We do not increase our speed by increasing our stride length
         (“stepping out”) as D'Arcy Thompson claimed

1. A simple experiment shows v­  f   
2. Geometric considerations show that the ratio s / l doesn't scale because q £ q_max :
3. Kinematics also limits q £ q_max :
   —that is, if we think of walking as a sequence of (short) pole vaults, the
   initial angle q can't be too great or we won't get over the top.