[acadien]

Do you (or anybody) have evidence to support this? Genuinely curious since everything I've read shows that surface doesn't matter. I understand this result is counter-intuitive but I was under the impression its a well documented result.

[chatmasta]

Nothing beyond personal experience and knowing my own body. After you run every day for 8 years of your life you tend to notice little differences in how you feel day-to-day. For example, it's not a coincidence that after three months in Houston running on only pavement, I had far more ankle/knee/plantar pains than after a season of running on trails. Also, trails have the added benefit of activating a greater diversity of muscles in your feet, because you need to "dance around the roots."