I've been off the bike for 3 weeks now with swelling and pain behind the knees, which I blamed on getting fitter and stronger, going out looking for hills and then mashing my knees. Both my GP and a cycling physio have checked my knees and my bike position and can't find any definite reason for the problem. However on Saturday I had a sudden insight into the problem; I usually go swimming on Saturday mornings with my young son and I am an unskilled but enthusiastic breaststroker; my swimming is usually in vigorous bursts rather than prolonged. We haven't been for three or four weeks and last Saturday I had a sudden flash of insight when I began to swim and experienced quite a lot of knee pain. I also realised that in the pool we have recently been playing a new game with the floats that involves me backing up to the side and pushing my son off hard on a float by straightening my legs, which are usually bent out awkwardly sideways rather than folded beneath me. This does create momentary pain in the knee joint. I have Googled knee pain in breaststrokers and have found a lot about joint and ligament damage caused by poor technique putting lateral strain on the joint. Thinking about it I realise that the swelling and slight pain behind the knees had already started before I went looking for steep climbs (I did a 12% hill, mostly standing on the pedals) so I am wondering if the hill climbing is a red herring and the damage was actually caused in the swimming pool? Any swimmers on here with experience of knee pain from breaststroking?