World champion sprinter Usain Bolt may have an asymmetrical running gait, say researchers, throwing into question whether symmetry matters for speed. Using a 'two-mass' model for assessing patterns of ground-force application suggests Bolt's right and left legs may perform differently, defying scientific assumptions that asymmetry hinders performance. Unexpected and potentially significant asymmetry in the fastest human runner ever would help scientists better understand the basis of maximal running speeds.