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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

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The mechanics of jumping versus steady hopping in yellow-footed rock wallabies

C. P. McGowan^1,*, R. V. Baudinette^2,, J. R. Usherwood³ and A. A. Biewener¹

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

View larger version (10K): [in a new window]   Fig. 1. A schematic of the runway used to collect jumping trials showing the position of the force plate, the height of the jump and rock wallaby's actual body size relative to the jump. The first outline (i) and the last outline (ii) are representative of the frames chosen to calculate initial velocity conditions (see text for details).

View larger version (21K): [in a new window]   Fig. 2. Mean ground reaction force (GRF) data for steady-speed hopping (gray) and jumping (black). (A) The GRF vector is shown relative to the rock wallaby's average body position, leg angle (broken line) and estimated CoM position during stance. (B) Mean GRF recordings in body weights (BW) plotted against percent of stance. (C) Vertical and horizontal stance impulses. Horizontal impulses are divided in to negative (–), positive (+) and net (patterned bars) impulses. Dotted lines (B) and error bars (C) indicate S.E.M.

View larger version (23K): [in a new window]   Fig. 3. Mean changes in (A) gravitational potential energy (PE), (B) vertical kinetic energy (KEvert), (C) horizontal kinetic energy (KEhoriz) and (D) total energy (Etot) during stance, plotted for steady-speed (gray) and jumping (black) trials. Dotted lines indicate S.E.M.

View larger version (22K): [in a new window]   Fig. 4. Mean power and work produced during steady speed (gray) and jumping (black) trials. (A) Power output during stance normalized to body mass (left y axis) and hind limb extensor muscle mass (right y axis). Horizontal broken lines represent the mean power produced during stance. (B) Negative (–), positive (+) and net (patterned bars) muscle mass-specific work produced during stance. Dotted lines (A) and error bars (B) indicate S.E.M.

View larger version (14K): [in a new window]   Fig. 5. A schematic of the virtual leg model representing the mean values for the variables measured during steady-speed (gray) and jumping (black) trials. (A) Leg angle of attack (on), leg angle at take-off (off), and the CoM velocity vector at take-off (v). The arrows represent the relative magnitude and angle () of velocity vector. (B,C) Initial leg length (L0), path of the CoM (thick broken line), path of the of the CoM if the leg did not compress (thin broken line) and the point of maximum leg compression (Lmax), as a function of normalized stance time (T) for steady-speed (B) and jumping (C) trials. The relative angles of the legs shown are representative of the mean leg angles observed, as is the relative amount of leg extension measured at take-off (Lext).