Physical fitness has been identified as crucial for military performance (10,27) and injury prevention in military organizations (12,16,22). Recruits require a high level of aerobic endurance and muscular strength to be able to perform their jobs effectively (10,27). Because the physical fitness of young men in the Norwegian, Finnish, and Swiss Armies has decreased over the last 20 years (4,24,31), more and more conscripts are physically ill prepared for military service. Because the physical demands of military service are high (14–18 MJ·d−1 total energy expenditure [29,30]), a low level of physical fitness is one of the most relevant risk factors for injuries (12,13,22). Therefore, it is in the best interest of every military organization to enhance their recruits' individual physical fitness during basic military training.
Miller et al. (19) defined physical fitness as a state of ability to perform sustained physical work characterized by an effective integration of cardiorespiratory endurance, strength, flexibility, coordination, and body composition. To develop all those components, regular and diversified physical training is needed. According to the recommendations of the American College of Sports Medicine (1), a well-rounded training program should include aerobic and strength training for the major muscle groups. A frequency of 3–5 and 2–3 training sessions per week is recommended for the improvement of aerobic fitness and muscular strength, respectively. When those recommendations have been met, improvements in task performance in military settings have been observed in as little as 4–8 weeks (7,8,26).
The Swiss Army regulations specify 2 physical training sessions per week with a total duration of at least 3 hours. These training sessions include aerobic and strength fitness training, team sports, obstacle courses, physical fitness tests, and orienteering. However, recruits' experiences and experts' appraisals indicate that in most of the Swiss Army military training schools, the physical training sessions are not implemented as prescribed, in terms of frequency, duration, and content. Responsible officers cite limited infrastructure and time for physical training in the education program and personnel shortages as reasons for the gap between prescribed and actual training. The recommendations of the American College of Sports Medicine (1) concerning a frequency of at least 3 weekly training sessions are not being fulfilled in the Swiss Army. Therefore, an additional weekly outdoor circuit training program, implemented as part of basic military training, was evaluated as a possibility to increase the number of physical training sessions in a restrictive setting such as the Swiss Army. The impact of this additional weekly physical training session on physical fitness and injury incidence rate was analyzed.
Experimental Approach to the Problem
An intervention group and a control group based at the Fusilier Infantry Training School in Neuchlen, Switzerland, were compared. The study groups were investigated during 2 consecutive military training school cycles: The control group was assessed in the first cycle with the basic military training starting in the summer of 2009, the intervention group in the second cycle starting in spring 2010. Recruits passed no specific pretraining. The control group performed the standard physical training only. The intervention group participated in one additional weekly outdoor circuit training session, apart from the standard physical training, during the 7-week basic military training.
The main outcomes investigated were physical fitness values and injury incidence rates. Physical fitness was assessed in the first and last weeks of basic training (7 weeks). Every volunteer was measured both times on the same weekday and at the same time. Injury data for the entire 21 weeks of military training school were collected and examined.
A total of 435 male recruits from the Fusilier Infantry Training School in Neuchlen, Switzerland, volunteered to participate. Of the 435 volunteers, 100 randomly chosen individuals (50 per study group) wore uniaxial accelerometers (GT1M, ActiGraph LLC, Fort Walton Beach, FL, USA) and a Suunto Smart Belt (Suunto, Vantaa, Finland) heart rate monitor for the assessment of daily physical activities. All the volunteers were given detailed information about the design of the study with a clear description of possible risks and discomforts that might occur. Subsequently, they signed an informed consent form before the experiment. This study was conducted according to the Swiss Law (Therapeutic Product Acts HMG, Bern 2000) and was approved by the Ethical Committees of Cantons Bern and St. Gallen, Switzerland. Of all volunteers, 122 (28.0%) did not participate in the second physical fitness test, and for 54 (12.4%), no medical records were available after military service. Finally, complete physical fitness and injury data of 259 (59.5%) volunteers (age, 20.69 ± 1.17 years; weight, 73.69 ± 9.56 kg; height, 1.78 ± 0.07 m; body mass index, 23.29 ± 2.55 kg·m−2) were recorded and used for analyses in this study (Table 1).
Both study groups performed the standard physical training program according to the Swiss Army's regulations. The standard training program is specified to consist of 2 physical training sessions with a total duration of at least 3 h·wk−1. It is normally guided by one physical training instructor per group of 20–50 recruits. The standard physical training is performed in a gymnasium hall or outdoors, depending on the content of the main part of the training session. Further, because it is performed in large groups, only marginal individual adaptations of intensity are allowed.
