Figures 1 and 2 show the results of the militarily relevant tests. In the 3.2-km run or walk with the 32-kg approach load (Figure 1), the SPT group reduced its mean ± SD time by 14%, from 24.5 ± 3.2 minutes to 21.0 ± 2.8 minutes, whereas the WBT group reduced its time by 15%, from 24.9 ± 2.8 minutes to 21.1 ± 2.2 minutes, with no significant difference in improvement between the 2 groups. In the 400-m run with the 18-kg fighting load (Figure 1), the SPT group reduced its time by 11%, from 94.5 ± 14.2 seconds to 84.4 ± 11.9 seconds, whereas the WBT group reduced its time by 16%, from 100.1 ± 16.1 seconds to 84.0 ± 8.4 seconds, with no significant difference in improvement between the 2 groups. The post-test times of both groups were very similar. In the obstacle course (Figure 2), the SPT group reduced its time by 16%, from 73.3 ± 10.1 seconds to 61.6 ± 7.7 seconds, whereas the WBT group reduced its time by 10%, from 66.8 ± 10.0 seconds to 60.1 ± 8.7 seconds. The improvement in the SPT group was significantly (P < 0.05) greater than in the WBT group. However, the post-test times of both groups were similar. In the 30-m rushes (Figure 2), the SPT group reduced its time by 6%, from 63.5 ± 4.8 seconds to 59.8 ± 4.1 seconds, whereas the WBT group reduced its time by 2%, from 60.4 ± 4.2 seconds to 58.9 ± 2.7 seconds, with no significant difference in improvement between the 2 groups. In the 80-kg casualty rescue (Figure 2), the SPT group reduced its time by 36%, from 65.8 ± 40.0 seconds to 42.1 ± 9.9 seconds, whereas the WBT group reduced its time by 23%, from 57.6 ± 22.0 seconds to 44.2 ± 8.8 seconds, with no significant difference in improvement between the 2 groups. The post-training test scores of the 2 groups were similar.
Figure 3 shows the effects of the 2 types of training on the Army Physical Fitness Test results. In the push-up test, the SPT group increased the number of repetitions by 31%, from 32.2 ± 13.5 to 42.3 ± 10.4, whereas the WBT group increased the number of repetitions by 32%, from 36.3 ± 8.5 to 47.8 ± 10.9, with no significant difference in improvement between the 2 groups. In the sit-up test, the SPT group increased the number of repetitions by 50%, from 36.9 ± 10.9 to 55.4 ± 10.2, whereas the WBT group increased the number of repetitions by 28%, from 39.3 ± 14.6 to 50.3 ± 13.1. The SPT group improvement was significantly greater than the WBT group improvement. In the 3.2-km unloaded run test, the SPT group reduced its run time by 13%, from 16.8 ± 2.5 minutes to 14.6 ± 1.4 minutes, while the WBT group reduced its run time by 12%, from 17.2 ± 3.2 minutes to 15.1 ± 2.2 minutes, with no significant difference in improvement between the 2 groups.
Figure 4 shows the results for jump performance. In the standing vertical jump test, the SPT group increased its vertical jump distance by 1%, from 47.8 ± 8.1 cm to 48.3 ± 7.1 cm, whereas the WBT group increased its vertical jump distance by 5%, from 49.5 ± 7.4 cm to 52.1 ± 7.5 cm, with no significant difference in improvement between the 2 groups. In the standing horizontal jump test, the SPT group increased its horizontal jump distance by 3%, from 214 ± 26 cm to 221 ± 22 cm, and the WBT group also increased its horizontal jump distance by 3%, from 212 ± 31 cm to 219 ± 30 cm, with no significant difference in improvement between the 2 groups.
Figure 5 shows the results of the treadmill maximal oxygen uptake test. The SPT group improved by 10%, from 47.2 ± 5.9 mL·kg−1·min−1 to 51.9 ± 5.4 mL·kg−1·min−1, whereas the WBT group improved by 13%, from 48.1 ± 5.6 mL·kg−1·min−1 to 54.5 ± 5.7 mL·kg−1·min−1, with no significant difference in improvement between the 2 groups.
Figure 6 shows the results of the weight-based training tests. In the bench press, the SPT group improved by 11%, from 77.2 ± 10 kg to 85.5 ± 10 kg, whereas the WBT group improved by 12%, from 72.7 ± 10 kg to 81.2 ± 10 kg. In the barbell squat, the SPT group improved by 10%, from 94.0 ± 14 kg to 103.0 ± 17 kg, whereas the WBT group improved by 12%, from 92.3 ± 6 kg to 103.0 ± 7 kg. In neither weight-based training test was there a significant difference in improvement between the 2 groups.
Although the volunteers in both groups improved significantly in all tests, there were no practical differences in training effect between the 2 programs. The similarity in outcome of the 2 programs may have been related to the comprehensive nature and similarity between both forms of training. Both training programs were designed to cover all major body movements and improve speed, agility, and endurance; started at a moderate level and built up to relatively high intensity; included sprint interval training, requiring the muscles of the lower body to exert high forces at high speeds; and had some sort of agility training that required rapid changes in direction. The main difference between the 2 programs was that one used weight-based training exercises and the other used calisthenics.
