CARLSON, Kristian J.; Universit�t Z�rich-Irchel: Modelling arboreal locomotion: the effect of limb abduction on substrate reaction forces during lemurid quadrupedal locomotion.

Arboreal locomotion requires movement through three-dimensional settings in which substrates and superstrates are irregularly positioned. As a consequence, animals adopt a variety of limb postures during locomotion, often abducting limbs at proximal joints. Studies of external forces during simulated arboreal locomotion, however, typically examine a limited subset of locomotor diversity observed among free-ranging animals. While comparisons of arboreal and terrestrial linear locomotion have shown lower external forces during arboreal locomotion, likely due to compliant gait, the mediolateral (ML) component of the substrate reaction force (SRF) may reflect degree of limb abduction (i.e., greater during terrestrial linear locomotion). To investigate this, SRFs and degree of limb abduction at shoulder and hip joints were recorded for 390 limb contacts of lemurids (Eulemur rubriventer). Individuals traveled along a wooden runway or linear pole, each with an instrumented segment, and the same pole, but with the instrumented section offset from the longitudinal axis of the pole. As offset increased, ML peak force magnitude increased. At the greatest offset, magnitudes and directions of ML peak forces were similar to those observed during runway locomotion, despite slower average speed. When the instrumented segment was offset to any degree, the SRF usually switched to medially-directed, unlike the laterally-directed force usually observed during simulated arboreal locomotion on the linear pole. Mediolateral peak force magnitudes experienced during arboreal locomotion can be high, even exceeding those experienced during terrestrial locomotion. Supported by NSF BCS 0411489.