Before 1978, women serving in the U.S. Army were segregated from men into the Women's Army Corps (WAC). That year marked the official disbanding of the WAC, and thus women began integrating with men during basic combat training (BCT) and noncombat military occupational specialties (MOSs). This historic decision to end segregated training required the U.S. Army to evaluate women's physiological responses to the physical demands of military training. As of 2013, the 1994 Direct Ground Combat Definition and Assignment Rule excluding women from serving in direct combat roles was rescinded, resulting in the availability of over 14,000 military jobs that were previously closed to women (6). Because women integrate into combat MOSs, the physiological demand placed on them during military skills training and occupational tasks will be greater than the physical requirements of noncombat MOSs. The ability to lift and carry loads, often for extended durations, is a recurrent physical demand in hostile and austere environments. The evolution of modern warfare has brought about an increase in external loads requiring soldiers to carry more weight (40). This occupational demand may be a contributing factor in the exponential increases in musculoskeletal injuries (35,36). Therefore, there is an emerging need for strength and conditioning professionals to prescribe and manage physical training (PT) programs that will meet the challenges within these military roles. This article will discuss peer-reviewed research regarding the importance of a periodized training program for female soldiers, the physical response to various exercise stimuli and military movements, and suggest training strategies to improve physical and military performance.
Currently, women comprise approximately 15% of the U.S. military, 13.6% of the active Army, and serve in 95% of all occupational specialties (5,22). Most of these MOSs can be physically arduous, especially combat MOSs, requiring individuals to perform occupational tasks that involve lifting, carrying, climbing, throwing, crawling, and load bearing (≥40 kg) at a moment's notice (see Video, Supplemental Digital Content 1, http://links.lww.com/SCJ/A137, which demonstrates combat MOS tasks) (18,23). The physical demands of these tasks use both anaerobic and aerobic energy systems. Considering the fitness levels of both men and women, research suggests that women may have baseline strength levels that are lower than that of most men, underscoring the necessity to develop training programs that address physical limitations and meet the current needs of the military (16,18).
The Army is currently conducting an evaluation of combat MOS tasks (e.g., load carriage over long distances, sprinting short distances to overtake a hostile position, carrying personnel to safety, and repetitive lifting of heavy objects), which will provide insight into the physiological demands of each occupation and help shape the design of the PT program. A previous examination of military occupational tasks of a light infantry unit revealed that the majority of tasks require moderate-to-high outputs of muscular strength, muscular endurance, and mobility (26). Currently, soldiers in these types of units will conduct tactical movements carrying an “approach” load averaging 46 kg for 6–8 km patrols twice a day in a combat environment. These tasks place a high physiological demand on the cardiovascular system. Additionally, other tasks require a high level of muscular strength. For example, dragging a 123-kg casualty to safety or moving pieces of a bailey bridge weighing 94 kg for 50 m (Figure 1).
Traditionally, military PT conducted at the unit level overemphasized aerobic exercise and muscle endurance and typically lacked strength, agility, and power training—components of fitness that correlate well with the physical demand requirements of many occupational tasks (e.g., repetitive box lifting, climbing, and carrying loads). The lack of adequate strength and power training as part of a PT program may result in injury and lost training days because soldiers attempt to perform high-intensity occupational tasks that they are physically unprepared to perform. Understandably, injuries not only lead to a loss of training days but also lead to increases in costs from clinical encounters and personnel shortages (9,30,41).
Injury reduction seems to be optimally managed using a concurrent aerobic and resistance training program that includes a dynamic warm-up and cool down. Without the correct exercise prescription, the risk of injury is increased as a result of physical unpreparedness when attempting to meet the physical demands of military occupations. Previous studies have reported that low levels of fitness and slower 2-mile run times are associated with greater risk of injury (12,14,17). For women, having the fitness capacity to sustain a high-intensity workload is important. In a study by Knapik et al., (17), it was reported that women had over twice the injury rate for all injuries, likely because of the high relative intensity of the physical activities encountered during BCT. Evidence suggests that improving physical work capacity through the integration of a properly periodized strength and power training program concurrent with aerobic and endurance training will positively influence injury reduction (20,25).
The implementation of injury reduction strategies are important considerations for an effective PT program. Exercise modalities that improve bone mineral density (BMD) and thus reduce the likelihood for stress fractures should be used (21). Stress fractures among female soldiers can be problematic for military service and occur at a higher rate in females compared with males entering the military (4). Evidence suggests that resistance training may be an effective stress fracture reduction measure when prescribed appropriately. Several studies have examined the effects of resistance training on BMD, and the results are encouraging. For example, 8 weeks of PT that includes a combination of aerobic and resistance training results in changes in bone biomarkers indicative of increased bone formation, an important consideration when developing PT programs for women (7,8,21).
