Implementation of HIIT Sessions to Maintain Physical Preparedness during Military Deployments

Strength and conditioning for soldiers is a complex field due to the wide array of metabolic needs, biomechanical requirements, and the high stakes that are often involved. Ensuring tactical athletes are prepared for their job is of the utmost importance as they could find themselves in high pressure situations at a moment’s notice, therefore maintaining consistently high levels of physical and mental preparedness is paramount. Although there exists a multitude of job requirements and positional needs in the military, deployed military personnel ought to maintain a high level of muscular strength, muscular power, muscular endurance, anaerobic capacity, and aerobic capacity regardless of their specific responsibilities in order to carry out their duties safely and effectively (11). To ensure physical preparedness throughout deployments, a high level of fitness ought to be developed prior to deployment and effectively maintained during deployment. Studies have shown that most deployed soldiers tend to maintain their muscular strength and power throughout the course of a typical six-month deployment; however, their aerobic capacity and performance during endurance-oriented tasks often declines (9). This decline in fitness has been specifically documented across infantry, reserve, and national guard units, with likely declines throughout most military units (1,8). Anecdotally, contextual factors that may contribute to these findings include increased individual freedom for training during deployment combined with many individuals enjoying resistance training more than metabolic conditioning.

Soldier’s diverse needs make incorporating high-intensity interval training (HIIT) sessions in deployed military personnel’s training programs a practical training option due to the aerobic and anaerobic adaptive responses, the time efficient training periods, and relative minimal need for extensive space and extra equipment. HIIT training involves intermittent high-intensity intervals separated by brief rest periods in order to sustain longer periods of high-intensity anaerobic training than would be possible from continuous bouts of training, which can yield a combination of anaerobic and aerobic adaptations. For example, one study demonstrated that performing 10 10-s sprints with a 1:4 work-to-rest ratio not only augmented anaerobic power, but also enhanced VO2max to a similar magnitude as 20 – 25 min of moderate intensity continuous exercise (5). HIIT training when combined with resistance training has been shown to improve VO2max and strength outcomes, making it a valuable programming approach for deployed personnel (2,6).

HIIT Training

The job responsibilities soldiers must be prepared for require varying degrees of muscular strength, muscular endurance, and metabolic capacity. Tasks such as marching, digging, rucking, patrolling, preparing forward operating camps, running, jumping, carrying heavy loads, and casualty evacuation are all examples of duties a soldier could undertake in the line of duty (7,8,12). Metabolically, these responsibilities require heavy involvement of both aerobic and anaerobic mechanisms as well as prerequisite muscular strength and muscular power (12). As a result, training for active duty tasks typically involves some combination of resistance training and metabolic conditioning. A reasonable concern when training for multiple goals at the same time is the concurrent training effect (CTE), where the combination of resistance training and endurance training yields some degree of suboptimal adaptations. Although there are conflicting findings in the literature regarding the extent of the CTE’s impact, it has generally been shown to have a notable blunting effect on muscular power and relatively minor effects on muscular strength and hypertrophy (6). Yet, the use of HIIT has been shown to minimize the negative consequences related to the CTE, which has significant implications for tactical athletes who train for multiple training goals simultaneously (4). Consequently, soldiers would benefit from HIIT implementation in the development and maintenance of physical preparedness throughout their career, although maximum value may be realized during deployments. HIIT offers similar adaptations to traditional high-volume, low-intensity endurance training, while being more time efficient, minimizing training volume, maintaining training intensity, and curtailing negative effects on resistance training-induced adaptations (4,6).

Further, one study demonstrated that performing HIIT in conjunction with heavy resistance training can simultaneously improve VO2max and muscular strength (6). In this study, a statistically significant difference was found in VO2max outcomes for the experimental group who only performed 12 min of Tabata-style HIIT cycling sessions compared to the control group who performed 60 min continuous cycling sessions (6). The HIIT group also demonstrated considerable progression in lower extremity strength throughout the duration of the six-week intervention. A direct comparison of HIIT with continuous aerobic training demonstrates the efficiency and effectiveness of programming HIIT sessions in conjunction with strength-focused resistance training for tactical athletes. Another study found concurrently resistance training and performing Tabata-style HIIT to increase maximal anaerobic power to a greater extent than HIIT alone (10). For military personnel, training anaerobic power can allow for improved performance during repeated effort tasks, such as those encountered in combat scenarios (11).

“A direct comparison of HIIT with continuous aerobic training demonstrates the efficiency and effectiveness of programming HIIT sessions in conjunction with strength-focused resistance training for tactical athletes.”

In soldiers, the implementation of a training regimen combining resistance training with HIIT has the potential to yield the aerobic, anaerobic, and resistance-training related adaptations crucial for maintaining optimal physical readiness during deployment. Deployed soldiers can be expected to have the prerequisite level of aerobic conditioning necessary for appropriately programmed HIIT, making this training option a safe and readily implementable alternative. Continuous aerobic training still has a place in soldier training, yet deployed soldiers often lack the space, equipment, or time necessary to effectively maintain or improve aerobic fitness. For soldiers preparing for deployment, general recommendations include alternating continuous aerobic training and HIIT training to ensure familiarity with both styles prior to deployment.

