Pay attention to the pain...
A blister might seem bad, but I don't see how its going to kick you off the trail permently.
Much worse are the stress fractures and metatarsalgia (which basicly means pain in the ball of the foot). The metatarsalgia is what kicked us off.
To prevent stress fractures, don't do big miles until you've conditioned your body well. I would say you need at least a month before you start doing big miles (over 17). You might feel able, and a lot of people probably do that, but you are taking a chance because you muscles are developed to 20 mile days. The tired muscles let the bones take the beating, leading to stress fractures. Of course a month may not even be enough. From marathon training, it takes 18 weeks to go from nothing to ready to run 24 miles. But that's only training 5 days a week.
The metatarsalgia (often described as the ball of your foot feeling bruised) is much more difficult to figure out. It can be caused by several things, including neuroma's (Morton's Neuroma is a common one).
A neuroma is a nerve between your toes (the most common one to be a problem is the one between the 3rd and 4th toes, 1 being the big toe. It can happen between the 2nd and 3rd too) that is aggravated each time you take a step. Eventually it becomes inflammed, and can become perminently painful. It can be fixed by orthotics if you are lucky, or surgery if you aren't. Another option is getting Cortisone shots on trail to let you keep hiking. We think this is what happened to my wife in 2001. We are finally (!) getting around to getting to the foot doctor to see if he can truely diagnose it.
Other things that can cause metatarsalgia is shoes that fit too tight in the toe box, bad foot structure or bad cushioning. Or all three. It's tough to say why some people will never have a problem, but I think most people feel that bruised feeling in the ball of the foot at some point. Most likely due to the nerves getting pounded.
There are a few things that we are going to do to make sure we don't get knocked off trail again.
1) Get the current problem diagnosed and fixed, whatever that takes. We will do long section hikes to make sure that it is really fixed.
2) Take breaks when the feet start to feel bad. Normal aches and pains when you start is par for the course, but pain that won't go away or that gets worse demands that you take a zero, or two, or even a week.
3)Increase the milage slowly
4)Get trail shoes with air soles in the front and back.
5) Make sure there is plenty of room in the toe box
6) Custom orthotics for both of us (NOT CUSTOM SUPERFEET! These are not made to give you the support that a proffesional will build in. They only match your foot shape. We had these and they were worthless for this problem.)
7) See a foot doctor if we get a problem. We might even (GULP!) fly back home to see the one that we are getting ready to see. There's a big difference in quality of docs when it comes to something as unique as long distance hiking. It's expensive, but it could keep us on trail.
8) If all else fails, cortisone shots and Vitamine I. In fact, we plan on taking Ibuprofen to try to manage the inflammation from the very beginning.
So that's about all we can think to do. Man, I can't tell you how much it stunk to get knocked off trail, but we will do everything we can to stop it from happening this time.
Gravity Man
PS Another common problem is achilles heel (streach those calves) and ache support. I strongly recommend seeing a highly acclaimed foot doc before hitting the trail. He will get you set up with orthotics to compensate for any structural problems with your feet. An ounce of prevention...