PM 8.2 with one of the hardest workouts of my life. 1 x 1k from 7100->7250 feet (554 pace)
then 3 x 800 meters up the same hill averaging just under 6 min/mile pace I think.
Seriously thought I was going to die. Awesome pain though. The type of stuff I need in order to be stronger late in races.
In terms of preventative measures for stress fractures, and general injury prevention
a) running on soft surfaces/trails as much as possible. I usually save the asphalt for workouts. Unstable soft surfaces are easier on your body, and the uneven surface forces your body to develop strength in the smaller support muscles in your legs, so that when you run you are better equipped to brace against the impacts that can cause stress fractures
b) practice running barefoot. Strong feet and legs make healthy runners, and running 10+ miles a week on grass with no shoes is a great way to develop both proper running form and additional strength in your feet.
c) do form drills - proper running form leads to less impact on your bones, and a more efficient stride. You will be less likely to injure yourself if you can consistently run with good form. This helps a ton in getting faster as well. Take a look at this link to see one of the US Olympians, Dathan Ritzenhein demonstrating form drills. He is a guy who was once plagued by injuries (especially stress fractures), but with new coaching and a new routine he has been running injury free for a while.
d) Run with proper footwear. Go to a running shoe specialty store if possible (or you can use runningwarehouse.com's online form analysis) and get fitted for the right type of shoe. This will help to protect your feet and ankles from absorbing the wrong type of shock.
e) LISTEN TO YOUR BODY - do not try to run through injury. Take a couple rest days if you are hurting, and then start back up slowly. If symptoms do not go away, get to a doctor to get yourself checked out.
f) Do hill repeats. These make you a beast, and beasts are less likely to get hurt!
g) get enough to eat. Make sure you are getting calcium and protein in your diet, as well as salt and carbs so that you have enough fuel to rebuild muscles and recover. Also staying hydrated is super important.
Sorry for the lengthy response - just my 2 cents on some ways to stay running healthily.
Here is a pic of me getting my ass kicked at that last xc meet. Obviously my form has broken down a bit . . . .
I did beat the old guy by about 20 seconds or so - he is one of the best masters runners in the country though, and I lost to his brother . . .