I live in a very hilly area and most of my running is done on dirt roads. There are few routes that I can do which will not end up doing a fair amount of up and downhill running. I have not really been doing much speedwork yet as I have mostly focused on building my endurance over the past year or so. I do have occasional access to a local HS track so I can do some workouts there. My question is whether there is a benefit to also doing some speedwork on downhills? Will it "teach" my legs to go faster than usual or what I am maybe capable at on the flat at this point? Is there an increased risk of injury which will offset any benefit to the work? (Most of the hills are on nicely maintained dirt roads) How steep of a drop becomes too steep to bother with? Should this be for longer intervals or shorter? Etc. Any thoughts?