Technique is just as important as being in shape. If you are exhausted, you may be wasting energy. Read about and perfect the rest step, rythmic breathing and proper use of trekking poles. Also learn to properly shift your weight with each step. Shift weight over the forward foot and stand up - do not put the foot forward and pull your center of gravity forward. Avoid a lot of side-top-side wobbling. Step over obstacles instead on top of them. Try to place your foot horizontal on small features. Start slowly and gradually and steadily work up speed. Avoid stop and go - be like the turtle. Take a short (5-minute) rest stop every hour. Eat munchies at each stop, drink water.

As for staying in shape, I live near sea level in a fairly flat place. I walk from my house to the river (a 6-mile route) about 3 times a week. I bicycle about 20 miles twice a week. I try to do a 2-3 day trip a couple of days a month. And, I eat right and keep my weight down. I have found that the stair-master works best for me as far as gym routines. I do not run anymore because of old knees. I wish I liked swimming because for us old folks, this is supposed to be the best exercise. Still cannot do it - I hate to be in the water.

Good luck on your trip. Have fun.