Stress fractures in female soldiers: An epidemiological investigation of an outbreak

Abstract

Stress fractures present an important problem to military recruits of both sexes. Among the risk factors for their development are non-gradual exercise, the carrying of heavy equipment, training on asphalt roads, ill-fitting shoes, bony abnormalities of the feet, and excessive fatigue. In a military base involved in basic and advanced training programs for female soldiers, a substantial rise in the incidence of stress fractures occurred in the advanced course during the winter of 1986 (11.4% of the participants as compared to 1.5 to 3% in many previous courses). To study the causes of the outbreak, a comparison was made between the course under discussion and the previous ones regarding the population involved and the training program. The soldiers with stress fractures were compared to their healthy companions as to factors known to influence the incidence of stress fractures. We found that in the index course a change had been made in the training program in that the first hike was performed in a different area. Although the length of the hike remained unchanged, walking was considerably more difficult due to the rocky terrain and steep slopes. The second hike was performed at a much faster pace than usual. During the third week of the course, soldiers were allowed only three to four hours of sleep each night, as contrasted with six hours in other weeks and in previous courses. Most stress fractures revealed themselves during that week and the following one. Two thirds of the fractures were in the tibia and the rest were femoral. Soldiers with stress fractures tended to be heavier, but the difference did not reach significance. Our work emphasizes the importance of road conditions for hikes and of sufficient night sleep in the initial training period. Gradual exercise, comfortable road conditions, and at least six hours of night sleep may reduce the incidence of stress fractures in female military recruits. The applicability of these conclusions to other populations should be separately examined.