First thing: I know this is caused by over training so don't bother telling me that. Background: I've been training again for about a month and have wanted to introduce swimming into my training for years. Two days ago I did an intense sprint session (2.5 miles) so I decided to make yesterday my first swim day. After flopping around in the pool for about 150-200 meters both my calves locked up on me and there was no way I could continue. Today I can barely move due to the pain in my left calve. Situation: I was hoping to swim 500-1500 meters on days when I need more time to recover before running. The swim technique I'm trying to use is freestyle. I thought swimming would be hard on the arms and thighs... calves never really crossed my mind but I don't know how to swim so that doesn't surprise me. Is this swimming a bad choice for recovery from running? Should I try to use a different swim technique?