Military Deployments

During overseas deployments, military personnel often have limited time to access training facilities due to their job requirements, which means they must be more creative in how they maintain their level of fitness throughout the duration of their deployment (9). Most soldiers during deployment will have access to some form of training equipment, be it aerobic equipment or strength training equipment (8). Yet, deployed soldiers have historically demonstrated a decline in physical preparedness, and thus, mission readiness (8). Studies have shown military personnel can maintain or improve their muscular strength and lean mass, yet they often demonstrate a decrease in running endurance performance and VO2max (9). One study found a significant decrease in aerobic training frequency and duration during deployment to be major contributing factors, which supports another article that points to detraining effects as an underlying cause (7,8). Prior to deployment, 80% of soldiers in the study reported aerobic exercise at least three times per week, while only 35% of these soldiers maintained this frequency during their deployment (8). Additionally, 78% reported their aerobic training sessions to last over 30 min prior to deployment, while 57% reported maintaining this duration during deployment (8). While the physically demanding job requirements of soldiers along with the environmental stressor of deployment are not always conducive for physical training, it is still important for soldiers to maintain physical readiness levels so they can remain prepared for combat.

Apart from the role of aerobic fitness in mission preparedness, it has also been shown to be a predictor for injury, with diminished aerobic capacity associated with greater medical resource utilization in military populations (1,9). Thus, it is in the best interests of tactical athletes to maintain their pre-deployment levels of fitness throughout their deployment, which involves resistance training to maintain muscular strength and power along with training aerobic capacity to maintain endurance performance (2). HIIT’s aerobic and neuromuscular adaptations with less total training time in comparison to traditional low- to moderate intensity aerobic training makes HIIT a practical training method when soldiers’ allocated time to train and access to training facilities is limited (3).

Implementation and Practical Application

The use of HIIT training for aerobic capacity maintenance in conjunction with resistance training for muscular strength and power could yield great benefit for deployed military populations. Given the demonstrated reduction in training frequency and duration for soldiers during deployments, it would be beneficial to program HIIT combined with resistance training in order to maximize the stimulus of each training session and minimize potential detraining effects (8). Additionally, one study demonstrated that HIIT closely simulates military combat in terms of the stress experienced, suggesting HIIT as a superior stimulus regarding its ability to psychophysiologically mimic combat situations in a way that may improve a soldier’s operability and mission effectiveness (11). The HIIT protocol in this study consisted of a three sets of 10 repetitions of 30 s of high-intensity running at >95% maximum heart rate (HRmax), with 30 s rest between repetitions and five min of low-intensity running at <65% HRmax between sets (11). Another study implemented strength training sessions followed by a Tabata-style HIIT protocol consisting of 1 – 3 sets of eight repetitions of 20 s intervals at 150% VO2max with 10 s of rest between repetitions (6). Research has shown three aerobic sessions per week to be successful in maintaining or improving the aerobic fitness of soldiers during their deployment (7). When considering the available evidence, a recommended training protocol consists of three days per week of aerobic training paired with three days per week of resistance training. The use of HIIT induces an amount of fatigue that may negatively affect subsequent training bouts and thus it may be beneficial to perform such training at a frequency of twice per week. Accordingly, a sample program (Table 1) may consist of three total body resistance training days, two HIIT training sessions, and one continuous aerobic training session. Deployed military personnel should consider adding HIIT sessions to their training programs in a manner similar to the provided protocol in order to mitigate the risk of losing the pre-deployment levels of aerobic fitness while concurrently maintaining or improving muscular strength.

Table 1. Sample Program

* Moderate intensity readily indicated via talk test: ability to sing indicates low intensity, ability to comfortably talk indicates moderate intensity, and inability to talk without gasping for breath indicates vigorous intensity

** HRmax often estimated using Gelish method: 207 – (0.7 x age in years) = HRmax in beats per minute (BPM)

*** Potential substitutions for units constrained by equipment or space limitations include rowing, biking, stair climbing, SkiErg, jump rope, burpees, or mountain climbers in keeping with the designated interval durations and intensities

HIIT is a time-efficient method of training both aerobic and anaerobic endurance and can easily be paired with resistance training to optimize muscular strength and metabolic capacity, both of which are essential to the duties of the deployed soldier. To allow for recovery, three non-consecutive HIIT training days are recommended due to the stress of the high-intensity stimulus. However, depending on the needs of the soldier and the context of the program, one of the metabolic training days could be maintained as a traditional low- to moderate-intensity steady-state aerobic training session if ample time is available. However, given the similarity of aerobic stimuli, the primary advantage of continuous training over HIIT would not be aerobic adaptations, but rather mental preparation for longer duration job-related tasks, such as long rucks or marches (3). To maximize training adaptations, literature supports the intra-session exercise sequence of resistance training before endurance training (6). While HIIT is challenging, there are many implications supporting the inclusion of this training modality for the deployed soldier, including improved job readiness and injury risk reduction. To be effective in initiating meaningful change, these tactical athletes must be informed of the current trend of lost aerobic fitness during deployments, educated on the benefits of HIIT regarding its anaerobic and aerobic adaptative potential, and provided with basic guidelines for utilizing HIIT in an evidence-based manner. Overall, HIIT is an efficacious and efficient method of addressing the metabolic training needs of soldiers while they serve their country during deployment.

This article originally appeared in TSAC Report, the NSCA’s quarterly, online-only publication geared toward the training of tactical athletes, operators, and facilitators. It provides research-based articles, performance drills, and conditioning techniques for operational, tactical athletes. The TSAC Report is only available for NSCA Members. Read more articles from TSAC Report

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