Introduction

There are relatively few biomechanical studies of the quadrupedal walking of primates, especially that of the apes. This is almost certainly because of the extreme difficulty of obtaining records of voluntary (and hence naturalistic) behavior, of even the most common elements of a species' locomotor repertoire, since only that which happens to occur on the measuring equipment used to gather force data (and/or within the field of view of the equipment used to gather motion data) can be analyzed. For this reason, and because of the additional danger of the subjects (or the weather!) damaging equipment, the literature primarily contains studies of trained or guided animals (most often subadult), which are usually based on small sample sizes.

The primates as a whole are generally agreed to be hind-limb dominated (e.g., Martin, 1990), and Rollinson and Martin (1981) used this phenomenon to explain the diagonal gaits which are another remarkable characteristic of primate quadrupedalism. However, their study did not consider the force exerted during walking. One of the first comprehensive studies to do so, by Kimura et al. (1979), compared the chimpanzee and orangutan to three nonhominoid species. Their findings led them to propose that while both primates and nonprimates primarily use the forelimbs to control the direction of movement (i.e., they are both “forelimb steered”), primates bear a greater proportion of vertical forces on the hind limb and are “hind limb driven.” In contrast, bearing more force on the forelimbs, other mammals are “forelimb driven.”