I’ll be doing Ironman Lake Tahoe September 22. We’ve started discussing the effects of altitude on training and racing at Endurance Nation. Here’s a set of comments I recently posted.
Since 2005, I’ve spent 2-6 weeks a year training for IMs at 5700-9600′ while living @ 8400′ outside Aspen, CO. Also, I’ve reviewed some literature about training and racing at altitude. Here are a few notes based on that.
Let’s start by noting that the elevation of the lake itself is 6200′. While the bike course does top out over 1000′ above that, most of the bike and all of the run is done at or near lake level. So 2000 meters is what we’re talking about (best to use metric as all studies are done on that basis.) At that altitude, atmospheric pressure is 20% less than at sea level. Since oxygen crosses into the blood stream across lung membranes mostly by being “pushed” by that pressure, and in part by being “pulled” by the lower concentration of oxygen in venous red blood cells compared to arterial, the effective oxygen in the blood stream at 2000 m is about 10-15% less than at sea level. That variance will depend on how much you are acclimated with increased red cell numbers, size, and blood volume, as well as some other physiologic changes which occur with living and/or training at altitude.
One article I checked out (from “Aviation, Space, and Environmental Medicine”, Vol 69, #8) reviewed a number of studies of athletic performance at altitude. Here’s a relevant quote: “…at 2000 m altitude, events lasting less than 5 min … would be minimally affected while events lasting 20-30 min … would be impaired by about 5%, and events lasting 2-3 h would be impaired by 10-15%.” There are a number of factors at work here, but most of us are probably just interested in the actual impact on performance and not the physiology behind it.
All that I have read, and my own personal experience, are consistent with the table Wm includes in his post. Eg, I have a standard TT I do up Maroon Creek Road, going from 8000′-9300′ over 6.7 miles at a constant uphill gradient maxing @ 7-8%. Takes me about 40-45 minutes. While I can’t do that at 100% of my sea level FTP, I con routinely do it at 85-90% of my FTP.
As to running, I checked back in my log and compared long runs within two weeks of each other of similar distance (within 1-2 miles same distance, greater than 13 miles), done at altitude and at sea level. All were 10-30″ (30″ >> 6%) slower at an altitude of about 6500′ compared to 200′ I think the truest difference is more like 30″, considering I do most of my long runs on a hilly course at home, and on a flat bike path at altitude. The most recent example bears this out. During my current marathon hack, I did two 18 mile runs two weeks apart, both on bike paths. At sea level, I averaged 8:16; at altitude, I averaged 8:48. So, again, at 2200 meters I seem to run about 5-6% slower over the same distance at similar effort levels at terrain, altitude compared to sea level. YMMV, as I am probably a very fit runner. Others newer to running or slower may have a greater decrement; someone younger and/or fitter may have less. But not a lot less.
My recommendation for Tahoe: use an FTP of 8-10% lower for biking (remember, you will get a slight advantage from less air resistance), and a run pace of 5-10% slower, depending on how strong a runner you are. Altitude is like heat: you can’t overcome it with will power alone. Like running up a hill or into the wind on a bike, you just have to back off as much as the environment demands.
Swimming is a separate topic. There’s not much data on this, and I don’t have long OWS experience of my own to compare. But I do know the biggest risk is starting out at too high of an effort level. You will probably NEVER recover from that during the swim.
Another effect of altitude to remember: the lower air pressure means dryer air. Which means faster insensible loss of water from the lungs, as well as sneaky sweating, meaning it evaporates before you realise your are sweating. So you need more fluid than you normally would for a given effort level at a given temperature. Also, part of acclimitization which you’ll experience immediately upon arrival is weight loss which is really dehydration. You’ll need to drink more than normal during your first 3-4 days after arriving at altitude.
Finally, less air means more sun radiation gets through. So sun screen is critical. And less air means less heat is retained when the sun is not shining. So a cloudy day will feel colder, going from sun to clouds will chill one, and when the sun goes down, it gets colder quicker.
Training at altitude is another topic entirely, which I can comment on if anyone is interested. Teaser: I believe there IS a benefit to training high, for low altitude events at least for LOOONG events like marathons and Ironman, but you have to know how to do it. For shorter runs and tris, I think it IS true that training at altitude is not a great idea. And, of course, training @ 6200′ for an event @ 6200′ makes some sense, again, if it is a long event. Not a good idea for sprinters or swimmers, though.