Background

Tibial stress fractures in military recruits occur beginning with the fourth week of training. In and ex vivo tibial strain experiments indicate that the repetitive mechanical loading during this time may not alone be sufficient to cause stress fracture. This has led to the hypothesis that the development of tibial stress fracture is mediated by the bone remodeling response to high repetitive strains. This study assesses the differences in the strain and angle of the principal strain during military field activities versus common civilian activities.

Methods

In vivo strain measurements were made from a rosette strain gauge bonded to the midshaft of the medial tibia. Measurements of principal strains and their angles were made while performing level and inclined walking and running on an asphalt surface, while fast walking up and down stairs, while performing a standing vertical jump and while zig-zag running up and down a 30° inclined dirt hill.

Findings

The angle of the principal strain varied little (5.40° to +2.74°) during activities performed on engineered surfaces. During zig-zag running on a dirt hill the strain levels were higher (maximum shear = 4290 με). At the pivot points of zig-zag running the angle of the principal strain varied between −115° to −123° downhill and between −32.8° to −51° uphill.

Interpretation

Activities that mimic those performed by infantry recruits on irregular hilly surfaces result in higher tibial strains and have more variation in principal strain angles than activities of ordinary civilian life performed on engineered surfaces.

中文翻译：

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在自然丘陵地形与工程表面上进行活动期间，主应变角的差异。

背景

从训练的第四周开始，新兵就发生了胫骨应力性骨折。在和离体胫骨应变实验表明，在这段时间内的重复的机械负载可能不单独足以导致应力性骨折。这导致了这样的假设：胫骨应力性骨折的发展是由对高重复性应变的骨骼重塑反应介导的。这项研究评估了军事现场活动与普通民用活动期间主要应变的应变和角度的差异。

方法

体内应变测量是通过结合到胫骨内侧中轴的玫瑰形应变计进行的。测量主应变及其角度时，是在水平和倾斜的柏油路面上行走和奔跑，在楼梯上快速上下走动，站立时是垂直跳跃，而锯齿形则是在倾斜30°的斜坡上奔跑爬坡道。

发现

在工程表面上进行活动时，主应变的角度变化很小（5.40°至+ 2.74°）。在泥土丘上进行之字形行驶期间，应变水平较高（最大剪切力= 4290με）。在之字形运行的枢轴点处，主应变的角度在下坡度-115°至-123°之间以及上坡度-32.8°至-51°之间变化。

解释

模仿步兵新兵在不规则丘陵地表上进行的活动，比在工程表面上进行的普通平民生活的活动产生的胫骨应变更高，主应变角的变化更大。