Each standard training session is regulated to include 15 minutes of cardiovascular warm-up exercises and dynamic stretching in the beginning and 15 minutes of cooldown activities such as static stretching at the end of the session. The main component changes with every training session and consists of 60 minutes of strength and aerobic fitness training (endurance run in group or circuit calisthenics training in a gymnasium hall, 5 sessions in 7 weeks), team sports (content by choice of recruits, 3 sessions in 7 weeks), obstacle courses (3 sessions in 7 weeks), physical fitness tests (twice in 7 weeks), or orienteering (once in 7 weeks). The physical training instructor chooses the order of those training sessions based on available infrastructure and actual weather.
The intervention group participated in an additional weekly outdoor circuit training program. This additional training session of about 60 minutes was performed in groups of not >10 recruits per circuit exercise station in a circuit calisthenics and aerobic fitness training format. One physical training instructor was allowed to supervise up to 70 recruits performing their circuit training at the same time. It was performed outdoors on an approximately 1-km course. At every circuit exercise station, a waterproof poster with illustrated information was installed. No additional material or gymnasium hall was needed. In the first week of basic military training, a physical education teacher instructed recruits on how to perform the specific training exercises, the number of repetitions or intensity per exercise, according to the individuals' initial physical fitness level. The outdoor circuit training program included warm-up exercises (joint mobility exercises for the whole body and slow running; 10 minutes overall), calisthenics for muscular fitness (squats, prone bridge, back and shoulder exercise, stair climbing, side bridge; 3 × 1 minute each), exercises for postural control (single leg balance stand, walking on a balance beam; 3 × 1 minute each), intermittent episodes of aerobic fitness (running; 3 × 3 minutes each), and an active recovery period (static stretching and slow running; 20 minutes overall).
A standardized protocol was used in both study groups to assess content, duration, and frequency of standard training and outdoor circuit training. Physical training instructors (military personnel with specific education as military sports instructors) recorded information about the content and duration of the training sessions immediately after each session.
Anthropometry and Physical Fitness
Body weight and height data were collected during the first week of basic military training with a portable stadiometer (Seca model 214, Seca GmbH, Hamburg, Germany) and a calibrated scale (Seca model 877, Seca GmbH). Body mass index was calculated as weight·height−2 (kilograms per square meter).
Volunteers' physical fitness was assessed during the first and last weeks of basic military training (7 weeks) using the Swiss physical fitness test battery (SPFT ). The SPFT consists of a standing long jump (SLJ) and a seated 2-kg shot put (SSP) to measure muscle power of lower and upper extremities, respectively, a 1-leg standing test (OLS) to measure postural control, a trunk muscle strength test (TMS, also referred to as prone bridge) to measure trunk muscle fitness, and a progressive endurance run (PER) to measure aerobic fitness. The SLJ was performed from the gymnasium hall floor onto a thin mat, measuring the distance from the scratch line to the closest point of body contact on the landing mat. For the SSP, the subjects sat upright on a bench and their backs were in constant contact with a vertical wall while performing the chest pass of a 2-kg medicine ball. The distance between wall and landing point was measured. The participants performing OLS stood on 1 leg. After 10 seconds, they had to close their eyes and tilt their head backwards after 20 seconds in position. The time of the correct position was measured for the left and right legs separately, and the sum of both was used to evaluate balance ability. In TMS, the volunteers had to hold an isometric body position (prone bridge, on forearms and feet with the upper body and legs in a straight line) for as long as possible while lifting their feet alternately at 1 Hz. The PER was conducted according to the protocol developed by Conconi et al. (2), and the final running velocity was analyzed. The results of all the tests were transformed into an overall score (range: 0–125 points). Precise descriptions of the SPFT, test-retest reliability values (r = 0.77–0.90, p < 0.05), concurrent validity values (r = 0.65–0.91, p < 0.05), and standard values for men of 19.9 ± 1.0 years (n = 12,862) have been published previously for each single test (33).
Daily Physical Activities
Physical activity energy expenditure (PAEE) and distance covered on foot were assessed in the second, fourth, sixth, and eighth weeks of military service. Uniaxial accelerometers were used to monitor recruits' hip acceleration in the vertical direction and step frequency. Suunto Smart Belts were used to record recruits' heart rate. Accelerometer and heart rate data were synchronized by a self-programmed application using Matlab (Matlab 5.3, MathWorks, Natick, MA, USA). To estimate PAEE based on this sensor data, algorithms by Wyss et al. (32) were used. For each investigated day of basic military training, the median of volunteers' distance covered on foot and PAEE were calculated. Daily results were then used to calculate average values per week for both study groups.
