O’NEILL, M.C.*; SCHMITT, D.; Johns Hopkins University School of Medicine; Duke University: Joint work and power associated with stance versus swing phase in running ring-tailed lemurs

Most quadrupedal animals, including primates, increase their metabolic cost of locomotion with increasing speed. Recent studies indicate that this is due to changes in muscle activation and recruitment patterns during both stance and swing phases, with swing phase muscle activity accounting for as much as 30 percent of the energetic cost of steady, level running. A broad overview of how limb muscle and muscle-tendon units modulate energy use can be obtained from an analysis of muscle mechanical advantage, work and power output. This study examines which muscle groups are responsible for adjusting limb force production, joint work and power across a range of running speeds in ring-tailed lemurs. Four adult ring-tailed lemurs, Lemur catta (2 males, 2 females; 2.2 to 2.8kg body mass), were studied at the Duke University Primate Center. Animals were trained to walk and run along a 12m x 1m runway constructed along a level stretch of outdoor paddock. The runway was instrumented with a 0.6m x 0.4m force platform; animals were video recorded in 2D using a high-speed (250 Hz) digital camera. Inverse dynamics was used to calculate the ground reaction force and limb inertia based moments, instantaneous power (W) and total work (Jkg-1) at each limb joint. The results of this study are discussed in the context of sources of mechanical power for increasing speed and their relationship to the energetic cost of locomotion. These data represent a first step in understanding how an animal designed for maximizing net power output maintains a reasonable locomotor economy for steady running. Supported by NSF-BCS 0525034, 452217