Aerts P, Ker R F, De Clercq D, Ilsley D W, Alexander R M
Department of Biology, Antwerp University (UIA), Wilrijk, Belgium.
J Biomech. 1995 Nov;28(11):1299-308. doi: 10.1016/0021-9290(95)00009-7.
In vivo and in vitro mechanical testing of the human heel pad gave apparently different properties for this structure: the in vivo stiffness is about six times lower, whereas the percentage of energy dissipation is about three times higher (up to 95% loss). It was postulated that this divergence must be ascribed to the lower leg being involved in in vivo heel pad testing. This hypothesis is presently evaluated by applying the two experimental procedures formerly used in the in vivo (an instrumented pendulum) and in vitro (an Instron servo-hydraulic testing machine) investigations on the same isolated heel pad samples. Instron load-deformation cycles mimicking pendulum impacts (i.e. 'first loop-half cycles') are first evaluated and then compared to real pendulum impacts. When performed properly, the pendulum test procedure reveals the same mechanics for isolated heel pads as the Instron does. The load-deformation loops are basically identical. Thus similar non-linear stiffnesses (about 900 kN m-1 at body weight) and comparable amounts of energy dissipation (46.5-65.5%) are found with both types of test, still being largely different from the former in vivo results (150 kN m-1 and 95%, respectively). Therefore, the present findings support the hypothesis that the presence of the entire lower leg in in vivo tests indeed influences the outcome of the measurements. It must be concluded that the previously published in vivo data, if interpreted for the heel pad alone, implied not only an incorrectly low resilience but also a value far too low for stiffness.
对人体足跟垫进行的体内和体外力学测试显示，该结构具有明显不同的特性：体内刚度约低六倍，而能量耗散百分比约高三倍（高达95%的损耗）。据推测，这种差异必定归因于在体内足跟垫测试中涉及了小腿。目前通过对相同的孤立足跟垫样本应用先前在体内（仪器化摆锤）和体外（英斯特朗伺服液压试验机）研究中使用的两种实验程序来评估这一假设。首先评估模拟摆锤冲击的英斯特朗载荷 - 变形循环（即“第一个半循环”），然后将其与实际摆锤冲击进行比较。如果操作得当，摆锤测试程序显示出与英斯特朗测试相同的孤立足跟垫力学特性。载荷 - 变形循环基本相同。因此，两种测试都发现了相似的非线性刚度（体重下约为900 kN m -1）和相当的能量耗散量（46.5 - 65.5%），但仍与先前的体内结果（分别为150 kN m -1和95%）有很大差异。所以，目前的研究结果支持这样的假设，即在体内测试中整个小腿的存在确实会影响测量结果。必须得出结论，如果仅针对足跟垫来解释先前发表的体内数据，不仅意味着回弹性能被错误地低估，而且刚度值也低得离谱。
