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First published online July 6, 2005
Journal of Experimental Biology 208, 2741-2751 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01702
The mechanics of jumping versus steady hopping in yellow-footed rock wallabies
1 Concord Field Station, Department of Organismic and Evolutionary Biology,
Harvard University, Cambridge, MA 02138, USA
2 Department of Environmental Biology, University of Adelaide, Adelaide, SA
5003, Australia
3 Structure and Motion Laboratory, The Royal Veterinary College, Hawkshead
Lane, North Mymms, Hatfield, AL9 7TA, UK
* Author for correspondence (e-mail: cmcgowan{at}oeb.harvard.edu)
Accepted 18 May 2005
The goal of our study was to explore the mechanical power requirements
associated with jumping in yellow-footed rock wallabies and to determine how
these requirements are achieved relative to steady-speed hopping mechanics.
Whole body power output and limb mechanics were measured in yellow-footed rock
wallabies during steady-speed hopping and moving jumps up to a landing ledge
1.0 m high (
3 times the animals' hip height). High-speed video recordings
and ground reaction force measurements from a runway-mounted force platform
were used to calculate whole body power output and to construct a limb
stiffness model to determine whole limb mechanics. The combined mass of the
hind limb extensor muscles was used to estimate muscle mass-specific power
output. Previous work suggested that a musculoskeletal design that favors
elastic energy recovery, like that found in tammar wallabies and kangaroos,
may impose constraints on mechanical power generation. Yet rock wallabies
regularly make large jumps while maneuvering through their environment. As
jumping often requires high power, we hypothesized that yellow-footed rock
wallabies would be able to generate substantial amounts of mechanical power.
This was confirmed, as we found net extensor muscle power outputs averaged 155
W kg–1 during steady hopping and 495 W kg–1
during jumping. The highest net power measured reached nearly 640 W
kg–1. As these values exceed the maximum power-producing
capability of vertebrate skeletal muscle, we suggest that back, trunk and tail
musculature likely play a substantial role in contributing power during
jumping. Inclusion of this musculature yields a maximum power output estimate
of 452 W kg–1 muscle.
Similar to human high-jumpers, rock wallabies use a moderate approach speed and relatively shallow leg angle of attack (45–55°) during jumps. Additionally, initial leg stiffness increases nearly twofold from steady hopping to jumping, facilitating the transfer of horizontal kinetic energy into vertical kinetic energy. Time of contact is maintained during jumping by a substantial extension of the leg, which keeps the foot in contact with the ground.
Key words: locomotion, jumping, hopping, muscle power, rock wallaby, Petrogale xanthopus
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