Meeting Abstract
Coordinating forces in a multi-jointed limb challenges biological and artificial walking systems alike. Joints of a limb have to act together to propel the body, stabilize it against gravity, and adjust locomotion to changes in the environment. Studies on insects have provided many insights into the neuromechanics underlying joint control, but little is known about how insect leg joints actually contribute to locomotion when movements are unrestrained and under body load. To further our understanding, we analyzed joint moments in intact, freely walking stick insects. Joint moments were derived from rigid link models of all limbs by combining three-dimensional high-speed motion capture with single leg force recordings. Unexpectedly, we found that the coxa-trochanter joint (part of the “hip”), primarily responsible for providing support, was generally also responsible for modulating propulsion. Large supporting moments at this joint concurrently reduced propulsion at the beginning of stance and increased it toward the end. In the other leg joints, stabilizing forces dominated propulsive forces. Notably, these moments did not necessarily follow fixed patterns. They were particularly variable at the middle leg’s femur-tibia (“knee”) joint, with a high sensitivity to the leg’s extension–presumably to counteract deviations from an orthogonal leg posture. This motor flexibility may arise from strict feedback control involving dedicated force sensors (campaniform sensilla) for each joint. Future studies with manipulated sensory input may help us unravel their importance for walking control and inspire control algorithms for multi-jointed robotic legs.