During the performance of job tasks, military personnel are often required to safely execute quick, explosive, and repetitive movements, as well as be able to carry heavy loads, all of which can be vital physical attributes associated with combat survival. Adding an agility training component to the PT program will ensure that female soldiers strengthen the neuromuscular movement motor patterns that will both improve performance and also mitigate injury (2,3,25,27,31).
Soldiers often endure physically demanding work environments; therefore, superimposing intense PT sessions onto daily occupational demands has the potential to result in unplanned overreaching and overtraining. Although heavy resistance training, agility training, and high-intensity training positively influence injury reduction, body composition, and fitness when prescribed appropriately (18,24,28,38), female soldiers may respond differently to such training (18,39). This may require longer recovery periods between bouts of intense exercise, modified PT workouts, or both to prevent overtraining and injury. It is up to the strength and conditioning specialist to ensure that the PT program takes into account all facets of the soldier's demands of daily living to ensure that adequate recovery and progression occur and to ensure that injury and overtraining are minimized.
Progression and specificity are key factors to the success of any fitness program. A gradual introduction of exercise stress allows steady adaptation to higher levels of physical performance. Traversing rough terrain and obstacles, both in urban and mountainous environments, are current environmental barriers that a soldier must negotiate. Therefore, progressively introducing training modalities that improve balance, proprioception, and agility should be considered and can easily be integrated into the dynamic warm-up portion of the workout (20).
Performing repetitive lifts, carrying equipment and ammunition, wearing a “fighting” load (≥29 kg), and climbing over around and through obstacles require soldiers to maintain their muscular strength and endurance. Multijoint lifts, such as squats, pull-ups, deadlifts, rows, and so on, must be part of a routine developed to maximize physical preparedness. Workout days should alternate from high intensity (>85% repetition maximum [1RM]) to lower intensity (<67% 1RM) throughout a week to meet these demands. The repetitions and sets should correspond to the intensity level (Table 1). Distance running, sprinting, and hill repeats should also be included throughout training to maintain aerobic capacity. General strength exercises and multijoint lifts should be performed before specific single-joint exercises.
Several studies have shown that conditioning programs consisting of resistance and cardiovascular training in female soldiers improve physical performance, including adaptations in strength, power, and endurance, and also show that resistance training reduces gender differences in physical performance (10,15,18,19,31). Kraemer et al. (18) examined several periodized resistance training programs over a 6-month period. Subjects in the study were grouped into a total or upper-body only strength/power exercise program using 3- to 8-RM loads, a total or upper-body only strength/hypertrophy exercise program using 8- to 12-RM loads, an aerobic-only group, and a field exercise group. The field exercise group was limited to body weight, partner-assisted resistance, and ballistic exercise. The results of the study demonstrated that improvements were specific to the type of training program used. Significant improvements were observed in military occupational tasks such as repetitive box lifting in both the total body and upper-body resistance training groups. The study also demonstrated improvements in 1RM squat and bench press in the field training group during the first 3 months of training, supporting the inclusion of alternate training methods into a strength training program when traditional resistance training equipment may not be available. Most importantly, because it relates to the disparity of strength between men and women, this study demonstrated that 6 months of resistance training reduced the gender gap in physical performance measures. Moreover, all female soldiers in the resistance training groups successfully attained scores in the 2-minute push-up, 2-minute sit-up, and 2-mile run events that would pass the Army Physical Fitness Test (APFT), whereas the same was not true in the aerobic or field exercise groups. To support the importance of resistance training as an effective strategy to improve the ability to perform occupational tasks, Knapik (16) also reported that progressive resistance exercise with interval training improved the manual material handling capability of female soldiers. Additional studies support a combination of various types of training that include strength, power, ballistic, and plyometric exercises to elicit the greatest performance improvements in women (11,13,29,37).
When monitoring the strength and conditioning program, it can be expected that men and women may exhibit different responses to the program, especially in new trainees. Kell (15) examined the absolute and relative strength of men and women with previous resistance training experience after a 12-week traditionally periodized resistance training program. The program was a split routine with intensity of 55–87% for 3–4 sets per exercise. An approximate 28–38% increase in strength was seen in both female and male soldiers as a result of the periodized resistance training. Although the men were stronger in absolute terms, the women were more responsive to the training program.
