Page 26 - Eclipse - Autumn/Winter 2022

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, RVC Professor of or even decreases.
Evolutionary Biomechanics, and former From these findings, it was further
RVC 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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