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Scaling of the ankle extensor muscle-tendon units and the biomechanical implications for bipedal hopping locomotion in the post-pouch kangaroo Macropus fuliginosus

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dc.contributor.authorSnelling, E.
dc.contributor.authorBiewener, A.
dc.contributor.authorHu, Q.
dc.contributor.authorTaggart, D.
dc.contributor.authorFuller, A.
dc.contributor.authorMitchell, D.
dc.contributor.authorMaloney, S.
dc.contributor.authorSeymour, R.
dc.date.issued2017
dc.description.abstractBipedal hopping is used by macropods, including rat-kangaroos, wallabies and kangaroos (superfamily Macropodoidea). Interspecific scaling of the ankle extensor muscle-tendon units in the lower hindlimbs of these hopping bipeds shows that peak tendon stress increases disproportionately with body size. Consequently, large kangaroos store and recover more strain energy in their tendons, making hopping more efficient, but their tendons are at greater risk of rupture. This is the first intraspecific scaling analysis on the functional morphology of the ankle extensor muscle-tendon units (gastrocnemius, plantaris and flexor digitorum longus) in one of the largest extant species of hopping mammal, the western grey kangaroo Macropus fuliginosus (5.8-70.5 kg post-pouch body mass). The effective mechanical advantage of the ankle extensors does not vary with post-pouch body mass, scaling with an exponent not significantly different from 0.0. Therefore, larger kangaroos balance rotational moments around the ankle by generating muscle forces proportional to weight-related gravitational forces. Maximum force is dependent upon the physiological cross-sectional area of the muscle, which we found scales geometrically with a mean exponent of only 0.67, rather than 1.0. Therefore, larger kangaroos are limited in their capacity to oppose large external forces around the ankle, potentially compromising fast or accelerative hopping. The strain energy return capacity of the ankle extensor tendons increases with a mean exponent of ~1.0, which is much shallower than the exponent derived from interspecific analyses of hopping mammals (~1.4-1.9). Tendon safety factor (ratio of rupture stress to estimated peak hopping stress) is lowest in the gastrocnemius (< 2), and it decreases with body mass with an exponent of -0.15, extrapolating to a predicted rupture at 160 kg. Extinct giant kangaroos weighing 250 kg could therefore not have engaged in fast hopping using 'scaled-up' lower hindlimb morphology of extant western grey kangaroos.
dc.description.statementofresponsibilityEdward P. Snelling, Andrew A. Biewener, Qiaohui Hu, David A. Taggart, Andrea Fuller, Duncan Mitchell, Shane K. Maloney and Roger S. Seymour
dc.identifier.citationJournal of Anatomy, 2017; 231(6):921-930
dc.identifier.doi10.1111/joa.12715
dc.identifier.issn0021-8782
dc.identifier.issn1469-7580
dc.identifier.orcidHu, Q. [0000-0003-3163-7859]
dc.identifier.orcidTaggart, D. [0000-0001-7251-8018]
dc.identifier.orcidSeymour, R. [0000-0002-3395-0059]
dc.identifier.urihttp://hdl.handle.net/2440/110157
dc.language.isoen
dc.publisherWiley
dc.relation.granthttp://purl.org/au-research/grants/arc/DP120102081
dc.rights© 2017 Anatomical Society
dc.source.urihttps://doi.org/10.1111/joa.12715
dc.subjecthopping
dc.subjectkangaroo
dc.subjectmuscle
dc.subjectstrain
dc.subjectstress
dc.subjecttendon
dc.titleScaling of the ankle extensor muscle-tendon units and the biomechanical implications for bipedal hopping locomotion in the post-pouch kangaroo Macropus fuliginosus
dc.typeJournal article
pubs.publication-statusPublished

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