The APFT is comprised a 2-mile run and 2 minutes of push-ups and sit-ups. Desired outcomes of an Army PT program should not only be based on measurable improvements in the performance of the APFT events. By military standards, physical improvements should include decreased run/loaded march times for a specific distance and increasing the number of push-up and sit-up repetitions in a given time. Improving performance safely and effectively with considerations of daily mission requirements and operational tempo are necessary metrics by which to monitor workouts, performance, rest, and recovery. Resistance training provides a stimulus by which women can significantly improve strength, and thus increase the likelihood of safely and successfully performing military occupational tasks that require a strength component.
The use of a periodized resistance training program allows for planned variation in the exercise stimuli through changes in volume and intensity (1,19,20,32–34). The 2 major models of periodization are linear and undulating (nonlinear). Linear periodization is a classic model that uses gradual increases in the training intensity while decreasing the training volume between cycles. Undulating periodization has more frequent adjustments in the intensity and volume, thus providing greater demands on the neuromuscular system and continuous changes on the stimuli (33).
An undulating periodization program can be modified based on the acute demands of the mission that may warrant rest/recovery. Increased awareness of lifting and movement technique coupled with neuromuscular adaptations may result in better task performance, reduced plateau in training, and a decrease in musculoskeletal injuries (33,40). Soldiers need to vary their daily intensity and volume to maximize strength increases and avoid stagnation. Particularly important is the ability to track unit training that may affect or be affected by PT. Many Army units have training cycles that can be physically and psychologically demanding. This information will be useful because the periodization scheme of the PT program is developed along with an understanding that acute amendments to the PT schedule may be warranted based on feedback and the daily physical status of soldiers (e.g., delayed onset muscle soreness, illness, fatigue, and so on).
Occupational demands (e.g., load carriage, box lifting) often require multijoint functioning, and several studies have examined long-term effects of multijoint exercises on the physical performance in women. Kraemer et al. (18,19) showed that a nonlinear program focused on strength and power using multijoint exercises was capable of producing continued increases in muscle hypertrophy in untrained women beyond 6 months. In another study, Reynolds et al. (31) conducted a 24-week periodized strength- and running-based training program in 45 recreationally active women, which resulted in a 33% improvement in maximum box weight that was lifted to a height of 52 inches. When posttraining results were compared with a sample of Army men, the women's average maximum box weight lifted was 81% (117 lb) of the box weight lifted by men (144 lb). Additionally, the study found that the women's loaded marching speed was 80% (4 mph) of the men's speed (5 mph) after completion of the training program. Although female soldiers were not able to lift as much weight as their male counterparts, the average weight lifted by women at the conclusion of this study falls within the MOS Physical Demands Rating of “heavy” by the U.S. Army. This study further supports that a periodized exercise training program results in significant performance improvements in women, thus narrowing the margin of fitness outcomes between men and women (Figure 2).
Competitive athletes generally tailor their PT to a specific sport and position and periodize their exercise training so that they are at their peak physical performance during a competitive season or event. Soldiers, however, must possess a strong foundation of fitness consisting of a myriad of physical capabilities that draw on all facets of physical and psychological fitness necessary to successfully maintain a state of physical and operational readiness. Considering that women are integrating into broader military occupational roles that are often physically arduous and conducted in hostile and austere environments, appropriate PT is the conduit to unit physical and operational readiness.
As the PT program is developed, the unique set of skills and physical capabilities (e.g., baseline fitness measures, military task requirements, and rate of physical progression) of all soldiers in a unit need to be assessed, along with an understanding that acute or daily adjustments may be needed based on operational tempo and soldier feedback. Additionally, disparities exist between men and women in baseline fitness measures of power, muscular strength, and endurance, which are important considerations when developing and implementing a PT program. A concurrent PT program consisting of both cardiovascular and resistance exercises that physically tax all muscle groups and develops all fitness parameters is a requisite to successfully perform military occupational tasks and mitigate injuries. Additionally, an undulating periodized fitness program will optimally prepare the female soldier for future endeavors that require a high level of physical preparedness while also reducing the potential for injury. It is the responsibility of the strength and conditioning professional to design PT programs that increase the physical work capacity of women by enabling them to attain their maximal physiological potential.
The authors would like to thank Dr Edward J. Zambraski, Dr Jan E. Redmond, Marilyn Sharp, and Kristen Heavens for their valuable input and guidance in the development of this article.
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