Traditionally, physical fitness has been emphasized as a critical element in the success of military operations (9,41,44,46) because the occupational tasks that soldiers perform frequently require a high level of physical effort (14,22,24,27,54,55). Physical fitness is increased by physical training of the proper mode, frequency, duration, and intensity (1,38). However, physical training also has its downside: as the amount of physical activity increases, so do injury rates (23,35,36,42,49,57). Injuries can result in physical limitations and disability, which compromise military readiness. A critical goal of military physical training is balancing the need to improve and maintain a high fitness level while minimizing injury risk.
The U.S. Army Physical Fitness School (USAPFS) has responsibility for developing physical training doctrine in the U.S. Army. During the last 7 years, the USAPFS has redesigned Army physical training; this new program is called Physical Readiness Training (PRT). In 2001, USAPFS asked the U.S. Army Center for Health Promotion to evaluate the influence of this new physical training program on injuries and physical fitness. Since that time, PRT has been evaluated in 3 Army environments (Basic Combat Training [BCT], Ordnance Advanced Individual Training [AIT], and an operational infantry unit) and in 1 laboratory study. The purposes of this paper are to 1) provide the rationale for PRT and 2) describe the results of the fitness and injury evaluations of PRT as it was introduced into the military.
Purposes Of Physical Readiness Training
The purposes of PRT are to improve physical fitness, prevent injuries, progressively train soldiers, and develop soldiers' self-confidence and discipline (3).
Physical fitness has been defined in a number of ways (6,7,16,21,43,47,58), but a simple definition that incorporates many aspects of the others is that physical fitness is a set of attributes that allow the performance of physical activity (43). The attributes or components of physical fitness have been determined through factor analytic studies that provide construct validity for the fitness concept (11,34). Fitness components were determined by providing individuals with a broad array of physical performance tests for which quantitative measures could be obtained. Correlational and factor analytic techniques were used to assemble the tests into groups having commonality. After a long series of studies, a number of components were identified, although different authors categorized these components somewhat differently because of the types of tests involved in the different studies (8,11-13,20,45,61). For example, a factor related to cardiovascular endurance could not emerge if there was no long-term endurance activity, which was the case in studies before 1972. Table 1 provides the components of physical fitness and their definitions assembled from a number of sources (7,8,11,16,20,47).
The USAPFS has simplified the components of fitness to strength, endurance, and mobility, in consonance with others (20). Endurance refers to cardiorespiratory endurance, whereas the strength concept incorporates muscular strength, muscular endurance (anaerobic endurance), and power. Mobility is movement proficiency and is considered the skilled application of strength and endurance to occupational tasks. The mobility concept incorporates balance, flexibility, coordination, speed, and agility. Physical fitness improvements in the PRT program are achieved through drills (described later) designed to improve the individual components of fitness.
Another purpose of PRT is to prevent injuries. Injury-prevention measures include reduced running mileage, a greater variety of exercises, and enforced progressive training. A number of studies of runners and individuals in basic military training have shown that longer running mileage is associated with a higher injury incidence (23,35,36,42,49,52). Studies in 3 military services have shown that reducing running mileage can reduce injury incidence without compromising improvements in aerobic fitness (23,52,57). An analysis of these military studies suggests that the total running mileage in the 9-week Army BCT program can be about 25 miles (33), especially in groups of trainees who are in the lower half of the distribution of aerobic fitness levels for recruits first entering military service. Improvements in aerobic fitness are achieved with both interval training and long-distance running. This low running mileage also must be viewed in light of the fact that recruits perform additional occupational running (not part of routine physical training) through obstacle, confidence, and bayonet courses and perform lower-intensity aerobic endeavors such as drill and ceremony, foot marches out to training areas, and other activities. Running distances for each week of basic training and the rationale for these distances have been presented previously (33). Less certain at this point are the running distances that are desirable for soldiers in operational units who have already achieved a baseline level of aerobic fitness.
Another potential injury reduction feature is the variety of exercises in the program. There are no studies indicating that exercise variety will reduce injuries, but sports medicine professionals often endorse “cross-training” for this purpose (56). The cross-training concept simply involves alternating different types of exercises on different days. Exercises are different in the sense that they involve different energy systems (aerobic, anaerobic) or different muscle groups in alternating training sessions. Reducing the repetitive use of energy systems or muscle groups may allow more time for recovery and reduce the probability of overuse injuries.
