Response: Of ideas, dichotomies, methods, and data – how much do elephant kinematics differ from those of other large animals?

Hutchinson, John R.

doi:10.1242/jeb.025098

Cited by 7 publications

(9 citation statements)

References 7 publications

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“…Our study reveals that elephants have quite compliant limbs, not as stiff and columnar as previously envisaged (1)(2)(3)(4)17), that give a smooth ride to the CoM (6) and keep peak GRFs low (11)(12)(13). To achieve the observed limb compliance and low peak GRFs, elephants synchronize their limb dynamics in the vertical direction, but they incur considerable mechanical costs from limbs working against each other horizontally (27).…”

Section: Resultssupporting

confidence: 48%

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Integration of biomechanical compliance, leverage, and power in elephant limbs

Ren

Miller

Lair³

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

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106

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The structure and motion of elephant limbs are unusual compared with those of other animals. Elephants stand and move with straighter limbs (at least when walking), and have limited speed and gait. We devised novel experiments to examine how the limbs of elephants support and propel their mass and to explore the factors that may constrain locomotor performance in these largest of living land animals. We demonstrate that elephant limbs are remarkably compliant even in walking, which maintains low peak forces. Dogma defines elephant limbs as extremely "columnar" for effective weight support, but we demonstrate that limb effective mechanical advantage (EMA) is roughly one-third of that predicted for their size. EMA in elephants is actually smaller than that in horses, which are only one-tenth their mass; it is comparable to human limb values. EMA drops sharply with speed in elephants, as it does in humans. Muscle forces therefore must increase as the limbs become more flexed, and we show how this flexion translates to greater volumes of muscle recruited for locomotion and hence metabolic cost. Surprisingly, elephants use their forelimbs and hindlimbs in similar braking and propulsive roles, not dividing these functions among limbs as was previously assumed or as in other quadrupeds. Thus, their limb function is analogous to fourwheel-drive vehicles. To achieve the observed limb compliance and low peak forces, elephants synchronize their limb dynamics in the vertical direction, but incur considerable mechanical costs from limbs working against each other horizontally.lephants have unusual limb structure and function. They use walking footfall patterns, have seemingly straightened limbs, and lack an aerial phase in their stride throughout their speed range (1-7). However, at faster speeds, they switch to biomechanical running (i.e., bouncing; refs. 8, 9), without a discrete gait transition (4-7, 10). Elephants also seem unable to exceed speeds of ∼7 ms −1 (15 mph) (1-5). These odd features relate to elephants' massive size and thus have broader comparative relevance, but they remain unexplored in a deeper biomechanical context. These features suggest that elephants do not use their limbs in the same mechanical ways as typical quadrupeds do, perhaps involving considerable limb compliance (11-13). In the present study, we examined how elephant forelimbs and hindlimbs function across a wide range of speeds, and compared these mechanical functions with those of other animals.Furthermore, elephants are particularly relevant to a major biomechanical concept regarding the relationship of body size and the limbs' effective mechanical advantage [EMA; the amount of ground reaction force (GRF) generated at the foot per unit muscle force, or simply "overall leverage"] (Fig. 1A). EMA is proportional to the moment arm of each joint's muscle force divided by the moment arm of the GRF about that joint (14-16). Larger animals tend to increase their EMA mainly by straightening their limbs, thereby reducing GRF moment arms. This helps ...

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Section: Resultssupporting

confidence: 48%

“…Horse limbs are already almost as straight as feasible (15,17), and thus have an EMA near the probable limit. Orientation of the GRF vector and position of the center of pressure are other important components of EMA.…”

Section: Resultsmentioning

confidence: 99%

Integration of biomechanical compliance, leverage, and power in elephant limbs

Ren

Miller

Lair³

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

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106

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“…Small mammals have a crouched locomotion posture with rather flexed limb joints but the posture becomes increasingly more upright in larger mammals so that limb elements become more nearly aligned with the ground reaction force (Fig.2). Very big terrestrial animals, like elephants, walk on rather straight legs, sometimes termed columnar legs, with the limb segments supposedly taking up a nearly columnar posture, a so-called graviportal adaptation (Hildebrand, 1985;Hildebrand and Hurley, 1985) -although locomotion in elephants does involve more limb flexion than traditionally thought (Ren et al, 2008;Hutchinson, 2009).…”

Section: Terrestrial Mammalsmentioning

confidence: 99%

Scaling for stress similarity and distorted-shape similarity in bending and torsion under maximal muscle forces concurs with geometric similarity among different-sized animals

