Running and heart rate?

I love running, and cardio workouts are a great way for one to increase overall fitness. What exctly should i avoid when i ramp up my intensity during a run? What are the ways in which my run workouts could result in injury? According to an article, walking as primary form of cardiovascular workouts resulted in fewer injuries. One study looked at 5,000 men and women all aged under 45 from 1987-1995. The study compared the amount of injuries found among them, and utlimately resulted in a significantly higher amount of injuries in those participants that were runners. in the study, nearly 700 of the runners admitted suffering some sort of injury that required doctor attention, while only 160 participants that walked admitted to similar injuries that required doctor attention. My main take away from the article was that running is higher impact, and results in greater risk of injury.
Colbert, Lisa. "Physical Activity-Related Injuries in Walkers and Runners in the Aerobics Center Longitudinal Study." . 02 OCT 2000, n.d. Web. 11 Mar 2012.

What about stretching after a workout? How affective is stretching at preventing injury? One article helped answer that question. The article included a study in which Range of Motion (ROM) was tested to look at how much if any ROM improvement was noticed as subjects stretched following a workout. The study looked at reducing muscle stiffness and fatigue after workouts. The study concluded that no sign of tension inside the muscles could be found following short term stretching. In non scientific terms this means that subjects that stretched following a workout did not report any change in tightness or soreness while using stretching. Basically they felt the same after stretching as they had before they even finished their workout. I guess what this means to me is that stretching is one of those things we're always told to do by out coaches and teachers growing up, and this article confirms a suspicion of mine that stretching is important for you, but not that important for you. You can get by without it.
Wiemann, Klaus. "Influences of strength-, stretching- and circulatory exercises on flexibility." . 18JUL1997, n.d. Web. 11 Mar 2012