I go climbing (theoretically) once a week. The theoretical part is because at the moment I keep coming up with excuses as bad as the ones I used at school to avoid PE. I'm not sure why I'm avoiding it. I actually like climbing. Admittedly I am rubbish at it. The visions I had of astounding people with my natural ability when I first decided to try it have not exactly been evidenced. I am a natural optimist. Kind of. I always hope to be brilliant at any new sport I try. Sadly climbing, is not something at which I naturally excel.
However I will continue to go to climbing, struggle my way up the walls (Spiderwoman I am not) and come back down replete with bruises, scuffed elbows and knees and grazes. Not to mention pulled muscles. So far I have never come back from climbing without bruises round my knees. My climbing partners don't understand this. Knees are not involved in climbing - except as the useful bending joint which enable you to go up in the world. Why mine end up the way they do is a complete mystery. I think I will worry less about the little purple circles and more about whether my knots are tight.
After all, when you are tied to a rope and all your weight is balanced on two little footholds, knots not knees are your priority.