My lung capacity sucks. I haven't found a way to fix it either (so if you do, let me know!) Yoga has helped a bit. Though I'm not in the best athletic shape either...

My two cents (I learned this from WD) - just go your own pace. I go faster by going slower! (breaks are shorter and less often) And as much as I love my husband, he can go suck eggs on the whole hurry up thing You will be happier if you go your own speed or the speed of the slowest person in your group. If someone is slower than you, just take that time to take pictures or enjoy the view.