Injuries were registered when an individual visited the medical care center for injury reasons. Injury data of volunteers were continuously collected in their medical records by the medical staff during the 21 weeks of military training school. The injury incidence rate was expressed as the total number of injuries per month per 100 recruits. Overuse injuries were defined as those associated with repetitive physical activities and those that occurred without any specific traumatic event.
All statistical analyses were conducted using SPSS for Windows (version 16.0, SPSS Inc., Chicago, IL, USA). The accepted level of significance was set at p < 0.05 for all analyses. Data were expressed as means ± SD. Independent samples t-tests were conducted to compare the 2 study groups in terms of (a) volunteers' age and anthropometric data, (b) average distance covered on foot and PAEE, and (c) physical fitness in first and last weeks of basic military training (7 weeks). Wilcoxon rank-sum tests were conducted to compare the 2 study groups in terms of frequency of the 5 classes of content for standard trainings during 7-week basic military training. Paired samples t-tests were conducted to analyze the changes in physical fitness for each study group. For further investigation, the volunteers in both study groups were subdivided into tertiles according to their initial physical fitness level (third of subjects with lowest, medium, and highest fitness level). Paired samples t-tests were conducted to analyze the changes in physical fitness for the third of subjects with the lowest and the third of subjects with the highest initial physical fitness level. Pearson's chi-square tests were used to analyze the differences in injury incidence rate (overall and overuse injuries) between the intervention and control groups and between the third of subjects with the lowest and the third of subjects with the highest initial physical fitness level within each study group. Descriptive statistics were used to describe frequency, duration, and content of physical training in both study groups.
The sample size for the independent samples t-tests was calculated according to the spreadsheet provided by Soper (28). This calculation was based on an alpha level of 0.05, an anticipated effect size of 0.375, and a desired statistical power of 0.8. A minimum sample size of 113 for each study group was determined.
Physical Training and Daily Physical Activities
The intervention group performed the standard physical training 1.0 ± 0.6 times per week and the additional outdoor circuit training 1.0 ± 0.8 times per week. In total, the intervention group participated in 120.0 minutes of physical training per week. During both standard and additional physical training sessions, most of the time was spent in strength and aerobic fitness training (41.3%), physical fitness tests (19.7%), and team sports (18.4%, Table 2).
The control group performed 1.3 ± 0.5 standard physical training sessions per week for an average duration of 70.7 minutes. Most of the time during standard training was spent on strength and aerobic fitness exercises (38.2%) and on physical fitness tests (33.9%, Table 2).
On comparing the standard training, the intervention group showed a significantly higher frequency in warm-up and cooldown (p = 0.048) and team sports compared with the control group (p = 0.020). All other contents of standard training were similar in frequency and duration between the 2 study groups (Table 2).
The mean PAEE value of the 4 investigated weeks of basic training in the intervention group 9.68 ± 1.57 MJ·d−1 was by trend, but not significantly, higher than in the control group 8.25 ± 1.50 MJ·d−1 (p = 0.237; Table 2). Both study groups covered a similar mean distance of 12.43 ± 2.09 and 11.83 ± 4.41 km·d−1 on foot (p = 0.814), respectively.
Anthropometry and Physical Fitness
There were no significant differences between the 2 study groups in terms of height, weight, or body mass index (Table 1). However, for the control group, a significantly lower level of initial performance in OLS was found compared with the intervention group, whereas the latter showed a significantly lower level of initial performance in PER (p = 0.022 and 0.023, respectively, Table 3). Further, recruits of the intervention group were on average 0.66 years older than those in the control group (p = 0.000, Table 1).
A significant improvement in physical fitness for both study groups was found in OLS, TMS, PER, and SPFT overall score (p < 0.05, Table 3). The intervention group showed greater improvements in OLS, TMS, and SPFT overall score compared with the control group (p < 0.05).
In both study groups, the third of the subjects with the lowest initial physical fitness level improved in all fitness tests and in SPFT overall score (p < 0.05; except for the control group in SLJ, Table 4). For the third of subjects with the highest initial physical fitness level in the intervention group, significant improvements were seen in OLS, TMS, PER, and SPFT overall score (p < 0.05). This specific subgroup showed no improvements only in muscle power. In the control group, the third of subjects with the highest initial physical fitness level did not show any improvements in physical fitness performances (Table 4).
There were no significant differences in the injury incidence rate between the intervention group (14.2 injuries per month per 100 persons) and the control group (13.9 injuries per month per 100 persons; p = 0.423). Furthermore, the overuse injury incidence rate was similar for both study groups (8.7 and 9.1 overuse injuries per month per 100 persons, respectively; p = 0.350).
