Nop200 wrote:
Just keep in mind that unless you're on a treadmill, what goes up must come down. Downhill running can be extremely risky, as it puts a huge amount of stress on your body. (I'm talking about 1000ft+ in a single run) Hurts your quads and knees especially.
Going really fast safely at running downhills is trainable. I'm older (46), but I like to fly downhills. On a recent run on something I often train on, I went 5.4 miles and 2200 ft up (with 40 ft down near the beginning, average about 7 percent grade) at 8:51 pace, then turned around and did the 5.4 miles and 2200 ft down (and 40 ft up) at 5:07 pace. On the downhill, I covered 1K in 2:53, 1 mile in 4:49, 5 miles in 25:20, before that final 40 ft uphill slowed the overall pace to 5:07. My quads were 100% like normal at the bottom, and my knees also 100% fine. With good form, the stress is absorbed by the muscles, not the joints. And apparently not too much with the quads when you are going that fast. I don't have a pounding sensation when running fast downhill. When I do feel like I'm pounding on a downhill, it's because my weight it too far back and I'm braking more than trying to go fast.
In the local XC series, I have much better downhill speed compared to the other guys around me with slightly better uphill fitness. I am often blowing by people at sub-4 pace according to my GPS (saw 3:45 pace last week). My average training pace, due to the elevation gain and trails I run on is only 10 to 11 minute pace on average, so you don't necessarily lose speed with tons of climbing/descending if you also go fast on some of the downhills.