The strength improvements by the WBT group in this study, a mean 12% in the bench press and squat, were comparable to those in a study of similar duration and initial volunteer fitness status (23), but less than those in another such study (2). There is little doubt that if the focus of training had been strictly on strength development, changes in strength test scores would have been greater. The lack of dramatic strength gains in the WBT group may be attributed in part to a degree of incompatibility between strength and endurance training. Work by Hickson (12) was the first to elucidate the inhibition of strength gains when strength and endurance training are conducted concurrently. Recent work has attributed the inhibition to interference of intracellular signaling mechanisms. AMPK, activated by endurance exercise, inhibits the activity of mTOR and its targets, thereby blocking signaling to the protein synthesis mechanisms (22). Also, protein kinase B/Akt and AMP-activated protein kinase, respectively, are responsible for strength and endurance adaptations and inhibit each other's downstream signaling (3).
Additional factors could well have contributed to the lack of difference in strength gains between the 2 training groups. The training was restricted to 1.5 hours a day, 5 days a week, to keep within normal Army time strictures. Because workout time had to be allocated to the development of speed, agility, and load carriage ability, weight-based training was limited to twice a week. In addition, the energy devoted to running, interval training, agility drills, and load carriage may have somewhat muted the strength gains. However, there was no evidence of overreaching or overtraining, and the volunteers never stagnated or regressed in their lifts. The intensity of the training was increased gradually, and the volunteers were not deprived of sleep or adequate nutritional intake. The volunteers were civilians who led their normal lives except for their training sessions 1.5 hours a day, 5 days a week.
Many soldiers, particularly those in elite units, engage in weight-based training in the gym facilities that are provided in virtually all military bases. Some unit leaders even direct weight-based training sessions. The authors hypothesized an advantage to WBT over SPT primarily because the resistance provided by barbells, dumbbells, and weight stack machines could reach higher levels than the resistance provided by calisthenics and could be adjusted with more precision to allow exercises to be kept within the range of 1 to 12 repetitions, which produces strength increases (8). Because calisthenics use body weight for resistance, it is more difficult to adjust resistive force than with weights. Thus, for exercises such as push-ups or sit-ups, fit people can do considerably more than 20 repetitions, a range that improves muscular endurance more than muscular strength. However, the predicted advantages of weight-based training did not materialize. The Standardized Physical Training program somewhat compensated for the lesser adjustability of resistance of calisthenics than of weight-based training. For example, most young men can do fewer than 5 pull-ups, and many cannot do any at all. To allow pull-ups to be used for a training exercise, even for those who cannot do any, the Standardized Physical Training program manual specified that a partner could grasp the trainee's legs and provide enough vertical force to enable several repetitions to be performed (7). This technique had to be used with most volunteers, and some progressed so that they could do at least 5 repetitions unassisted.
The improvements in both training groups were not only statistically significant for all of the tests, but also of substantial magnitude in most of the tests. Because the volunteers had not recently engaged in intense, comprehensive exercise programs before the study, they clearly had potential for improvement. Relatively untrained subjects typically respond dramatically to training. Thus, the weightlifting exercises and the calisthenics provided sufficient training stimulus to improve the strength- and power-based physical performance of the volunteers.
Based on their aerobic capability, the volunteers were not an unfit group. Their initial mean o2max of approximately 48 mL·kg−1·min−1 placed them in approximately the 70th percentile for men their age, and their post-training o2max of 52 to 55 mL·kg−1·min−1 placed them in approximately the 85th percentile for men their age (1). It was not unexpected that the volunteers would be of an above-average physical fitness level. Individuals with the desire and confidence to participate in an intense physical training program are likely to be more athletic than average. Second, the medical screening process eliminated individuals above the Army induction weight for height limits and those with high blood pressure or other physical problems. However, the relatively high initial fitness level of the volunteers did not make them less representative of an Army recruit population because similar self-selection and medical-selection factors come into play for those enlisting in the military. Indeed, a study of more than 1,500 U.S. military male recruits showed that they were also relatively high in aerobic fitness compared to civilian men of their age (25).
The 10% to 13% improvement in o2max of the volunteers was considerable, especially because they started out somewhat above average in aerobic fitness and neither group averaged more than 12 km per week of running, including the distance runs and interval training. The degree of improvement one can expect in o2max depends on the pretraining level, and fit volunteers generally show relatively small percentage changes. A reasonable comparison can be made to a group of moderately active college students, who trained by running 10 to 40 minutes at 80% to 90% of their maximal heart rate 3 days a week for 9 weeks and improved 9.3% in o2max (21).
