Marvel: Speed Physiology

Jacqueline Falsworth (Spitfire)
Spitfire's entire body is oriented toward the rigors of high-speed running. Her cardiovascular and respiratory systems are more efficient than a normal woman's. She metabolizes an estimated 50% of the caloric energy content of foodstuffs. The chemical processes of Spitfire's body are so highly enhanced that her body does not generate fatigue poisons, the normal by-products of locomotion which force the body to rest, as quickly as a normal human being does. Her tendons and bones have somehow become stronger in order to withstand the stresses of high-speed motion, and her joints are smoother and lubricate more efficiently than a normal woman's. Spitfire's heightened metabolism afforded her great resilience to impact-related injuries. Her reaction time was about twice as fast as that of a normal woman.

Pietro Maximoff (Quicksilver)
Quicksilver's body is adapted towards the rigors of high-speed running. His cardiovascular and respiratory systems are many times more efficient than those of a normal human being. He metabolizes an estimated 95% of the caloric energy content of foodstuffs. The chemical processes of Quicksilver's musculature are so highly enhanced that his body does no generate fatigue poisons, the normal by-products of locomotion, which force the body to rest. Rather, this body constantly expels waste products during his accelerated respiration through exhalation. His joints are smoother and lubricated more efficiently than those of a normal human being. His tendons have the tensile strength of spring steel. His bones contain unknown materials significantly more durable than calcium to withstand the dynamic shocks of his feet touching the ground at speeds a human could never achieve or withstand. Quicksilver's practical reaction time is several times faster than a normal human's and the speed at which his brain processes information is heightened to a level commensurate with his bodily speed, enabling him to perceive his surroundings while traveling at high velocities. Quicksilver's tachrymose is more viscous than normal, thus preventing rapid evaporation and replenishment of surface fluids on his eyeballs under the influence of high wind velocity to occlude his vision.