I would look into bike fit issues, as well as posture on the bike.

A long while back, I was getting numbness in my toes that came from having my seat too high. I have a recurrent problem with numbness in my pinky finger, which occurs when I slouch too much at the computer--it is a mix of bad posture at the neck shoulder area and too much time using a mouse.

Alternative interpretation: I get a tingling sensation in my calves on the first major effort of a ride, whether it is a sprint or a hefty climb. This seems to be from an expansion in the blood vessels. I don't worry about this, since it is a light sensation (at or near the skin) and lasts only a minute or so.

You could test if this is the case by going for a ride where you go gently for a good 20-30 minutes, then sprint like the devil for a minute or two. Does it occur then?

Good luck!