Subliminal psychic vibration of one's molecules, allowing hyperacceleration of normally-slower movements.
Psychic fortification of muscles and hyperstimulation of motor nerves, allowing them to act and react faster than normal.
Psychic acceleration of time around the brain, heart and lungs, allowing accelerated thoughts, reflexes and motion, with no harm to the circulatory system (as the acceleration comes from speed-up of time, not the overexertion of the body)
Gotta think of something harder than that.
“…Judge not what a man has done, but judge what he could have done if he was a different bloke altogether. For art thou a leper? And a leper can changeth his spots…” --Rudy Wade, Misfits (Series 4, Episode 8)