The Mechanics of Running Hills
Running on level ground requires somewhat different mechanics than going up and down hills. What benefits a long-distance runner on flat ground can fail you in negotiating hills successfully. One of the few good things about hills is that they force you to use muscles you don't normally use, and, if you're fortunate, you get to run as many downhills as uphills.
Even though you won't be able to maintain the same speed running uphill as you do on the flats, try to maintain the same effort level. Exaggerate your armswing to assist your legs. Imagine that you are cranking your way up or pulling yourself up the hill using your upper body. Shorten your stride, lift your knees higher, lean slightly into the hill, and power on up.
One of the best things about running downhill is that you can use gravity to your advantage. It is a valuable running skill to learn how to negotiate a downhill effectively without losing control or wasting energy by holding back your speed too much.
Although your natural tendency is to lean back when going downhill, you should instead lean forward slightly to maintain a posture in relation to the ground, as if you were running on the flat. Try to keep your footstrike light so as not to grind your heels into the hill as a braking mechanism. Use upper body positioning (leaning) to make speed and body balance adjustments relative to how steep a grade you are running down.
Runners with little prior experience with downhill running should be careful. The biggest risk of injury is to your knees and quads. By catching your “controlled fall,” your quadriceps do the bulk of the work of braking. On long downhill stretches, your quads can be overworked without your being aware of it.
If you are racing in a short race, you may lean forward a bit and fly down the hill, but certainly be more careful in training. In fact, many runners who use hills as part of their advanced training either walk or lightly jog down a hill to recover before charging up again. This is a good way to rest and recover while avoiding the excessive knee stress that downhill running can cause.