It's the heat. Are you taking in enough salt? Both my calf muscles nearly went into cramp on consecutive nights, I've been running in the heat and probably not taking in enough salt, so I increased my intake, been all right since.
Increased my run to 5 miles this morning, so I'd better make sure I have some extra salt.
Running
I probably don't drink enough. I don't think salt is the issue, I'd put salt on salt pie, me.
Thank you all for your sympathy
This is what happens if you're old, don't do some form of moderate exercise and eat lots of cake.
But cake is really nice
Let them eat cake and run.