From my experiences my feet and those of fellow riders who have had
hot foot, is that it results from lack of circulation, something that
affects over 40 riders more than youthful ones. Although it seems to
strike randomly, I find it occurs mainly while pedaling without letup
(slight grade) where pressure is constantly on the ball of the foot
preventing circulation.

I deduce this from the cure I have used, and that its to intentionally
pull up on the pedals on the up-stroke to get air under the feet.
This has worked well and I am still using the Shimano SPD shoes I've
had for years.

SH-TO92 a shoe that seem to have been replaced by an new model under
the shoe heading "Road, Sport, and Touring Shoes".

http://tinyurl.com/3r6g59

A similar ill comes from braking continuously in cool weather so that
the fingertips beyond the lever pressure point become pale and seem to
freeze. This effect can be observed by hooking left and right index
fingers together and pulling. As the fingertips turn yellow,
circulation ceases.

Jobst Brandt