Fig. 3. Inverted pendulum mechanics of the center of mass for dogs walking at a range of speeds. (A) Recovery of mechanical energy via the inverted pendulum mechanism (recovery=–117.5u²+213.6u–27.1, where u is speed; r²=0.38). (B) Mass-specific work performed on the center of mass per distance traveled (W_com=0.407u²–0.718u+0.440; r²=0.39). (C) Mass-specific mechanical work per unit distance to lift (E_p; filled circles) and accelerate (E_k; open circles) the center of mass (E_p=0.088u²–0.236u+0.332, r²=0.88; E_k=–0.153u²+0.412u–0.032, r²=0.88). (D) Phase difference between the fluctuations in E_p and E_k (phase=–75.5u²+62.7u+196.4; r²=0.44). Values are means ± S.E.M. for all of the dogs. Lines are least-squares regressions.