Telemetered in vivo strain analysis of locomotor mechanics of brachiating gibbons
Nature (1989) 342: 270-272
Sharon M. Swartz, John E.A. Bertram and Andrew A. Biewener

The slender elongated form that is characteristic of the forelimb long bones of
gibbons (Hylobates) has long been attributed to their functional adaptation to
habitual armswinging locomotion, although potential selective advantages of this
morphology for brachiation have yet to be demonstrated. If the forces exerted on
the limb skeleton during brachiation indeed differ greatly from those of other
locomotor modes, then the changes in skeletal loading accompanying a shift in
locomotor behaviour could favour alterations in skeletal morphology in brachiating
lineages. In vivo skeletal strain patterns recorded by using radiotelemetry during
brachiation indicate that the forelimb bones of the gibbon are loaded in substantial
tension and show reduced bending and compression in comparison with other
mammals. We suggest that this unique loading regime could have contributed to
the evolution of the distinctive morphology of hylobatid limbs.