KINETICS OF LEAPING PRIMATES - INFLUENCE OF SUBSTRATE ORIENTATION ANDCOMPLIANCE

Our current knowledge about the forces leapers generate and absorb is very limited and based exclusively on rigid force platform measurement s. In their natural environments, however, leapers take off and land o n branches and tree trunks, and these may be compliant. We evaluated t he influence of substrate properties on leaping kinetics in prosimian leapers by using a combined field and laboratory approach. Tree sway a nd the timing of takeoffs relative to the movements of trees were docu mented for animals under natural conditions in Madagascar. Field data collected on three species (Indri indri, Propithecus diadema, Propithe cus verreauxi) indicate that in the majority of takeoffs, the substrat e sways and the animals takeoff before the elastic rebound of the subs trate. This implies that force is ''wasted'' to deform supports. Takeo ff and landing forces were measured in an experimental setting with a compliant force pole at the Luke University Primate Center. Forces wer e recorded for 2 Propithecus verreauxi and 3 Hapalemur griseus. Peak t akeoff forces were 9.6 (P. verreauxi) and 10.3 (H. griseus) times body weight, whereas peak landing forces were 6.7 (P. verreauxi) and 8.4 ( H. griseus) times body weight. As part of the impulse generated does n ot translate into leaping distance but is used to deform the pole, gre ater effort is required to reach a given target substrate, and, conseq uently, takeoff forces are high. The landing forces, on the other hand , are damped by the pole/substrate yield that increases the time avail able for deceleration. Our results contrast with previous studies of l eaping forces recorded with rigid platform measuring systems that usua lly report higher landing than takeoff forces. We conclude that 1) Lea pers generate and are exposed to exceptionally high locomotory forces. The takeoff forces are higher than the landing forces when using comp liant supports, indicating that the takeoff rather than the landing ma y be critical in interpreting leaping behavior and related aspects of musculoskeletal design. 2) Large-bodied vertical clingers and leapers do not usually take advantage of the elastic energy stored in substrat es. Rather, force (and energy) is wasted to deform compliant supports. 3) A compliant force pole approximates the conditions faced by large- bodied vertical clingers and leapers in the wild more closely than do rigid force platforms. (C) 1995 Wiley-Liss, Inc.