In vitro real-time replication of three-dimensional, time-varying load profiles acting on human bones during physical activity can advance bone and implant testing protocols. This study aimed to develop a novel protocol for applying the three-dimensional, time-varying hip contact force while walking to a human femur specimen. The target force profile was obtained from the literature. A proximal femur from an elderly female donor was instrumented using ten rosette strain gages and tested using a custom-made hexapod robot. A load-control algorithm determined the robot position generating the target force at low frequency (0.0004 Hz). Five cycles of the robot position were played back at five intermediate frequencies up to real-time (0.04, 0.08, 0.16, 0.4, and 0.8 Hz). The hip reaction force, the length of the actuators (position), and cortical strains were compared. The error in the load-control force was 0.3 ± 4.2 N (mean ± SD). The last three force, position, and strain cycles varied by less than 1.1% for every frequency analyzed. Across frequencies, the force increased by 28% at 0.8 Hz as a logarithmic function of frequency (R² = 0.98). The position and strain error linearly increased with frequency up to 0.4 Hz. The median position error and the interquartile range of the strain error reached 15% and 13% at 0.8 Hz. Changes of force and cortical strain at increasing frequencies were linearly related (R² = 0.99). Therefore, the protocol developed can provide repeatable three-dimensional time-varying load profiles, although the comparison of the specimen deformation obtained across frequencies should be considered with care, particularly in the higher frequency range. This information supports the design of dynamic tests of bone and implants.

在体力活动期间作用于人体骨骼的 3 维、时变负载曲线的体外实时复制可以推进骨骼和植入物测试协议。本研究旨在开发一种新方案，用于在步行到人类股骨标本时应用三维、时变的髋关节接触力。目标力分布是从文献中获得的。一位老年女性捐献者的股骨近端使用 10 个玫瑰花应变计进行检测，并使用定制的六足机器人进行测试。负载控制算法确定了在低频 (0.0004 Hz) 下产生目标力的机器人位置。机器人位置的五个周期以五个中频实时回放（0.04、0.08、0.16、0.4 和 0.8 Hz）。髋部反作用力，执行器的长度（位置），和皮质菌株进行了比较。负载控制力的误差为 0.3 ± 4.2 N（平均值 ± SD）。对于分析的每个频率，最后三个力、位置和应变循环的变化小于 1.1%。在频率范围内，力在 0.8 Hz 时增加了 28%，作为频率的对数函数 (R²  = 0.98）。位置和应变误差随频率线性增加至 0.4 Hz。在 0.8 Hz 时，中位位置误差和应变误差的四分位距分别达到 15% 和 13%。随着频率的增加，力和皮质应变的变化呈线性相关（R ²  = 0.99）。因此, 开发的协议可以提供可重复的三维时变载荷剖面, 尽管应谨慎考虑跨频率获得的试样变形的比较, 特别是在较高的频率范围内。此信息支持骨骼和植入物的动态测试设计。