I've seen several posts recently (here and in CR) discussing the importance of optimizing downhill periods during heart rate training base-building sessions. I agree that this is a good idea and want to make sure I incorporate this concept correctly into my runs. On the other hand - I am sensitive about running too quickly on the downhill sections -- as -- after learning the hard way -- I have been taking it fairly easy on the downhills recently in order to minimize chance of injury. In short -- I am curious as to what sort of downhill slope is optimal for balancing the benefits of HR training without incurring additional risk of injury? I suspect that there is a fair degree of variation on this - depending on a host of variables specific to each person - but anyway I was wondering if anyone has experimented with this to find the best combination of distance/slope?

A few rules of thumb:

1. build up a downhill running addition *very* gradually - don't jump right into 5 miles of downhill runs. Also work your way up to higher inclinations slowly as well.

2. Use very short strides with fast turnover - don't just let yourself go so that you get a good pounding.

3. Don't brake while going down.

4. lean forward just slightly when going downhill.

Most importantly, try to move smoothly with gravity - don't just "fall." Give yourself a good 8 weeks or so before working up to any significant (say 5-10 miles a week) of downhills. Your quads will take a bit of a beating at first, but once you get a rhythm down, that will subside.