Mass-specific oxygen consumption (V˙O2) increases with movement speed. Postural costs (y-intercept) are affected by polar bear mass according to Equation 4. Larger bears are proportionately more efficient than smaller bears. Curves are based on predictions from the top model (exponential model; Equation 2), which when parameterized is: V˙O2 = (1.056 * mass−0.25) * e0.2626*S.