Ed Viesturs the first American to reach the 14 highest peaks in the world without supplemental oxygen has more lung capacity than the average person. The more lung capacity you have the better you’ll perform at high altitude. Although a big part of lung capacity is biological it is possible to increase your lung capacity through proper training. I think swimming is a great way for mountaineers to increase their lung capacity.
There are a few tips to get the most out of your swim workouts when preparing for altitude;
1. I find that the crawl stroke works best since you forced to control your inhale and exhale to certain times. Aim for inhaling every 3 strokes as you turn your head to the side and exhaling in the water.
2. Try and exhale completely a second or two before inhaling. If you feel you have to inhale more often than every 3 strokes slow down, if you feel you can breath too easily speed up or decrease your inhale to every 4 strokes.
3. Your swim should be at 17-18 on the Borg Exertion scale
. It’s ok to do 50 or 100 meters, rest for 60 seconds, and then do another sprint.
4. Aim for at least 1000 meters of total swimming or 30 minutes once you have a good base.
5. Another workout you can do in the pool is to swim underwater. This is something that was introduced to me in the Air Force Pararescue program. Only the fittest athletes who have consulted a physician should try this with a lifeguard watching. It’s not uncommon for swimmers who push themselves too far to pass out underwater, so start off slow and easy. Try and swim an entire length of an Olympic sized pool under water (25 meters) then crawl stroke back. Wait 45 seconds then do the next underwater. Aim for 6-10 maintaining the 45 second rest between underwater. When underwater you can use a modified breast stroke then glide till you stop before the next stroke. Blow out your air slowly.
Here's a video showing the underwater swim technique
Swimming is also a great way for mountaineers to get in shape during the off season or for those looking to recover from certain injuries with a low impact activity. This article assumes a base level of swim fitness and good swim technique. If you don’t have good swim technique it’s easy to take an adult swim course through your local YMCA or Park District.