Common occupational physical tasks for soldiers can include patrolling long distances in different terrains, carrying and lifting objects with variable weight, and performing explosive movements in the battlefield [1
]. All these requirements create complexity for constructing physical training programs for soldiers. In all, various factors including sex, age, physical training history, nutrition, recovery, and sleep, in addition to psychological, environmental, and social aspects can significantly influence physical training adaptations [2
]. Moreover, optimizing a soldier’s performance in military environments is constantly challenged by external stress factors including carrying loads of various weights, sleep deprivation, extended physical activity, negative fluid and energy balance, and continuous readiness [3
]. These stressors have been shown to cause disruptions in hormonal balance [6
], leading to reduced physical and cognitive performance [3
], prolonged recovery times [14
], and increased susceptibility to infections [15
]. Therefore, training load combined with these external stress factors can lead to compromised training adaptations, overreaching or even overtraining, in addition to increased musculoskeletal injury rates [16
]. All these factors should be carefully considered when planning and implementing optimal physical training programs for soldiers.
To meet the occupational requirements, it is important to determine the best training programs and periodization models for a soldier. Decreased overall physical activity and fitness of recruits creates more demands for their initial training [19
]. The increase in daily activity in garrisons can result in a sudden increase in recruits’ physical activity, which increases the risk of overtraining or injury [16
]. Therefore, it is crucial to have a well-planned and periodized physical training program taking into account the initial physical performance level. In the past, most physical programs have concentrated on improving aerobic endurance of recruits using traditional periodization [2
]. A more suitable approach may be the use of an undulating or a block periodization model with elements of aerobic and anaerobic conditioning and strength training [22
]. In addition, due to strict timetables, physical training should be incorporated into the occupational training of a soldier, and the majority of training should be performed wearing a uniform and in field conditions [28
]. This would help soldiers to train more occupational skills and to better adapt to different terrains: possibly decreasing injuries during training. Both the decline in physical fitness and the higher demands in occupational requirements of the recruits have led to a situation, where systematically designed, tailored, and supervised physical training that meets the occupational task requirements needs to be performed during the basic training [29
]. While designing a training plan for soldiers, it is essential to evaluate the components emphasizing the occupational task requirements. The result of physical training programs relies on training frequency, intensity (velocity and load), and volume (repetitions and duration), which form the foundation of training [2
]. To enhance and optimize training adaptations and to reduce overtraining and training-related injuries in training, it is crucial to plan and organize the training individually. [30
] (p. 205). Nevertheless, it is critical that these emphasized training factors are well related to individual needs, and the initial fitness level of the trainee, and the training plan is well periodized. Additionally, variation in training stimulus is one of the most crucial components when considering the development of explosive or maximal strength and maximal aerobic capacity [30
] (pp. 260–263 and 299–300). Daily military training can be too monotonous and may not enhance a soldier’s physical performance by the best possible way. Professional soldiers should have access to training programs, which first helps them to reach and then to maintain the required level of physical performance [31
In the past, there have been studies regarding specific occupational task tests for soldiers [1
]. These studies have shown that a soldier needs both aerobic and anaerobic endurance and muscle strength to fulfill occupational requirements. Mala et al. [32
] observed that strength and power were strongly related to high-intensity military tasks with and without heavy load carriage. Pihlainen et al. [33
] showed that the maximal countermovement jump (CMJ), 3000 m running time, skeletal muscle mass, and repeated push-ups explained about 60% of military simulation test time. In addition, in a study by Sporis et al. [26
] anaerobic endurance and strength were found to be important factors in the soldiers’ performance. According to the current literature, it seems that there is no “gold standard” to measure soldiers’ occupational physical performance. As a consequence, the most effective way to train to improve these occupational requirements has not been studied sufficiently. Thus, the purpose of this study was to determine which physical abilities are important for soldiers during a repeated simulated military task course and which type of training (task specific, strength, or traditional military fitness training) would be useful and contribute to gains in these abilities during a specialized military training period.
The main finding of the present study showed that STG and TSG improved performance in the simulated military task course more than CON during the first six weeks of the study period (PRE–MID). During the second six weeks of the study (MID–POST), the subjects were able to maintain physical fitness and simulated military task course performance despite the high amount of military field training and the decreased number of physical training sessions.
It is necessary for soldiers to have an appropriate physical performance level, before military field training (MFT) or deployment. As seen previously, MFT may have unfavorable effects on soldier’s physical performance and activity levels [16
]. Hence, it is crucial to have an adequate recovery period after a long military training course or MFT to retrieve combat readiness [39
]. Altogether, military training and deployments create a complicated environment for strength development due to the fact that endurance training is fully integrated into soldiers’ daily training. It has been shown that high (>3 times/week) endurance training frequency, especially with high training volumes, may have a negative influence on strength and, specifically, explosive performance during their concurrent training [40
]. Daily military training may also have a similar effect on the development of different physical characteristics.
When considering the physical performance tests, no significant changes were found between the training groups in all measurements. In the six-second cycling test, maximal power increased in all groups, but STG and TSG improved most between the PRE and MID measurements. In the maximal strength test, only significant improvements were observed in leg press in the TSG group and in bench press in the STG group. In CMJ, small significant improvements were noticed in the TSG and STG groups. Although no differences between groups were observed in the present study, greater improvements took place in the TSG and STG groups in the strength and power tests compared to the CON group. In addition, the improvements were similar in the TSG and STG groups. Thus, it seems that task-specific training is as effective as strength training to improve soldiers’ military task specific performance. This finding is in line with a previous study done in the military environment [43
], where no differences between the training groups were observed.
