One time, I was trading Facebook messages with an acquaintance who was asking me about my through-hiking experience. I think he asked my opinion about the best way to prepare, and it seemed to surprise him when my main recommendation was to join his wife in going to gentle yoga classes. He wanted to know why yoga would be helpful for hiking in particular. I wasn't sure how to answer that, and it was at least a year later when I finally wrote back and explained my suggestion. This is what I told him.
Yoga, in itself, is not magic, and it is not the "only" way to go. But, it is a great tool for increasing your bodily awareness. Connection between mind and body might be the single most important factor in being a successful human being -- "successful" defined as happy, healthy, and confident, not necessarily as completing your life exactly as planned. This applies to the journey of thru-hiking as well. So I recommended yoga, and would still recommend it, but I also think that a 10-day Vipassana meditation course would be an excellent way to prepare for a thru-hike, or perhaps a martial art, Feldenkrais classes, dancing, or really anything that draws your awareness into different areas of your body and helps you find acceptance there.
When we are not aware of our bodies, we miss out on some very important information. To a large extent, we store our subconscious emotions in various parts of our bodies, and we have tendencies of aversion and craving toward these sensations that result in patterns of tension, constriction, restlessness, or any variety of things. If we want to navigate life in a truly skillful way, we need a direct connection of mind and body, so that we are aware of our deepest intuition and wisdom when we are presented with decisions. A wise thru hiker is always aware of their bodily and emotional needs, and does not hesitate to deviate from the "expected" action in order to meet the needs that are so particular to the individual.
If this reasoning seems too metaphysical for you, consider it this way: you are going to take millions of steps between Mexico and Canada, using your body for every one of those steps. You want to know how to use your body efficiently, to conserve energy, and also to protect your joints from wear and tear due to improper use. To do this, you will need to have an adequate range of motion in your joints so that you can perform these motions in the way that is most mechanically sound. Say, for example, the muscles and fascia in your quads and hamstrings are habitually contracted, as they are for most men in our society. This will the limit the ability of the strong muscles in your hips and pelvis to do their job, and you will have to compensate with the use of other stabilizing muscles like your calves, leading to fatigue and overuse injuries. Furthermore your pelvis will likely have an anterior tilt, creating tension and pain in your low back. Using a practice like yoga or meditation, you can re-pattern your experience to relax those tense areas and experience more ease, balance, and agility in your movements, leading to a healthier body and ultimately a more balanced mind.
Hiking itself can prepare you for hiking, to a certain extent, but a preparation involving hard work and repetition is incomplete without developing careful attention to sensations throughout the body. We exist in our entire bodies -- not just inside our heads.