Progressive training is both an injury-prevention feature and a training feature of PRT. Progressive training involves the prescriptive, gradual introduction of exercise stress to allow steady adaptations to higher levels of physical performance (43). The PRT activities are prescriptive. The training activities, drill repetitions, and running distances are carefully laid out for the trainer in each training session. The PRT activities are gradual because they are introduced slowly and repetitions are increased gradually over multiple training sessions. For example, running mileage in BCT is increased steadily on a measured schedule (33), and the number of speed running repetitions is increased similarly (29). Although the principle of progressive training is endorsed by trainers and exercise physiologists (4,43,60), few studies have tested this principle for its injury reduction potential. One study (51) did attempt to examine a gradual vs. sudden increase in running mileage, but the group involved in the gradual mileage increase also ran fewer miles, confounding the effects of progressive training alone.
Self-Confidence and Discipline
Another purpose of PRT is to develop soldier self-confidence and discipline. Fitness has been shown to be related to self-confidence and self-discipline (19,37). Individuals who maintain fitness tend to be more self-confident, self-disciplined, psychologically resilient, and competitive (19). Discipline also is enhanced by having soldiers exercise in large groups to very precise standards.
Physical Readiness Training Principles
The PRT follows the exercise principles of progressive overload, regularity, and specificity as previously defined (43,48,50,60). Additional principles developed by the USAPFS include precision, variety, and balance (3,48).
Progressive overload is achieved by the prescriptive, gradual training program designed around the U.S. Army military training cycle. This military training cycle takes a civilian and integrates that individual into the military through education and experiences in BCT, AIT, and multiple deployments and redeployments in operational Army units. Individuals entering the U.S. Army begin their careers by completing BCT, in which they acquire basic soldering skills including an introduction to Army physical training. In BCT, PRT involves fundamental and easily performed physical training tasks (e.g., calisthenics, dumbbell drills, climbing drills, running). Progressive overload is accomplished by increasing the number of repetitions of each exercise and by increasing the complexity and difficulty of the exercises (e.g., log drills) as the individual advances from BCT to AIT and into operational military units. In AIT, soldiers learn their military occupational specialty. In operational units, soldiers use the skills and knowledge they have acquired in training and may be assigned to a very wide array of units including infantry, armor, artillery, engineering, aircrew, electronics, communication, health care, administration, mechanical, and craftwork, just to mention a few. In the current environment, overseas deployments and returns from these deployments (redeployments) are facts of military life and must be considered in physical training programs.
Regularity means training frequently and on a set schedule. Regularity is achieved by a physical training doctrine that requires enforced regular physical training at least 3 times per week. Training leaders are encouraged to train the components of physical fitness up to 5 times per week. Training schedules are provided in military publications to achieve this level of training (3,48).
Specificity means training to improve the occupational tasks soldiers perform. Specificity was achieved by attempting to match military tasks (warrior tasks) to specific physical training activities and specific physical fitness components. Military (warrior) tasks are those military activities required of all soldiers (39). Tables 2 and 3 provide examples of how military tasks were matched to fitness components and training activities. Table 2 shows the required military urban operation skills of “movement” and “entry technique,” and Table 3 shows the military task of shooting. Each task has several subtasks. A panel of subject matter experts rated each subtask on a 3-point scale as to the fitness components involved and also determined whether or not a specific PRT activity might improve task performance. Discrepancies were resolved by consensus. Figure 1 is a more dynamic example of how a specific military activity (exiting a vehicle) was linked to a specific physical training activity (the high jumper). Figure 2 provides another example.
Precision, Variety, Balance
Precision involves exact execution of the exercises so that the most beneficial stress can be imparted to the muscles, bones, and joints (5,10,30). Variety (also an injury-prevention measure) is achieved by providing a wide range of training exercises to avoid boredom and to allow for better recovery (56). Balance has a double meaning, ensuring that 1) fitness components are considered to the extent that they are involved in military tasks and 2) antagonistic muscle groups (e.g., hamstrings/quadriceps) are exercised (25,32,59).
