I got one for you. Not all the time, but once in a while, when I am "off" I can concentrate really hard on a big step forward...and break out into a SPRINT!!! I can keep going as much as 1/2 a city block, maybe 20-30 seconds (?). When I stop running I slow down and within seconds (2-3) I am back to my "off" condition.

Try to explain THAT with a "lack of dopamine" theory.
Keith