Chi-square tests showed a significant association between initial physical fitness level in TMS and injury incidence (third of volunteers with lowest initial TMS performances: injury incidence: 65.8%; third of volunteers with highest initial TMS performances: injury incidence: 46.8%, p = 0.011). A similar relationship was seen in the case of overuse injury incidence (lowest TMS level: overuse injury incidence: 50.0%; highest TMS level: overuse injury incidence: 34.2%, p = 0.031). Further, overuse injury incidence was significantly associated with initial physical fitness level in PER (third of volunteers with lowest initial PER performances: overuse injury incidence: 48.0%; third of subjects with highest initial PER performances: overuse injury incidence: 32.1%, p = 0.029).
The 7-week basic military training in the Swiss Army significantly improved physical fitness in both study groups, resulting in increased performances in postural control, trunk muscle fitness, aerobic fitness, and total physical fitness. The intervention group (with standard physical training and additional outdoor circuit training) showed significantly greater improvements in postural control, trunk muscle fitness, and total physical fitness score than the control group (with standard physical training only). There were no differences registered in injury incidence rate between the intervention and the control groups.
Comparisons with other studies in terms of the changes in physical fitness are difficult because of the use of different methodologies. However, the improvements in trunk muscle fitness (11.3 and 29.8%) and aerobic fitness (15.6 and 16.4%) found in this study (Table 3) were comparable with the results presented in studies evaluating similar duration of basic military training (25% in sit-ups, 10 and 13% in 2-mile and 3.2-km run, respectively [9,21]).
The significantly greater improvements in trunk muscle fitness, postural control, and total physical fitness score in the intervention group compared with the control group (Table 3) may be attributed to the higher frequency and varied content of physical training sessions per week. The frequency and total duration of specific strength and aerobic fitness training performed during weekly physical training sessions were higher and longer, respectively, for the intervention group (in 1.6 sessions, a summarized time of 49.6 min·wk−1) than for the control group (in 0.7 sessions, a summarized time of 27.0 min·wk−1, Table 2). Further, the intervention group showed a significantly higher frequency and longer total duration of team sports during standard physical training sessions (in 0.6 sessions, a summarized time of 22.1 min·wk−1) compared with the control group (in 0.1 sessions, a summarized time of 7.1 min·wk−1, Table 2). Most importantly, every additional outdoor circuit training session of the intervention group consisted of specific exercises for trunk muscle strength (prone and side bridge) and balance (single leg balance stand and walking on a balance beam).
Dyrstad et al. (5) conducted a study with a similar 10-week intervention on the frequency and content of physical training sessions among Norwegian infantry soldiers. They found that an average frequency of 1.7 compulsory weekly physical training sessions (30 minutes of running, 31 minutes of strength training, and 12 minutes of other activities) for the intervention group resulted in significant improvements in maximal oxygen consumption (2.5%) and time to exhaustion (7.7%) only. No changes were found for the control group with 0.4 compulsory weekly training sessions (20 minutes of strength training). They found no differences between the control and intervention group for sit-up, push-up, and chin-up performance after the 10-week basic military training (5). These results differ from the findings in this study, demonstrating significant improvements in both study groups not only in aerobic fitness performance but also in postural control, trunk muscle fitness, and SPFT overall score (Table 3).
In accordance with other studies (5,22), for both groups in this study, the third of subjects with the lowest initial physical fitness level showed significant improvements in physical fitness performance during basic military training, whereas the third of subjects with the highest initial physical fitness level showed a significant improvement only in the intervention group (Table 4). Although no individual adaptation of exercise intensity was possible in the standard training, in the additional outdoor circuit training program, exercises were individually adaptable in terms of repetitions and intensity. Therefore, the standard training program alone was probably an insufficient training stimulus for subjects with a high initial physical fitness level. This may explain the fact that recruits with the highest initial physical fitness level improved their physical fitness performances only if they participated in the additional circuit training sessions with individually adaptable exercise intensities.
Ekelund et al. (6) reported PAEE values of 4.6 MJ·d−1 in young civilian men (18.2 ± 1.1 years), whereas in this study, PAEE values of 8.3 and 9.7 MJ·d−1 (Table 2) in Swiss Army recruits were observed. Because intensity and duration of daily physical activities, expressed as PAEE, are relevant for fitness development, it can be concluded that the change from civilian life to the physically more demanding military service has an important influence on physical fitness. Therefore, even without any specific physical training, an increase in recruits' physical fitness level may be very likely. This hypothesis is supported by previous studies (17,22), which reported changes in muscle strength (13.4% in dynamic strength in knee extension and 14.2% in muscular fitness in bench press) and aerobic fitness (4.2% in aerobic capacity) after basic military training (8 and 12 weeks, respectively) including each army's standard physical training.
