I get cramp in the evening, after a hard day's work. It is always hot weather, so I've been sweating, and I've just blobbed out after working hard.
If I drink plenty of water DURING THE DAY, I don't get cramp. If I keep moving about in the evening, I don't get it either.

Vibro massage and salty water fixes it eventually.

Oddly enough, I get it in the thighs, but my upper body usually gets the harder workout.