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First published online May 18, 2006
Journal of Experimental Biology 209, 2042-2049 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02235

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Adaptive value of ambling gaits in primates and other mammals

Daniel Schmitt¹, Matt Cartmill^1,*, Timothy M. Griffin², Jandy B. Hanna¹ and Pierre Lemelin³

¹ Department of Biological Anthropology and Anatomy, Duke University, Durham, NC 27710, USA
² Orthopaedic Bioengineering Laboratory, Department of Surgery, Duke University Medical Center, Durham, NC 27710, USA
³ Division of Anatomy, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, T6G 2H7, Canada

View larger version (23K): [in a new window]   Fig. 1. Ambling gait cycle in an Asian elephant (Elephas maximus) (top) [traced from images in (Gambaryan, 1974)] and a fat-tailed dwarf lemur (Cheirogaleus medius) (bottom) (traced from our videotape). Note that during an ambling gait cycle, a single forelimb (FL) or hindlimb (HL) provides support for the entire body while all the other limbs are off the substrate. Mirror-image (R/L) inversions in limb pairs between the two species at corresponding phases of the cycle reflect the difference between the lateral-sequence amble of the elephant and the diagonal-sequence amble of the lemur.

View larger version (19K): [in a new window]   Fig. 2. Modified Hildebrand diagram showing distribution of the 295 gait cycles for which diagonality (D) and duty factor (Sf) were calculated (i.e. in which deviations from symmetry were 10% or less for both forelimbs and hindlimbs). Gait cycles plotted within the blue triangles lack a whole-body aerial phase. In the upper blue triangle (diagonality >50%), animals are using diagonal-sequence ambles. In the lower blue triangle (diagonality <50%), animals are using lateral-sequence ambles. Rectangular bands indicate running trots (in red) (diagonality equal to or near 50%) and paces (in yellow) (diagonality equal to or near 100% or 0%). The diagonal black line represents the equation diagonality=100-forelimb Sf [forelimb duty factor is the relevant duty factor in this case, based on the mathematical model used (Cartmill et al., 2002)]. Those gait cycles plotting directly on that line have maximal duration of bipedal support periods. Primate ambling strides plot above but close to the line, thus eliminating the whole-body aerial phase while preserving near-maximal periods of bipedal support. Note that some of the data represent running trots (mostly for Callithrix jacchus).

View larger version (21K): [in a new window]   Fig. 3. Empirical and modeled vertical ground reaction forces and displacements of the center of mass. (A) Empirical vertical ground reaction force data for Cheirogaleus medius (body mass=180 g) while ambling at 1.2 m s-1along a 28 mm diameter pole. Thin lines correspond to the individual limb forces and the thick line is the total (i.e. summed) force. The black thin line represents the left fore- and hindlimb forces obtained from sequential, overlapping footfalls on a pole segment connected to a force platform. The left limb forces were replicated a half-cycle out of phase to obtain right limb forces (gray lines). Individual limb forces were modeled following the mathematical model used (McNeill Alexander and Jayes, 1978) using empirical values for body mass and duty factor. (B) Model forces reconstructed for a whole stride for a diagonality of 63% (i.e. the diagonality used by C. medius in A). (C) Model forces reconstructed for a diagonality of 50% (i.e. a running trot). Horizontal bars below the reaction forces represent the footfall patterns (RH=right hindlimb, LF=left forelimb, LH=left hindlimb, and RF=right forelimb). The vertical displacements of the center of mass corresponding to the vertical force data in A-C are shown in D-F, respectively. Displacement data were calculated following published methods (Cavagna, 1975).

View larger version (69K): [in a new window]   Fig. 4. Vertical displacement of the center of mass across a range of different diagonality and duty factor combinations, computed from a mathematical model of the vertical component of the force exerted by the foot on the ground (McNeill Alexander and Jayes, 1978). Vertical-displacement data are presented for diagonalities of 50-75% and duty factors of 50-25%. Empirical data (black dots) are plotted at the actual diagonality: duty factor combinations used by the primates in our sample. Ambling results in smaller vertical oscillations of the center of mass because the individual limb forces are more uniformly distributed throughout the stride, which reduces the peak force acting on the body.