Preparations.

I am used to long walks, so the 20 day trek doesn’t seem very formidable – having a porter to carry everything except what I need during the day (water, rain gear, a couple of granola bars) will make it seem almost luxurious. But the trek will take me over Thorong La, a pass just shy of 18000 feet, a full mile higher than I have ever been, so a bit of extra advance conditioning seems like a good idea. My usual workout, 3-5 days a week, is a combination of situps, pushups, stretches, and 35 minutes of climbing the basement stairs carrying 75 pounds of sand strapped on a beat up old pack frame. That would probably be enough cardio-vascular fitness preparation, but I saw an article about research on physical fitness in a recent issue of New Scientist (Jan. 6 2010) that included a section on oxygen consumption capacity (VO-Max), and some interesting additions to my routine, so I decided to give it a try. The exercises are written for running, but it was easy to adapt them for a stationary bike. The basic pattern: maximum effort for 3, 4, or 5 minutes, and work out average speed. After a rest period equal to the length of the initial run, cover the same distance at 80, 85, 90, or 95% of the initial average speed, rest 45-90 seconds and repeat several times. Be sure pulse rate drops to 120 or less during each rest period – lengthen the rest period if necessary. According to the author, if you do this 2 or 3 times a week for a month it will increase VO-Max. I've done it for over 3 weeks now and can't detect a difference, but I feel good after finishing it so I will probably keep it as part of my routine.

5 min. at max speed; 5 min. rest; 6 min. at 80%, 30 seconds rest
4 min. at max speed; 4 min. rest; 4.5 min. at 85%; 45 seconds rest
3 min. at max speed; 3 min. rest; 3.2 min. at 90%; 60 seconds rest
5 min. at max speed; 5 min. rest.; 5.25 min. at 95%; 90 seconds rest
3 min. at max speed; 3 min. rest.; 3 min. 9 sec at 95%; 60 seconds rest

You can measure your VO-Max with a walking test described here: Rockport Fitness walking test. See the New Scientist article for other details and links to other tests.