Limb excursion during quadrupedal walking: How do primates compare to other mammals?

Primate quadrupeds are said to use relatively large limb excursions for mammals of their body size. Until recently, this claim was based on a comparison of hindlimb excursion data derived from small samples of primates and non-primates. Using video recordings collected at zoos and primate research centres, the present study documents this contrast on much wider samples of quadrupedal mammals. The results indicate that while on average hindlimb excursion is relatively larger in quadrupedal primates, this contrast is somewhat less dramatic than first reports suggested. Comparisons between the data reported here and previously collected forelimb excursion data reveal a surprising asymmetry between the fore- and hind excursions for most mammalian species. Most commonly, forelimb excursion exceeds that of the hindlimb. We suggest that this is related to a complementary asymmetry in limb length (forelimbs shorter than hind) for the purpose of achieving equal step lengths for both pairs of limbs. Relatively large hindlimb excursions in primates have been related to a mechanism that reduces stresses on the forelimbs and then recovers mechanical energy during gait. We suggest that large excursions of both the fore- and hindlimbs are linked to other alterations in gait parameters, such as step length, contact time, and limb compliance, that have been adopted in quadrupedal primates to facilitate locomotion along slender arboreal substrates.