Hardly scientific, but my own experience on a 200 with only three hours sleep, supports this.
The last fifty were particularly lumpy and when I got out of the saddle, the tops of my thighs were fluttering with "pre-cramp": I guess if I had stopped pedalling I would have seized-up there and then.
http://regressing.deadspin.com/everything-you-know-about-cramps-is-wrong-and-gatorade-1587102837