On my humid run today, I was thinking about how silly I may look hustling up one of my mammoth sized hills and walking down the hill. However, there is a secret to hills which would be walk down them in practice so you do not put too much stress on your knees. There was a time when my coach taught me how to race going on the downhill, then evolved a period of training where downhills are for special practices and actual races. I recommend saving your knees and walking or slowing down for downhills on the regular, because knees are like brake-pads, as cartilage never grows back. All those times you save them in practice pay off during a race. Nevertheless, there is a form and technique to racing down hills everyone needs to acquire, running up hills is the more important thing in training for me.