The anatomy of speed. Researchers used MRI to look deeper at Asafa Powell, one of the fastest men in history. They found His psoas major was nearly twice the size of another elite sprinter’s. That muscle drives hip flexion and leg recovery, helping reposition the thigh quickly at top speed. Next, they analyzed his tendons. It took 114 kg of force just to stretch Powell’s tendon by 1 cm, more than double another elite sprinter. That kind of stiffness lets him generate huge rebound forces in minim