Physical Readiness Training Drills
The PRT involves minimal equipment and is designed to be as deployable as the soldier so that the program can be used in any environment in which the soldier operates. The major PRT exercises and drills are shown in Tables 2 and 3 under the columns headed “PRT activities.” The PRT activities were organized into groups of “drills” that involved similar types of movements. The exact exercises involved in each drill are described in a publication (3) and are available online at https://www.infantry.army.mil/usapfs/doctrine.htm. The program can be subdivided further into on-ground tasks (e.g., running, calisthenics, guerrilla drills), off-ground tasks (e.g., climbing drills, conditioning obstacle courses, confidence obstacle courses), and combatives (close, medium, long-range). Combative activities are described in another publication (2).
Some PRT drills are designed to improve a single fitness component, whereas other drills are designed to improve a wider array of fitness components. Examples of drills targeted to a single fitness component are stretching drills designed primarily for flexibility improvement and long-distance and speed running designed primarily to improve cardiorespiratory endurance. Fitness components enhanced by multiple drills include strength, which is improved by dumbbell drills, climbing drills, certain calisthenic exercise (e.g., forward lunges, backward lunges), climbing drills, and certain calisthenic exercises (e.g., push-ups, mountain climber); agility, which is enhanced by shuttle running and certain obstacle course events; and balance and coordination, which are developed by precise execution of calisthenic exercises, by movement drills, and by certain obstacle/confidence course events.
Evaluations Of Physical Readiness Training
There have now been a series of 3 field evaluations that have compared PRT against traditional Army physical training. There is also 1 laboratory investigation that compared PRT against an aerobic and weight training program.
The first evaluation of PRT (31) was conducted during the 9 weeks of BCT. A PRT group (n = 1284) performed calisthenics, dumbbell drills, guerrilla drills, interval training, and long-distance running. A control group (n = 1296) conducted a more traditional physical training program consisting of stretching, calisthenics, sit-up and push-up practice, and ability group running. Injuries were evaluated by examining the medical records of all participants for overuse injuries defined operationally as those presumed to involve repetitive microtrauma (e.g., stress fractures, stress reactions, bursitis, fasciitis, tendonitis). Physical fitness was measured with the Army Physical Fitness Test (APFT), which involves the maximum number of push-ups in 2 minutes, the maximum number of sit-ups in 2 minutes, and a 2-mile run for time. “Passing” criteria for the APFT are age- and gender adjusted (48). Both groups had a total of 34 physical training sessions. At the end of the 9-week BCT cycle and after adjusting for covariates known to influence injuries, men in the control group had an injury risk 1.5 times higher (95% confidence interval [CI] = 1.0-2.1) than men in the PRT group; women in the control group had an injury risk 1.4 times higher (95% CI = 1.1-1.8) than women in the PRT group. There were no differences between the PRT and control group in the proportion of trainees passing the initial APFT given at the start of training; however, on the final APFT, the PRT group had a higher pass rate than the control group (83 vs. 75%, p < 0.01).
Thus, on the first investigation injury risk was lower and APFT scores were higher in the PRT group. However, the Army leadership expressed some concern over the cost and logistics associated with some of the drills and desired a second investigation to verify the results of the first. The PRT program was modified based on lessons learned in the first investigation, input from the military leadership, and feedback from the trainers. In another study (29), a PRT group (n = 829) was compared with a control group (n = 1138) that implemented a traditional BCT physical training program that was similar to the program in the previous BCT study. This time, injury data were obtained from a medical surveillance system that collected injuries as ICD-9 codes and specific codes were used to define injuries (28). After adjusting for covariates known to influence injuries, men in the control group had an injury risk 1.6 times greater (95% CI = 1.2-2.0) than men in the PRT group; women in the control group had an injury risk 1.5 times greater (95% CI = 1.2-1.8) than women in the PRT group. There were no group differences in the proportion of trainees passing the initial APFT, but, on the final APFT, pass rates were higher for the PRT group (84 vs. 88%, p = 0.02). Thus, the results of this investigation generally confirm the first BCT evaluation.
