777 wrote:
Well I'd have to disagree about trails. I've had injuries that were severely irritated on pavement but were almost normal on trails. Bounce a golf ball on asphalt and dirt for an illustration of why trails are far superior. Road running also carries the risk of being hit by a car, let's not forget that.
What does bouncing a golf ball off the asphalt have to do with anything? It just proves that energy on a hard surface is given right back. You are making the fallacious assumption that hard surfaces, and by extension impact, is inherently a bad thing. Impact is a function of three variables and one constant (gravity): 1) body mass, 2) velocity, and 3) instantaneous deceleration at foot-strike. I'm pretty sure that the foot-strike gives the least impact on the final impact calculations. Somewhere in a thread here someone published a study on injury rates over the last 30 years. The shoes became noticeably soft, yet the injury rate hadn't changed one bit.
I've had one stress fracture in my life, at a time when 50% of all of my running was on soft surfaces, dirt trails or grass. In fact, the day that my foot cracked, I was just finishing a 10 mile run, all of it on trails or grass. During most of my career, I'd estimate that 95% (or more) of my training was on asphalt or concrete. Never had another stress fracture again.
On those same soft trails I did trip over a root the week of NCAA XC (I was undefeated and set the course record everywhere I ran up to that point) rolled over with my arm caught behind me and dislocated my shoulder. It was not a pretty sight. As you can see, I gave two specific real-life examples to the risks of trail running.