Couple of trail-running links I found on the Team Oregon website. As a relative newbie to this type of running, I found them interesting. (Long-time trailrunners may perhaps find them mundane):
(Dragged my bad right calf out onto the dirt trail today and managed about 5-1/2 miles at nearly 9:00 pace, a major improvement to my injury status, and I am feeling very encouraged. The soft dirt seems to be a plus for injured runners, though as these articles point out, YOU MUST STAY FOCUSED on your landings/footings).