men and between 17 and 62 percent for women (Almeida et al., 1999; Cowan et al., 1996; Jones et al., 1993a, 1993b; Kaufman et al., 1999; Knapik et al., 1993; Kowal, 1980; Reinker and Ozburne, 1979; Reynolds et al., 1994; Shaffer et al., 1999b). In studies that reported injury rates for both male and female recruits, the injury rate for women was twice as high as the injury rate for men.

A number of previous studies have established a range of risk factors for injury during military training. Recent reviews of risk factors for training-related injuries (Jones and Knapik, 1999; Kaufman, Brodine, and Shaffer, 2000) identified a range of risk factors for injury in the military, including low levels of physical fitness (Shaffer, 1999a; Jones et al., 1993a; Knapik et al., 1993), high and low flexibility (Knapik et al., 1993), anatomical factors (Kaufman et al., 1999), and smoking (Reynolds et al., 1994).

As noted throughout this volume, attrition is a substantial problem among first-term military enlistees. However, the degree to which the problem is attributed directly to musculoskeletal injuries is less clear. A Government Accounting Office report has stated that the Department of Defense lacks consistent and complete information on the causes of attrition (U.S. Senate Committee on Armed Services, Subcommittee on Personnel, 1997). According to this report, a significant portion of first-term attrition occurs during the first six months in the service. For instance, in 1994, 6-month attrition rates were 15.7 percent for the Army, 15.7 percent for the Navy, 12.5 percent for the Marine Corps, and 11.6 percent for the Air Force. This means that, in one year, more than 25,000 new recruits did not remain in the military beyond the training phase.

Poor Physical Fitness as a Risk Factor for Injury and Attrition

Injury

Research on the relationship between physical fitness and training injuries in men and women has been conducted by several researchers (Jones, 1992; Jones et al., 1993a; Westphal et al., 1996). These studies found that individuals with faster performance on a timed run (more aerobically fit) suffered significantly fewer injuries than slow runners. For men, 36 percent of the fast runners and 61 percent of the slow runners reported musculoskeletal injuries (Jones, 1992); for women, 50 percent of the fast runners and 71 percent of the slow runners reported injuries (Westphal et al., 1996). More recent research suggests that the effect of cardiorespiratory fitness may possibly interact with BMI, with leaner, slower recruits tending to have the highest risk of injury (Jones, Darakjy, and Knapik, 2004).

To model the effect of low cardiorespiratory fitness on injury and attrition, the committee used data provided by the U.S. Army Center for



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