Yesterday I did a series of downhill repetitions with one of my athletes in the Pentlands. To me this is an element of trail and hill running that is too often ignored. The approach is more likely that when in races (especially longer ones) to take the descents easy so as not to trash the quads. Runners more commonly train for the up and not the down.
I myself learnt this the hard way in my first attempt at the Pentland Skyline race in 2010 where after a very strong first half the lack of downhill running made my legs cramp up dramatically in the 2nd half.
Anyone planning on running the Pentland Skyline or any other race which has a significant amount of descending this year should spend a fair bit of time running fast and hard downhill. The principle is the same as with uphill reps. These are not easy sessions and your quads will hurt from them but come race day you will reap the rewards from this. Caroline McKay did these in her build up to the Western States 100 mile ultra which she finished in less than 24 hours inside the top 20 of all female runners.