Injury incidence rates for the intervention and the control group (14.2 and 13.9 injuries per month per 100 persons, respectively) are in the range of values published in meta-analyses of previous review studies (10–15 injuries per month per 100 persons [14,20]). As demonstrated in this study, the higher frequency and duration of physical training, and thus the additional physical demands, in the intervention group were not associated with a higher injury incidence rate. The additional injury risk was probably compensated for by progress in postural control and trunk muscle fitness and by weekly performed active recovery exercises in the intervention group. Such exercises are recommended for injury prevention (3,15,18,23).
It could be demonstrated that a low initial level of aerobic fitness was significantly associated with an increased risk of overuse injury. This result is supported by Shaffer et al. (25) who demonstrated an association between a slower time on the 1-mile timed run and the occurrence of a stress fracture during basic military training. Further, the initial level of TMS performance was significantly associated with overall and overuse injury risk. However, previous studies on the association between trunk muscle fitness measures (as sit-ups test) and risk of injury do not concordantly agree with the present result. Although Knapik et al. (15) showed the same negative association, Jones et al. (11) did not find a relation between sit-up performance and injury incidence. Further studies are needed to investigate the association between initial trunk muscle fitness and injury risk in a military setting.
One of the limitations of this study is that the recommendations of the American College of Sports Medicine (1) were not fulfilled, even with the additional weekly outdoor circuit training session (intervention). The presented results confirm previous observations that the standard physical training is often not implemented as prescribed by the Swiss Army regulations. In fact, only half of the frequency and less than half of the duration prescribed was effectively realized.
A further limitation of the study was the lack of random assignment of volunteers to the intervention and control group. This may explain some of the discrepancies between the 2 study groups such as differences in terms of quantity of team sports in standard physical training, age, and initial level of postural control and aerobic fitness. However, in the Swiss Army, a random assignment of volunteers or companies to intervention and control group is not possible because of organizational limitations. To overcome the lack of random assignment, parameters representing daily physical activities such as PAEE and distances covered on foot were additionally investigated. Because those parameters and the anthropometric and most of the initial physical fitness parameters did not differ between the 2 study groups, the match of intervention and control group in this study is good.
In conclusion, this study has demonstrated that a change from a civilian daily routine to the physically more demanding military routine (including 1 standard physical training session per week) leads to significant improvements in postural control, trunk muscle fitness, aerobic fitness, and total physical fitness score after the 7-week basic military training in the Swiss Army. This effect was particularly demonstrated in recruits with the lowest initial physical fitness level. The implementation of a weekly circuit calisthenics and aerobic fitness training program in addition to the standard physical training resulted in significantly greater improvements in postural control, trunk muscle fitness, and total physical fitness score among the intervention group compared to the control group. The revealed effect was also demonstrated in the subgroup with the highest initial physical fitness level. Therefore, we conclude that a regularly performed additional circuit fitness training program can be helpful to achieve even greater improvements in recruits' physical fitness independent of their initial physical fitness level. Moreover, the additional physical demands resulting from these training sessions did not contribute to an increase the injury rates in the investigated study group.
This study highlights the importance of physical fitness training in military organizations and the need to pay attention to the quantity and quality of implemented physical training sessions, especially in the Swiss Army. Recruits with high initial physical fitness level do not benefit sufficiently from the typical standard physical fitness training. However, an additional outdoor circuit training program was successful in improving the physical fitness (independent of recruits' initial fitness level) and did not increase injury rates within the investigated study group. Hence, it can be concluded that the outdoor circuit training program applied in this study offers a possible solution to the problem of limited infrastructure and personnel shortage in the Swiss Army.
Therefore, we recommend installing outdoor circuit training posters at every casern of the Swiss Army. The implementation of the program is very feasible, and it can help in increasing the number of physical trainings to at least 2 sessions per week, apart from allowing subjects to choose an individualized training intensity. We conclude that outdoor circuit training is an ideal solution for promotion of physical training in a military setting, because it requires minimal time, infrastructure, and personnel support.
The authors thank the military staff and volunteers of the participating study groups from the Swiss Army for their cooperation and participation in this study. They thank the military staff and volunteers of the participating study groups from the Swiss Army for their cooperation and participation in this study. Further, they thank Dr. Rodo O. von Vigier and Dr. Franz Frey from the Swiss Army Medical Services for their help in injury data collection. No funding received for this work.
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