In the timed 3.2-km, 32-kg load carriage trial, some of the volunteers were able to jog the whole distance, whereas others had to walk occasionally. Overall, the volunteers reduced the time taken to cover the distance by approximately 15% in 8 weeks, an improvement that compares favorably with those in other studies. In the studies by Kraemer et al. (18, 20), the 12-week program of weight-based training and high-intensity endurance training produced 11% to 14% improvements in 3.2-km, 44.7-kg load carriage time of men. Among 20 male and 14 female recruits who underwent 10 weeks of British Army recruit training, Williams and Rayson (26) observed a 6.7% improvement in 3.2-km, 15-kg load carriage time, and among 50 male recruits, an improvement of 16% in 3.2-km, 25-kg load carriage time. In the authors' previous 24-week training study, 3 times as long as the current one, women improved by 32.5% in 3.2-km, 34-kg load carriage time (11).
The 8-week training period was used because of the Army's interest in relatively short-term training for recruits and for reservists called up for deployment. However, the relative shortness of the training period may well have contributed to the minimal differences in performance improvement between the 2 training programs. One would expect that weight-based training would allow strength to increase over a longer period than would calisthenics, because weight-based resistance can be increased in precise increments and to an unlimited extent. However, such differences may take somewhat longer to become evident. Indeed, in a 12-week study by Kraemer et al., a weight-trained group continued to show significant improvements in tests of strength and power over a longer period of time than did a group that trained without weights. Thus, it would be valuable to conduct a comparison of training interventions that would extend over several months to determine whether calisthenic training would produce an earlier plateau in simulated battlefield performance than would weight-resisted training.
As with most sports, the primary power for the militarily relevant physical activities tested in this study comes more from the lower body than from the upper body. The muscles in the hips, calves, and thighs propel the body upward and forward with each step in the 3.2-km load carriage test and the 400-m sprint with fighting load. In the obstacle course, these muscles are heavily involved in running, jumping over hurdles, zigzagging, climbing the wall and platform, and running up the stairs. To a lesser extent they are also involved in crawling. The obstacles that bring the muscles of the torso and arms more into play are the crawl and horizontal pipe shimmy. The simulated casualty rescue relies somewhat on grip strength, but the primary movers are also the muscles of the lower body. This helps to explain the similar training effects of the 2 programs. Although the weight-based training program used the barbell squat, barbell step-up, and box jump to strengthen the lower body, the calisthenics program used bodyweight squats, lunges, and jumps. That both programs included exercises that trained the leg and hip muscles to accelerate against gravitational and inertial resistance helps to explain why performance improvements on all the militarily relevant tests, which depend mainly on lower-body power, were similar for the 2 programs.
The U.S. Army for decades has shown a preference for physical training programs and physical fitness tests that do not require the use of equipment. The obvious motivation for this is to control costs and avoid transport, storage, securing, and accounting for equipment. This is why Army physical training has been based in calisthenics and the Army Physical Fitness Test consists of push-ups, sit-ups, and unloaded run, although these tests have not correlated strongly with military performance, such as load carriage speed (9). The Army's Standardized Physical Training program represents a departure from the no-equipment policy, in that it incorporates exercises on a pull-up bar. The purpose for adding such exercises was to improve the soldier's ability to perform climbing maneuvers, such as entering houses through windows and getting over walls, maneuvers that challenge soldiers, especially in the urban environments commonly encountered during current military operations and in possible future conflicts. The Standardized Physical Training manual (7) actually includes construction plans for a 4-bar pull-up station. That the pull-up bars are outdoors and fixed to the ground obviates the need for secure storage and property accountability.
The results of this study support the use of the Army's Standardized Physical Training program for the basic training of recruits. A previous study (17) showed the program's effectiveness in producing fewer recruits who failed the Army Physical Fitness Test than did the Army fitness training that had been the norm until the introduction of the Standardized Physical Training program (1.7% vs. 3.3%) (P = 0.03), while producing 38% fewer injuries. The current results, showing major improvements in simulated battlefield tasks, provide further support for implementation of the standardized program. Currently, the Standardized Physical Training program is mandatory for Initial Entry Training and Advanced Individual Training, which the soldier undergoes before being placed into a regular unit. Afterward, individual Army units have the option of continuing to follow the Standardized Physical Training program or creating their own programs from the exercises listed in Army Field Manual No. 21-20 (5).
Military recruits and called-up military reservists can considerably improve their ability to perform physically demanding combat-related physical activities in 8 weeks of the Army's new Standardized Physical Training program or a weight-based training program. That the standardized Army program does not require moveable equipment that must be stored and accounted for and could be lost or stolen makes it attractive to the Army. The program is well suited to training large groups and could be adapted by schools and other organizations that wish to train large groups for general fitness with minimal equipment. Eight weeks is a relatively short physical training period, and the overload principle makes it likely that individuals trained with weight-based training would continue to improve in strength and, concomitantly, military performance over a longer period than those trained with calisthenics. It is thus important to emphasize that this study in no way negates the potential benefits of weight-based training for longer-term improvement of militarily relevant physical performance. The availability of weight-based training facilities and their use by military personnel would likely enhance the combat readiness of fighting forces.
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Keywords:© 2008 National Strength and Conditioning Association
weight-based training; standardized physical training; exercise testing; Army