Altitude Training and Acclimatization for a Mountain Ultra

The air up there still holds the same percentage of oxygen, but the pressure is lower, so every breath you take delivers fewer oxygen molecules to your blood. Your effective VO2max drops and any pace you run costs you more effort. Below about 3,000 to 5,000 feet you barely feel it. After that it picks up, roughly 2 to 3 percent of your aerobic capacity gone per 1,000 feet you climb. In real ultra terms that usually shakes out to about 3 to 6 percent slower at 5,000 feet, 6 to 10 percent at 7,500 feet, and 12 to 18 percent at 10,000 feet, where there is roughly a third less oxygen to breathe. And it is not just the aerobic hit. Altitude kills your appetite, it pulls more water out of you when you breathe, it wrecks your sleep, and it makes the hard climbs feel way worse than they should. That is why you run a mountain ultra by effort and forget about your sea-level splits.

Part of it comes fast and part of it comes slow. The worst of the acute stuff (bad sleep, headache, stomach problems, fatigue) hits over the first one to three days, and about half of that early aerobic loss comes back within roughly 45 hours as your breathing and fluids sort themselves out. The deeper change, more red blood cells and more hemoglobin to move oxygen around, takes a lot longer. Most experts say about three weeks to get to roughly 90 percent acclimatized, and up to six weeks to be basically fully adapted to wherever you are living. So a long weekend up high will teach you how your body handles it, but it will not give you fitness. A real altitude camp is measured in weeks, not days.

Pick one of two windows and stay out of the middle. If you can get there 5 to 10 days early, or better yet 2 to 4+ weeks early, do that. You clear the acute slump and start banking real adaptation. If you cannot stay that long, the next best thing is to show up as close to the gun as you can, ideally inside 24 hours, so you are racing before the worst symptoms kick in around day two or three. The window you want to avoid is roughly 2 to 5 days out. That one is the worst of both worlds, the acute symptoms are peaking and the helpful red-cell stuff has not shown up yet, so you feel awful with nothing to show for it. One coach reported a 48-minute improvement at the same race just by arriving about 66 hours out instead of 20 hours out. The timing alone is worth that much.

Live-high-train-low (LHTL) is the protocol with the best evidence behind it, and it goes back to Drs Ben Levine and Jim Stray-Gundersen. You sleep and spend most of your day up high, usually around 2,000 to 2,500 meters (about 6,500 to 8,200 feet), to kick off the red-cell and hemoglobin response. But you drop down lower for your hard sessions so you can actually hit real intensity that thin air would otherwise water down. The thing that matters is time, not the workout. The research points to roughly 12 to 14 or more hours a day of thin air for about three to four weeks to move your blood markers, and when it works it is often worth around a 1 percent gain. You get the blood benefit of living high without paying the tax of trying to train hard up there. And that is exactly why doing it backwards, living low and only training high, does not get you the same thing.

Below about 3,000 to 5,000 feet most runners feel basically nothing. Above that your effective VO2max drops by roughly 2 to 3 percent per 1,000 feet, and the pace you can hold at a given effort drops about the same amount, because pace follows oxygen. Put that into race times and you are looking at something like 3 to 6 percent slower at 5,000 feet, 6 to 10 percent at 7,500 feet, and 12 to 18 percent at 10,000 feet, with the high passes on a race like Hardrock going well past that. These are ranges, not promises. Your fitness, where you live, how acclimatized you are, and how much the climbs force you to walk all move the number. The honest answer is to plan a slower goal time up high and run the climbs by effort instead of expecting your sea-level splits to hold.

You lose water faster up high. The dry, thin air roughly doubles the water you breathe out compared to sea level, and you pee more while your body sorts itself out, so your daily fluid needs usually climb by about 10 to 15 percent over your sea-level targets, sometimes more. Keep your electrolytes going. A carb-and-sodium drink hydrates you better than plain water at altitude, and do not let your dulled thirst and appetite leave you quietly behind. The fueling leans toward carbs on purpose. Carbohydrate gives you more energy per unit of oxygen than fat does, so it is a more efficient fuel when oxygen is scarce, and altitude kills your appetite, which makes easy-to-stomach carbs and a rehearsed hourly plan even more important. Train your gut and your fluid plan during your block instead of winging it on race day, because the room for a stomach that quits is smaller up high.

Treat the mountain as the real opponent and altitude as a tax on top of that. First, build the climbing and the downhill legs the course is going to ask for, because trashed quads and weak power-hiking end more of these races than the thin air does. Second, plan your arrival around the curve. Either live high for two-plus weeks before the race (a common Leadville move is sleeping near 8,200 feet for several weeks while training closer to 5,000 feet), or, if you cannot do that, get in inside 24 hours instead of landing in the bad 2 to 5 day window. Third, go out easy. Keep your early effort low so your oxygen demand stays in check, walk the climbs you would run at home, and protect your stomach and hydration with a plan built for the elevation. A practice trip up the course a couple weeks out, plus a sauna or heat block at home, rounds it out for a sea-level runner.

Yes, and plenty of strong mountain-ultra finishers come from sea level. You cannot fully replicate altitude at home, but you can stack the levers that matter: train your vert and downhill legs hard, since the course usually limits you more than the air does; consider sleeping in an altitude tent at roughly 12 to 14+ hours a day for three to four weeks if you want a genuine blood response; run a heat or sauna protocol, whose plasma-volume benefits partially overlap with altitude adaptation; and rehearse a higher-fluid, carbohydrate-forward fueling plan. Then time your travel intelligently, arriving either well in advance or inside 24 hours, and commit to pacing the race by effort rather than by your sea-level splits. The single biggest sea-level mistake is not the lack of an altitude tent, it is running the early climbs at home pace and blowing up.