and (3) a double-exponential model that allows metabolism to more flexibly scale with speed, (3)V˙O2=PebSc; where P is polar bear postural cost (i.e. the energetic cost of maintaining an upright posture when speed is zero), e is the natural log (2.718…), and b and c are exponents that describe the rates at which oxygen consumption changes with movement speed (S). From previous work (Hurst et al., 1982b), postural costs are known to depend on mass. Thus, in all models we fixed the postural costs at the expected values for each polar bear mass based on the equation of Hurst et al. (1982b), following Taylor et al. (1970): (4)P=1.056×mass−0.25.