Fatigue-induced subchondral bone (SCB) injuries are prevalent among athletes due to the repetitive application of high magnitude loads on joints during intense physical training. Existing fatigue studies on bone utilize a standard fatigue test approach by applying loads of a constant magnitude and frequency even though physiological/realistic loading is a combination of various load magnitudes and frequencies. Metal materials in implant and aerospace applications have been studied for fatigue behavior under physiological or realistic loading, however, no such study has been conducted on biological materials like bones. In this study, we investigated fatigue behavior of SCB under the range of loads likely to occur during a fast-workout of an equine athlete in training.

A loading protocol was developed by simulating physiological loads occurring during a fast-workout of a racehorse in training, which consisted of a sequence of compression-compression load cycles, including a warm-up (32, 54, 61 MPa) and cool-down (61, 54, 32 MPa) before and after the slow/fast/slow gallop phase of training, also referred to as a training loop. This loading protocol/training loop was applied at room temperature in load-control mode to cylindrical SCB specimens (n = 12) harvested from third metacarpal medial condyles (MCIII) of twelve thoroughbred racehorses and repeated until fatigue failure. The mean ± standard deviation for total time-to-failure (TTF) was 76,393 ± 64,243 s (equivalent to 18.3 ± 15.7 training workouts) for n = 12 specimens. We observed the highest relative energy loss (REL, hysteresis loss normalized to energy absorbed in a load cycle) under loads equivalent to gallop speeds and all specimens failed under these gallop loads. This demonstrates the importance of the gallop speeds in the development of SCB injury, consistent with observations made in live racehorses. Moreover, specimens with higher mean REL and lower mean stiffness during the first loop had a shorter fatigue life which further confirms the detrimental effect of high energy loss in SCB. Further studies are required to reconcile our results with fatigue injuries among equine athletes and understand the influence of different training programs on the fatigue behavior of subchondral bone.

疲劳引起的软骨下骨（SCB）损伤在运动员中普遍存在，这是由于在剧烈的体育锻炼过程中反复在关节上施加高强度载荷。现有的骨骼疲劳研究采用标准的疲劳测试方法，即通过施加恒定大小和频率的载荷，即使生理/实际载荷是各种载荷大小和频率的组合。已经对植入物和航空航天应用中的金属材料进行了生理或实际载荷下的疲劳行为研究，但是，尚未对诸如骨骼之类的生物材料进行此类研究。在这项研究中，我们调查了马术运动员在训练中快速锻炼过程中可能发生的负荷范围下SCB的疲劳行为。

通过模拟赛马快速锻炼过程中发生的生理负荷来开发负荷方案，该负荷方案包括一系列的压缩-压缩负荷循环，包括预热（32、54、61 MPa）和冷却慢速/快速/慢速疾驰阶段之前和之后的最大压力（61、54、32 MPa），也称为训练循环。在室温下以负载控制模式将这种加载规程/训练环应用于从十二个纯种赛马的第三掌骨内侧con（MCIII）收获的圆柱形SCB标本（n = 12），并重复进行直至疲劳破坏。对于n = 12个样本，总失效时间（TTF）的平均±标准差为76,393±64,243 s（相当于18.3±15.7训练）。我们观察到最高的相对能量损失（REL，磁滞损耗归一化为负载循环中吸收的能量（在等于驰op速度的负载下），并且所有样本在这些驰op负载下均失效。这证明了驰op速度在SCB损伤发展中的重要性，这与在赛马中所做的观察一致。此外，在第一个循环中具有较高平均REL和较低平均刚度的样品的疲劳寿命较短，这进一步证实了SCB中高能量损失的有害影响。需要进一步的研究来使我们的结果与马运动员的疲劳损伤相一致，并了解不同训练计划对软骨下骨疲劳行为的影响。这证明了驰op速度在SCB损伤发展中的重要性，这与在赛马中所做的观察一致。此外，在第一个循环中具有较高平均REL和较低平均刚度的标本具有较短的疲劳寿命，这进一步证实了SCB中高能量损失的有害影响。需要进一步的研究来使我们的结果与马运动员的疲劳损伤相一致，并了解不同训练计划对软骨下骨疲劳行为的影响。这证明了驰op速度在SCB损伤发展中的重要性，这与在赛马中所做的观察一致。此外，在第一个循环中具有较高平均REL和较低平均刚度的标本具有较短的疲劳寿命，这进一步证实了SCB中高能量损失的有害影响。需要进一步的研究来使我们的结果与马运动员的疲劳损伤相一致，并了解不同训练计划对软骨下骨疲劳行为的影响。