Pole height , with your arms at a right angle bend at the elbow, that is, upper arm vertical down by your side to your waist, fore arm horizontal, the grip should fit neatly in your hand. On normal trails it will be mostly your forearm that flexes , a whole arm sweep from shoulder height is more the sort of action adopted by people in very active xc skiing where you get a push from that position right back behind you, even to the extent of partly releasing your grip,just thumb and two finger tips, pressure being from the side of your palm on to the strap not from your grasp of the grip . Knee pain, answer, lot of leg extensions on a gym machine.And while you are there, lots of tricep exercises to give you more power with your fore arm movement.