Page 26 - Eclipse - Autumn/Winter 2022

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Page 26 - Eclipse - Autumn/Winter 2022
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Long limb limitations





               VC research has revealed new   giraffes’ limbs is extreme, and although
               insights into giraffe mobility   this aids feeding from trees, it may not
               and how the efficiency of    increase athleticism.
       Rmovements in relation to body       Instead, the study found that giraffes’
        mass appears to plateau amongst     effective mechanical advantage, a
        animals of a certain size. These findings   measure of limb efficiency in producing
        contradict what is commonly assumed   muscle forces, was four times less than
        for many mammals – that possessing   would have been expected based on
        long, straight limbs necessarily    data extrapolated from a range of similar
        confers a mechanical advantage which   animals. This indicates giraffes’ muscles
        enhances speed and muscle efficiency.
                                            have to generate relatively high forces to
        The study, which was published in   conduct behaviours that a smaller animal,
        Proceedings of the National Academy   even a horse, can do more effectively.
        of Sciences, was conducted by creating   Comparing the three species tested,
        3D musculoskeletal models of the    the researchers also determined that
        forelimbs of giraffes and two related   the effective mechanical advantage
        species, the living okapi (Okapia   varied. For example, while the giraffe and
        johnstoni), known as the “forest    Sivatherium giganteum have similar body
        giraffe” found in Central Africa, and   mass, the giraffe had lower effective
        the extinct Sivatherium giganteum,   mechanical advantage. Meanwhile, the
        one of the largest known giraffes, from   giraffe and okapi had similar effective
        the Himalayan foothills more than two   mechanical advantage, despite the
        million years ago. The researchers then   giraffe having four to six times the body   Giraffes’ long limbs may help them feed from
        used motion capture and force data to   mass of an okapi. This suggests that   tall tree canopies, but their extreme height
        measure muscle efficiency for walking   past a certain size, approximately that   may constrain their athletic capabilities.
        giraffes while estimating the efficiency   of a horse, the increase in effective
        of the other two species.
                                            mechanical advantage associated
        Together, the researchers, led by   with a greater body mass plateaus
        John Hutchinson, şÚÁĎÉç Professor of   or even decreases.
        Evolutionary Biomechanics, and former   From these findings, it was further
        şÚÁĎÉç PhD student Dr Christopher Basu,   concluded that taller animals are only
        now a Lecturer in Veterinary Anatomy at   likely to have greater effective mechanical
        the University of Surrey, found that the   advantage if the distance between the
        assumed advantages for increasing mass   muscle and the pivot point of the joint is
        and limb length in mammals do not apply   proportional to their limb length.
        to giraffes. This is because the length of


          Modelled midstance
          postures of left forelimbs
          of Okapia, Sivatherium
          and Giraffa. Models are
          displayed to scale, with
          each gray box measuring
          0.5 m in length.












                                                                    Christopher Basu and John Hutchinson collected
                                                                    motion and force data from walking giraffes, in
                                                                    collaboration with the Zoological Society of London, UK.


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