hobkirk, aren't you getting back into cycling after injury?

The thing is, the quad in the area that cramped plays a fairly significant role in pedalling. And if that muscle hasn't been exercised for a while, to the same level as you did on the ride and walking, it is going to protest.

Take solace in that, I think, this is a passing phase.

Management of rehydration and electrolytes as you ride (and walk) will help, but mainly, getting out there and riding and getting that muscle used to working again is the main thing.

(I get these from time to time coming back to riding after a lay-off, or during very long rides, either touring or doing randonnees. There's nothing like crawling into a tent and have a quad muscle cramp... because as you observe, there is almost no way to overcome it.

I've even had the muscles in both legs fire off at once, and I can tell you, that was absolute agony that left me feeling sick in the stomach.)