The total number of training sessions during the 12-week study period was 18. The first six weeks of the study was the actual training intervention period including 12 training sessions. Between the PRE and MID measurements, there was only one MFT, which lasted five days. During other weeks, the subjects had two to three training sessions as described earlier in the methods. The last six weeks of our study can be described as a maintenance period, because the subjects had four different MFTs during this period, lasting from four days to ten days. During this period the subjects had only six training sessions, zero to three times in a week. It has been shown earlier [44
] that more than two sessions per week should be implemented to obtain improvements in strength and power performance in the military environment. In addition, the influence of military training [44
] might have affected the outcome of the present study, especially, during the last six weeks.
Although no significant differences were found between TSG and STG in the simulated military task course, they both improved more than the CON group, especially, between the PRE and MID measurements. In addition, TSG seemed to have larger improvements in most parts of the course compared to STG, which may be explained by specific training with the same tasks as the actual simulated course in TSG [46
]. It is also important to notice that the other groups had similar drills during the regular military training, but with lower volume and intensity. The results in our study support the findings by Harman et al. [43
], where the training groups did high-intensity task-specific training as well. These improvements can also be explained by increased aerobic capacity, which could not be measured reliably in the present study. High-intensity interval training, performed by TSG, has been shown to lead to improvements in both aerobic and anaerobic performance [47
]. Thus, when considering the results, it is possible that the task-specific training had more effect on improving both aerobic and anaerobic performance than strength-focused training. With regard to the improvement in the casualty drag, which involves moving a heavy load as fast as possible, both TSG and STG improved their performance significantly, but no significant changes were found in CON. This was probably due to the training of CON not including any maximal strength or high-power type of exercises. It has been shown in previous studies [29
] that the ability to produce force and power is important in improving performance in these kinds of tasks. If the casualty drag would have been longer, most likely greater differences between TSG and STG compared to CON might have been observed. Furthermore, some indicators may demonstrate the specificity of the training, such as STG improvements in isometric bench press between the PRE and MID measurements while TSG did not, and TSG improved maximal isometric leg press force between PRE and MID while STG did not. This was most likely due to the fact that the main focus in the TSG group was in lower body training, when STG performed also upper body exercises. This finding should be taken into account when planning training programs in the future. Upper body maximal strength has been shown to be important for soldiers’ performance [48
], and especially with field-based training, and must be taken into account when designing training programs. In addition, motivation has been shown to have a major impact to actual performance in these kinds of military task courses. Although all groups had high lactate values, CON seemed to have slightly lower concentrations compared to TSG and STG, but this might be because of their training, which did not include high intensity training.
With regard to the associations between different variables, there was a good correlation between the CMJ and six-second cycling power tests as compared to improved performance in the simulated military task course. This has also been found in previous studies when comparing power production and different task specific courses [32
]. We also observed a significant correlation between time over the first five meters run and maximal upper body strength and push-up tests. Mala et al. [32
] also found a similar association in their study. This can be explained by the type of task, which was performed starting in the prone position followed by standing up to run. This involves upper body extensors, which may be an important factor to perform the actual task [51
]. The present study also showed that increased fat-free mass correlated significantly with the improvement in the simulated military task performance and with the increase in maximal isometric strength. These findings have been [32
] shown to be important factors in evacuation tasks that involve high loads. When considering the PRE times and relative changes between the PRE and MID measurements, there was a significant correlation between the PRE time and magnitude of improvement in TSG and STG. Both task-specific and strength training programs were highly effective for the subjects who performed worse in the PRE measurements. Normal physical training did not have the same effect in CON.
In the present study, an endurance training group was planned to be included in the experimental design but because of a low number of subjects in this group, we had to drop it out of the study. The endurance group and a long duration endurance test would have provided more information on overall physical performance of the simulated military task performance. It should also be pointed out that the small number of the subjects were not fully familiar with all of our measurements prior to the study, because they had missed the familiarization session, but all the subjects were individually instructed in detail before the measurements. In addition, it should be remembered that all tasks in the simulated military test were the same as they performed throughout during their basic military training. In the future studies, it is important to include an endurance test in order to determine what physical abilities matter most in the simulated military task course.
The present study showed that both the task-specific and strength training programs were more effective than that of CON during the first six weeks in improving the performance in the repeated simulated military task course. It is important to have high-intensity training alongside with low-intensity military training to improve soldiers’ task specific performance. The present study showed that task-specific training is as effective as that of strength training to improve the repeated simulated military task course time. This is an important finding, because this kind of training can be carried out without a high amount of equipment and in large groups compared to gym-based strength training. An optimal combination could include high-intensity simulated military task field training and strength focused gym training depending on the military training phase and environmental possibilities. In addition, an intensive six-week training period during the specialized military training can improve physical and military occupational performance in previously trained soldiers. In future studies it is important to compare different training programs over a longer follow-up period. In addition, it seems that it is also possible to maintain these levels of physical and military occupational performance during a six-week intensive military field-training period with only a few physical training sessions.