For me it's a leg problem that appeared since I joined a running group last month.
As an cyclist I wasn't physically prepared to run fast intervals right away.
I'm visiting my physio tomorrow to have the knee and leg checked. I'll probably have to take time off and passively watch the first snow flakes come down ... :-(
I was surprised to "like" the few back strokes I did yesterday. I will definitely add it to my sessions in the future.

Louis :-)