. Was that I was shelled really early. I was able keep my normal heart rate but with less oxygen my legs died quick. Fun race though lol

As is often the case, Joe Friel has a comprehensive answer:

https://joefrielsblog.com/...aerobic-performance/

I use the table there to discount power targets at altitude. Has worked well for me so far.

ETA: to answer the question you asked, going from 5000 ft to 10000 ft reduces available aerobic power from 93.7% of seal level to 84.4%. so it should feel roughly 10% harder for the same aerobic power.

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Darren
https://www.strava.com/athletes/12385497

So I was actually about to start my own thread on this, but as long as we're on the topic of altitude...

I've listened to a bunch of podcasts with sports scientists, but I'm curious if anyone has any experience with this aspect of it: Lets say my race effort wattage (~85% of FTP) is limited primarily by my muscular endurance rather than aerobic endurance. Of course they're tied to each other to a degree, but if I were to drop down to sea level will it feel easier to ride the same watts as at altitude/ride ~7% higher at the same aerobic level? Do the actual muscles benefit from more oxygen in the entire system basically, or am I still limited by what my legs have trained to do.

I certainly feel like power comes easier when I race at sea level having lived at altitude for most of the past 3 years, but it doesn't necessarily make sense to me.

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Benjamin Deal - Professional - Instagram - TriRig - Lodi Cyclery
Deals on Wheels - Results, schedule, videos, sponsors

I live at 900ft(Chicagoland).

I didn't find a 10k start with 13.3k peak any different than just beyond mile high.

Both made technical trail run descents more difficult as I couldn't mentally focus as my brain seemed foggy. Ascents seemed the same as I passed a lot of locals on the up, but was passed on the downs.

Overall it wasn't as bad as I expected. I did the "fly in and run the next day" vs. acclimatizing on pretty much all my altitude runs.

Yours is more of a training/living question so maybe my response won't help you.

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Swim - Bike - Run the rest is just clothing changes.

I rode on some of the Colorado Trail a couple summers ago.
Riding at 12,000' was a beat down for me. I'll admit I was regaining fitness after a long layoff, but it was noticeably different at that elevation versus 7,000'.

My N=1 is that the my FTP changes by 1-1.5% per 1000ft, so going up or down 1-2000ft isn’t really noticeable (less variability than day-to-day differences in fitness). Now after 2 hours of climbing in the neighborhood of my FTP up to the top of Mount Evans (14,000ft) the differences are brutal.

Was talking to a former pro about going from altitude to sea level.

I noted that it's so difficult for an altitude rider to adjust to the constant surges on crit and rrs because they simply don't get to train the much at altitude - recovery takes so much longer and we never get to 100% oxygen saturation in the first place. For instance, Superweek was famous for Colorado riders driving the break and then coming last in the sprint.

He made an excellent point - that PE gets messed up by all that extra oxygen, so that one feels like superman for a while and can go super deep for much longer than expected. By the time the pain kicks in it's too late and the rider is toast - damage done.