basically his(the guy who hikes) bones, especially in his legs, would get stronger. wolff's law states that a bone will adapt to the forces/loads placed upon it. the bones gets thicker, particularly the external cortical layer. conversely, someone who does not exercise at all would have weaker(more brittle) bones due to the lack of forces put on his bones, they become adaptively thinner. as matter of fact, bed-ridden people tend to develop osteoporosis