DONELAN, JM*; RODOREDA, S; GRABOWSKI, A; KRAM, R; DAWSON, TJ; Univ. of Alberta, Edmonton; Univ. of New South Wales, Sydney; Univ. of Colorado, Boulder; Univ. of Colorado, Boulder; Univ. of New South Wales, Sydney: Metabolic energetics and biomechanics of pentapedal locomotion in Red Kangaroos

Kangaroos (Macropoidea) move in a biomechanically interesting way at slow speeds; they walk pentapedally using their tail to “crutch” along. Early work by Dawson and Taylor (1973) on two Red Kangaroos (Macropus rufus) suggested that this mode of locomotion is metabolically expensive. Despite the apparent expense, kangaroos largely rely on their pentapedal gait to forage and graze. To extend the work of Dawson and Taylor, we studied the metabolic energetics of pentapedal walking in seven Red Kangaroos. We trained the animals to wear a mask and walk on a treadmill at a range of speeds (0.25�1.0 m/s). This allowed us to measure metabolic power using open-flow indirect calorimetry. On average, the gross metabolic power required to walk pentapedally at 0.25 m/s was 4.9 � 1.3 W/kg (mean � std) and increased to 12.3 � 0.5 W/kg at 1.0m/s. In comparison to walking in bipeds and quadrupeds of similar mass, pentapedal walking in kangaroos requires ~2.6 times the metabolic power. One possible explanation for the relative expense of pentapedal walking is that this gait requires the performance of an unusually large amount of mechanical work. To test this hypothesis, we trained the same animals to walk along a walkway and across a force platform. A video camera recorded sagittal plane motion. By combining video and ground reaction force data, the mechanical work required to walk pentapedally can be calculated. In addition, this methodology allows us to determine the relative contributions of the fore limbs, hind limbs and, in particular, the tail to the dynamics of pentapedal walking. We are currently analyzing our biomechanical data.