fitness of entering recruits is not evaluated in advance of basic training and recruits are not required to meet physical fitness standards prior to their transportation (“shipping”) to basic training, the physical training element of basic training is expected to have widely varying effects on recruits. Those who enter basic training with a relatively low level of physical fitness would be expected to find the physical training component of basic training to be more demanding and stressful than those who enter with high physical fitness.

This chapter summarizes the available evidence regarding the relationship between physical fitness and negative outcomes during the first term of military service. Particular focus is given to orthopedic injuries and attrition, both being frequent and very expensive negative outcomes in military recruits. Because military personnel are recruited from the adolescent population, the physical fitness status of contemporary American youth is also reviewed. Our knowledge of the impact of low physical fitness on negative outcomes in military populations is summarized, and the scientific basis of musculoskeletal injuries is briefly presented. Finally, several possible approaches to reducing injuries and attrition in basic trainees are considered. The approaches presented are based on application of the scientific evidence regarding the relationship between physical fitness and injury or attrition in military personnel.

Physical fitness has been verbally and operationally defined in numerous ways. Nonetheless, certain common themes are evident in most of the verbal and operational definitions that have come into wide use over the past century. Most verbal definitions of physical fitness allude to a person’s ability to perform vigorous physical tasks. For example, Clarke defined physical fitness as “the ability to perform daily tasks with vigor and alertness, without undue fatigue, and with ample energy to enjoy leisure pursuits and to meet unforeseen emergencies” (Clarke, 1967). If Clarke’s classic and widely cited definition is applied to first-term military personnel in combat occupational specialties, a soldier who is physically fit would be capable of meeting the considerable physical demands of combat soldiering without experiencing fatigue at a level that unduly limits job performance. In other words, physical fitness is one of the functional capacities of the soldier’s job (see the discussion of functional capacity later in this chapter).

Operational definitions of physical fitness have evolved dramatically over previous decades. However, virtually all accepted operational defi-