Taylor Jessica, Deeming D Charles, Sutton Gregory P
School of Life & Environmental Sciences, University of Lincoln, Joseph Banks Laboratories, Green Lane, Lincoln LN6 7DL, UK.
J Exp Biol. 2024 Dec 15;227(24). doi: 10.1242/jeb.248018. Epub 2024 Dec 16.
Animals often leap from substrates that give way under them, such as leaves, soft ground or flexible branches. This provides an added complexity for latch-mediated spring-actuated (LaMSA) jumping animals because the spring-loaded system often works so quickly that neural feedback cannot adjust for errors caused by a yielding substrate. We studied a LaMSA jumper, the grasshopper, to determine how the mechanical properties of a substrate giving way under them would affect the kinematics of the jump. We measured this by allowing grasshoppers to leap from two diving boards, a long one that could generate a whole range of relative stiffnesses, and a shorter, much lighter, but stiffer board. Substrate stiffness was manipulated by then placing the grasshopper on different locations on that diving board, presenting from 30% of the grasshopper's leg stiffness to 200 times the grasshoppers leg stiffness. For platform stiffnesses that were less than that of the grasshopper, take-off velocity and kinetic energy were reduced, but jump elevation (the jump trajectory) was unaffected. For stiffnesses that were greater than that of the grasshopper, there was no effect on take-off velocity and kinetic energy. When jumping from an extremely light and stiff substrate, recoil of the surface allowed the grasshopper to recover some of the lost energy. Consequently, when jumping from substrates that are less stiff than they are (such as floppy leaves), grasshoppers must contend with lower take-off velocities, but jump direction is unaffected.
动物常常会从在它们身下塌陷的基质上起跳，比如树叶、松软的地面或柔韧的树枝。这给基于闩锁介导的弹簧驱动（LaMSA）的跳跃动物增添了复杂性，因为弹簧加载系统的工作速度往往极快，以至于神经反馈无法对由塌陷基质导致的误差进行调整。我们研究了一种LaMSA跳跃者——蚱蜢，以确定在其身下塌陷的基质的机械特性会如何影响跳跃的运动学。我们通过让蚱蜢从两个跳板上起跳来进行测量，一个是长跳板，它能产生一系列不同的相对刚度，另一个是短得多、轻得多但更硬的跳板。通过将蚱蜢放置在跳板上的不同位置来控制基质的刚度，其刚度范围从蚱蜢腿部刚度的30%到蚱蜢腿部刚度的200倍。对于刚度小于蚱蜢的平台，起跳速度和动能会降低，但跳跃高度（跳跃轨迹）不受影响。对于刚度大于蚱蜢的平台，起跳速度和动能没有受到影响。当从极其轻且硬的基质上起跳时，表面的反冲使蚱蜢能够恢复一些损失的能量。因此，当从比它们自身刚度小的基质（如柔软的树叶）上起跳时，蚱蜢必须应对较低的起跳速度，但跳跃方向不受影响。
