In conclusion we can see that, contrary to early and common beliefs arm action is essential and important to running. Their motion makes a small, but critical contribution to lift, which increases as running speed does. When we focus on the center of mass of the body, the arms decrease the horizontal excursions of this point, in both side to side and forward directions. This allows the athlete to maintain more constant horizontal velocity. Therefore resulting in a lowered energy cost , which could be crucial during a distance race. Interestingly enough, the arm action that is most important to running is not the obvious back and forth motion, but the acceleration of the arm, effecting lift and momentum.