I started having knee problems when I hit the 50+ mark (age, that is)
so had a lot of knee pain when I began riding. I used a knee brace the
first year, but finally discovered that most of my knee problems
were/are due to my equitation. Whenever my knees began hurting, I stop
and check my balance; I usually find that I've gotten stiff and am not
flexing, so I start consciously relaxing from the toes up. It works
wonders for me, but the problem with your knees may be different than
with mine. Good luck as I know gritting your teeth and popping aspirin
while going down the trail is not much fun. Patricia