Another investigation was conducted in an Ordnance AIT unit (26). A historical control group (n = 2259) was compared with an intervention group (n = 1283). The intervention group conducted the PRT program, and the historical control group performed a traditional Army physical training program consisting of stretching, calisthenics, push-up/sit-up exercises, and running. Trainers in the intervention group were also given a special injury-prevention training course, were provided with weekly injury rates, and participated in an injury advisory committee that met on a monthly basis to discuss injury problems. At the completion of the 9-month intervention period, and after adjusting for known injury risk factors, men in the control group had an injury risk 1.5 times greater (95% CI = 1.2-1.8) than men in the PRT group; women in the control group had an injury risk 1.8 times greater (95% CI = 1.1-2.8) than women in the PRT group. On the final APFT, pass rates were not different between the PRT and control groups (80 vs. 82%, respectively; p = 0.17).
Most recently, PRT was evaluated in an infantry unit preparing for deployment to Afghanistan. In this evaluation, a battalion of male soldiers (n = 477) using the PRT program was compared with a battalion of male soldiers using a traditional but highly varied physical training program (n = 467). At the end of the 9-week evaluation, systematic medical records screening indicated that control group soldiers were 1.2 (95% CI = 0.9-1.7) times more likely to suffer an overuse injury and 1.4 (95% CI = 1.0-2.0) times more likely to experience a lower-extremity overuse injury. Fitness differences were not evaluated.
It should be noted that all of these evaluations were conducted while PRT was being phased into Army physical training. The PRT groups were those that were trained on the new techniques early during the phase-in process, whereas control groups were those that were required to phase in PRT later but were using traditional training at the time of the evaluations. Thus, subjects were not randomized into groups. Further, the Ordnance School evaluation involved a multiple intervention program that included injury-prevention education for the training cadre, a weekly injury report, and a monthly injury-prevention meeting, besides the training program. Despite these potential confounders, all 4 studies were consistent in showing that injury rates were lower or tended to be lower in the PRT program when compared with traditional Army physical training programs. The 2 basic training studies (29,31) indicated that APFT pass rates were higher in the PRT group, but there were no group fitness differences in the Ordnance AIT evaluation (26), and fitness differences were not assessed in the infantry evaluation.
A laboratory study (15,17,18) compared a group using PRT (n = 17) with a group performing weight training, running, interval training, agility drills, and progressively loaded hikes (n = 15). The programs were conducted for 8 weeks, 5 d·wk−1, for 1.5 h·d−1. Pre- and posttest measures were designed to simulate occupational military tasks and included 1) a 3.2-km run with a 32-kg backpack load, 2) a 400-m run with an 18-kg backpack load, 3) an obstacle course, 4) 5 × 30-m rushes to and from the prone position, 5) an 80-kg casualty drag across 50 m, 6) a standing vertical jump, 7) a standing horizontal jump, and 8) a 3.2-km unloaded run. Additional pre-post measures included a treadmill o2max and body composition assessment using dual-energy X-ray absorptiometry (DEXA). Both groups improved significantly on all simulated occupational military tasks, and improvements did not differ between groups except on the obstacle course, on which the PRT group's performance improvement was significantly greater (16 vs. 10%). The o2max and DEXA body composition changes were not different between groups. Thus, similar improvements were obtained with both programs despite considerably less equipment involvement with the PRT program.
Developing efforts in PRT focus on further increasing the fitness of soldiers once they reach their operational units and how to cycle or periodize physical training in light of the frequent deployments in which soldiers now participate. Emerging research has demonstrated that losses in fitness are much less than expected in some types of deployments. It was shown that body composition and strength changed little after deployments to Afghanistan or Iraq, but there was some consistent, although minor, loss of aerobic fitness. The smaller-than-expected fitness losses may be associated with soldiers using PRT while on deployment or the fact that, on deployments, soldiers often operate out of fixed facilities and have access to exercise equipment (40,53).
The PRT follows specific physical training principles and is designed to improve military occupational tasks through the matching of military tasks with specific physical training exercises designed to improve specific fitness components. When compared with traditional Army physical training programs, injury rates are lower and fitness improvements are generally equal or higher in PRT programs. The PRT will continue to be developed and refined based on deployment research, feedback from trainers, commanders, and soldiers in the field and as common soldiering tasks are updated or changed to meet national security requirements.
The views, opinions, and/or findings contained in this report are those of the authors and should not be construed as official Department of the Army positions, policies, or decisions, unless so designated by other official documentation. Approved for public release; distribution is unlimited.
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