What Altitude Does to a Fit Body (and How to Prepare)

I have trekked above 14,000 feet on four continents. The Annapurna Circuit in Nepal. The Lares Trail to Machu Picchu. Mount Toubkal in Morocco. Kilimanjaro. And the thing I keep relearning is that altitude does not care how many miles you logged last month.

After 50, this gets sharper. The Wilderness Medical Society published guidelines showing that cardiovascular response to low-oxygen conditions slows with age. Your heart and lungs still adapt. They just take longer to get there. So the margin for error shrinks, and the cost of impatience goes up.

But here is the thing worth holding onto: the Tetons, the Wind Rivers, the Colorado 14ers, the Haute Route from Chamonix to Zermatt, all of it is accessible to fit people over 50 who give their bodies time.

The sleep-low rule (and why people break it)

Above 8,000 feet (2,400 meters), do not increase your sleeping altitude by more than 1,000 feet (300 meters) per day. For every 3,000 feet of gain, take an extra rest day. This guideline has not changed in decades because the physiology has not changed.

I know why people ignore it. You flew across the country, you have five days of vacation, and you want to be on the trail. So you land in Jackson Hole (6,237 feet) and hike into the high Tetons the next morning. By noon you have a splitting headache and you are moving at half speed. I have done this. It is a bad plan every time.

Two nights at valley elevation first. Day-hike higher. Sleep low. It feels like wasting a day. It is buying three good days instead.

Your fitness will not protect you

This is the part that trips up strong hikers. A fit 55-year-old with a resting heart rate of 52 and a 200-mile month is not protected from acute mountain sickness. AMS is about ascent rate, not aerobic capacity. I have watched ultrarunners get nauseous at 12,000 feet while their less-fit partners felt fine.

What fitness does buy you: the ability to manage effort over long days, to recover overnight instead of accumulating fatigue, and to keep moving when the trail gets steep and the air gets thin. On a five-day traverse in the Winds or a hut-to-hut crossing in the Dolomites, that difference between recovery and accumulation is everything.

Diamox: skip the pamphlet, here is what matters

Acetazolamide (brand name Diamox) is the drug most trekking doctors prescribe for altitude. It works by making your blood slightly more acidic, which tricks your body into breathing deeper and faster. You acclimatize quicker. Simple as that.

I have taken it above 4,000 meters in Nepal and above Thorong La pass at 5,416 meters. The side effects are real but manageable: your fingers and toes tingle, carbonated drinks taste flat (genuinely annoying), and you will pee constantly. A sports medicine doctor or travel medicine clinic can prescribe it and tell you whether it makes sense given your history, especially if you take blood pressure medication or have kidney concerns.

Ibuprofen helps with headache symptoms but does not speed acclimatization. It is a band-aid, not a fix. And the only real fix when symptoms get worse is to go down. Altitude is the one opponent you cannot push through.

Training for thin air when you live at 600 feet

Build the biggest aerobic engine you can. Long Zone 2 sessions, the kind where you can hold a conversation but would rather not. Three to four per week in the months before your trip. Your body cannot pre-acclimatize at sea level, but it can arrive with enough cardiovascular headroom to handle the reduced oxygen without falling apart on day two.

And then there are legs. Leg strength matters more than most people expect, and more than most training plans prescribe. Loaded squats, weighted step-ups, Bulgarian split squats, heavy single-leg work. The mountains do not care about your bench press. They care whether your quads can handle 2,000 feet of descent with a 30-pound pack after eight hours of hiking. Train for that or discover the gap on the trail.