Meeting Abstract
4.4 Tuesday, Jan. 4 Preventing Damage: Absorbtion of Kinetic Energy in Locust Kicks SUTTON, GP*; BURROWS, M; University of Cambridge; University of Cambridge RScealai@gmail.com
While it is well known that insects use cuticular springs to store and quickly release energy, we will show that they also use cuticular springs to absorb and dissipate energy. When locusts kick they channel huge amounts of kinetic energy through their joints. If the kick misses the target, the leg extends extremely quickly to its maximum extent, which could result in a huge amount of shock at the femur/tibia (‘knee’) joint. To prevent this shock, the cuticle of the tibia has a semi-elastic buckling zone just proximal to the joint. Once the femur/tibia joint of a kicking locust reaches its maximum extension, the tibia bends at this buckling zone, sometimes by as much as 85 degrees. The tibia then returns to its original shape, dissipating a large fraction of the excess kinetic energy. After such a seemingly catastrophic bend, the locust can still kick and jump normally. By using high-speed video of kicking locusts, we have quantified the amount of kinetic energy in the kick, and show that it is correlated with the amount of subsequent bend in the leg. We then used a servomotor system to measure how much energy is absorbed and subsequently released by the amount of bending observed in vivo. The bends observed in vivo absorbed 80% of the energy present in the kick. Of this absorbed energy, 70% of it was dissipated within the buckling zone, and the last 30% was recovered. If the tibia was then bent a second time, the tibia absorbed 30% less energy, but there were no additional decrements for additional bends past the second. If the experiment was repeated 24 hours later, the tibia absorbed just as much energy as it did initially, indicating that this decrement was not caused by damage. Suprisingly, we found that the energy absorbtion was independent of how quickly we bent the leg. The tibial buckling zone thus acts as a velocity-independent shock absorber, absorbing and dissipating excess kinetic energy.
