Department of Kinesiology, Iowa State University, Ames, IA 50011-1160, USA.
Med Sci Sports Exerc. 2009 Dec;41(12):2177-84. doi: 10.1249/MSS.0b013e3181a984c4.
The fatigue life of bone is inversely related to strain magnitude. Decreasing stride length is a potential mechanism of strain reduction during running. If stride length is decreased, the number of loading cycles will increase for a given mileage. It is unclear if increased loading cycles are detrimental to skeletal health despite reductions in strain.
To determine the effects of stride length and running mileage on the probability of tibial stress fracture.
Ten male subjects ran overground at their preferred running velocity during two conditions: preferred stride length and 10% reduction in preferred stride length. Force platform and kinematic data were collected concurrently. A combination of experimental and musculoskeletal modeling techniques was used to determine joint contact forces acting on the distal tibia. Peak instantaneous joint contact forces served as inputs to a finite element model to estimate tibial strains during stance. Stress fracture probability for stride length conditions and three running mileages (3, 5, and 7 miles x d(-1)) were determined using a probabilistic model of bone damage, repair, and adaptation. Differences in stress fracture probability were compared between conditions using a 2 x 3 repeated-measures ANOVA.
The main effects of stride length (P = 0.017) and running mileage (P = 0.001) were significant. Reducing stride length decreased the probability of stress fracture by 3% to 6%. Increasing running mileage increased the probability of stress fracture by 4% to 10%.
Results suggest that strain magnitude plays a more important role in stress fracture development than the total number of loading cycles. Runners wishing to decrease their probability for tibial stress fracture may benefit from a 10% reduction in stride length.
确定步长和跑步里程对胫骨应力性骨折发生概率的影响。
10 名男性受试者在两种条件下以其喜好的跑步速度在地面上跑步：喜好的步长和喜好步长减少 10%。同时采集力台和运动学数据。实验与肌肉骨骼建模技术的结合用于确定作用于胫骨远端的关节接触力。峰值瞬时关节接触力作为输入输入到有限元模型中，以估计站立时胫骨的应变。使用骨损伤、修复和适应的概率模型来确定步长条件和三种跑步里程（3、5 和 7 英里/天）下的胫骨应力性骨折概率。使用 2×3 重复测量方差分析比较条件之间的骨折概率差异。
步长（P=0.017）和跑步里程（P=0.001）的主要影响显著。减少步长可使骨折概率降低 3%至 6%。增加跑步里程会使骨折概率增加 4%至 10%。
结果表明，应变幅度在应力性骨折发展中比总加载循环数发挥更重要的作用。希望降低胫骨应力性骨折发生概率的跑步者可能会受益于步长减少 10%。
