Just a possibility:

Thanks to Hitchy, I've recently become aware of an unusual syndrome
in which the external iliac arteries can be temporarily "squished" or kinked
when cycling. This is more common amongst cyclists than other sports people.

The external iliacs become the femoral arteries which mainly supply the muscles
on the inside of the legs.

If blood supply is temporarily impeded, temporary claudication can occur, which often presents as a vague, "cramping" sensation.


JUST A SUGGESTION