Norberg

Aldrin

2010

Journal of Experimental Biology

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SUMMARY When geometric similarity, or isometry, prevails among animals of different sizes their form and proportions are similar. Weight increases as the cube of the length dimension, while cross-sectional areas increase as its square, so in load-bearing structural elements the stress, caused by the body weight, increases in direct proportion to the length dimension, both for pure axial loads and for transverse bending and torsional loads. On this account, large body sizes would be expected to set up compensatory selection on the proportions of supporting structures, making them disproportionately thicker as required to maintain similar, size-independent safety factors against breakage. Most previous scaling theories have assumed that the strength of support elements has evolved with respect to loads due to the body weight. But then, from the arguments above, a scaling principle different from the geometric similarity rule would be required in order for safety factors to remain similar among different-sized animals. Still, most comparable animals of ‘similar kind’ scale in accordance with the geometric similarity rule. Here, we instead argue that muscle forces cause much larger loads on structural support elements during maximum performance events (such as during prey capture or escape from predators) than do loads dictated by the body weight (such as during cruising locomotion), and that structural strength therefore might evolve with respect to maximal muscle forces rather than to the body weight. We explore how the transverse and longitudinal lengths of structural support elements must scale to one another, and to muscle transverse length, in order to satisfy each of the following, functionally based, similarity principles for support elements placed in bending, or in torsion, by maximal muscle forces during locomotion: (1) similarity in axial stress, or (2) in torsional shear stress, and (3) similarity in bent shape, or (4) in twisted shape. A dimensional relationship that satisfies all four conditions actually turns out to be the geometric similarity rule. These functional attributes may therefore help to explain the prevalence of geometric similarity among animals. Conformance of different-sized species with the geometric similarity principle has not been directly selected for as such, of course, but may have arisen as a by-product of adaptation in morphological proportions, following upon selection, in each separate species-lineage, for adequate and similar safety factors against breakage, and similar optimal distorted shapes, of structural support elements placed in bending, or in torsion, by maximal muscle forces.

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“…Reasons for low EMA values in Giraffa can be ascribed to the magnitudes of the GRF and/or muscle moment arms. With regard to GRF moment arms, animals larger than horses probably are unable to align their GRF vector even closer to their joint centers to minimize R and maximize EMA (21), via increased straightening of the limb. In the case of the giraffe, our comparisons between closely related giraffid species suggest that their long segment lengths and shoulder height (and thus “cursorial” limb morphology) predispose them to exaggerated GRF moment arms (Figure 4A).…”

Section: Discussionmentioning

confidence: 99%

Low effective mechanical advantage of giraffes’ limbs during walking reveals trade-off between limb length and locomotor performance

Basu

Hutchinson

2021

Preprint

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Giraffes (Giraffa camelopardalis) possess specialised locomotor morphology, namely elongate and gracile distal limbs. Whilst this contributes to their overall height (and enhanced feeding behaviour), we propose that the combination of long limb segments and modest muscle lever arms results in low effective mechanical advantage (EMA, the ratio of in-lever to out-lever moment arms), when compared with other cursorial mammals. To test this, we used a combination of experimentally measured kinematics and ground rection forces (GRFs), musculoskeletal modelling, and inverse dynamics to calculate giraffe forelimb EMA during walking. Giraffes walk with an EMA of 0.34 (±0.05 S.D.), with no evident association with speed within their walking gait. Giraffe EMA was markedly below the expectations extrapolated from other mammals ranging from 0.03 – 297 kg, and provides further evidence that EMA plateaus or even diminishes in mammals exceeding horse size. We further tested the idea that limb segment length is a factor which determines EMA, by modelling the GRF and muscle moment arms in the extinct giraffid Sivatherium giganteum and the other extant giraffid Okapia johnstoni. Giraffa and Okapia shared similar EMA, despite a 4-6 fold difference in body mass (Okapia EMA = 0.38). In contrast Sivatherium, sharing a similar body mass to Giraffa, had greater EMA (0.59), which we propose reflects behavioural differences, such athletic performance. Our modelling approach suggests that limb length is a determinant of GRF moment arm magnitude, and that unless muscle moment arms scale isometrically with limb length, tall mammals are prone to low EMA.Significance StatementGiraffes are the tallest living animals - using their height to access food unavailable to their competitors. It is not clear how their specialized anatomy impacts their athletic ability. We made musculoskeletal models of the forelimbs from a giraffe and two close relatives, and used motion-capture and forceplate data to measure how efficient they are when walking in a straight line. A horse for example, uses just 1 unit of muscle force to oppose 1 unit of force on the ground. Giraffe limbs however are comparatively disadvantaged – their muscles must develop 3 units of force to oppose 1 unit of force at the ground. This explains why giraffes walk and run at relatively slow speeds.

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Response: Of ideas, dichotomies, methods, and data – how much do elephant kinematics differ from those of other large animals?

Cited by 7 publications

References 7 publications

Integration of biomechanical compliance, leverage, and power in elephant limbs

Integration of biomechanical compliance, leverage, and power in elephant limbs

Scaling for stress similarity and distorted-shape similarity in bending and torsion under maximal muscle forces concurs with geometric similarity among different-sized animals

Low effective mechanical advantage of giraffes’ limbs during walking reveals trade-off between limb length and locomotor performance

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