TSAC Research Review, Issue 46

by Rod Pope, PhD
TSAC Report June 2017

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This article is the eleventh in a continuing series of tactical strength and conditioning (TSAC) research reviews. It is designed to bring awareness to new research findings of relevance to tactical strength and conditioning communities.

Military Police, both Transit Police and Special Operations Police, Lose Physical Fitness over Time in Service

Jarbas Rállison Domingos-Gomes and colleagues recently published results of a study in which they examined and compared the health-related physical fitness (HRPF) of 22 transit police personnel and 25 special operations police personnel from the Brazil Military Police (3). The study also assessed the impact of time in service on HRPF of both groups (3).

The transit police and special operations police differed significantly only in relation to flexibility, measured with a sit-and reach test, which was 22% greater in the special operations police (3). They were similar in terms of dynamic strength, localized muscle endurance, maximum 20-m shuttle run speed and relative VO2max, with the latter averaging a very reasonable 43 – 46 ml/ kg/min (3). Both groups were typically overweight, based on average body mass index (BMI) measurement of 27 – 28 kg/m2 (3). They also had an average waist circumference of 93 cm and an average body fat percentage of 20 – 21% (3).

Notably, in both groups, there were moderate correlations between length of service and measures of HRPF, including waist circumference, body fat percentage, dynamic strength, localized muscle endurance, and relative VO2max (3). As length of service increased, each of these indicators of HRPF deteriorated (3). Additionally, all of these changes in HRPF were more pronounced in the transit police group (3).

The authors concluded that the more significant deterioration in HRPF measures over time observed in transit police may be due to differences in activity levels related to the respective occupational roles (3). In particular, they suggested that transit police may spend more time in sedentary activities compared to the special operations police. They additionally noted reductions in HRPF levels give rise to a heightened injury risk, which may reduce efficiency and professional performance in the job, both of which are concerns of particular importance to police officers who have been in the job longer (3). Their recommendation was the implementation of a physical training program designed to improve HRPF and hence occupational performance in these military police (3). For the tactical facilitator, this study serves as a reminder of the importance of why personnel need to maintain their fitness levels through regular and appropriately designed exercise, across their career-span.

Army 1-1-1 Fitness Assessment Results have Utility for Estimating Risks of Acute and Overuse Injuries in Trainees

JoEllen Sefton and colleagues, discussed the challenges for personnel readiness that musculoskeletal injuries (MSI) create for military forces in a recent research publication (5). They also noted that, while a range of screening methods are being developed to help identify military trainees at greater risk of MSI so that they can receive tailored preparatory exercise interventions, many of these screening tests require specialized personnel, systems, or equipment to be implemented (5). Sefton and colleagues therefore sought to examine whether the United States Army 1-1-1 fitness assessment could be used as a MSI screening tool, noting that this test is comprised of maximum push-ups in one minute, maximum sit-ups in one minute, and time required to run one mile (5). It can also be implemented without any specialized equipment, systems, or personnel (5).

The results of the study by Sefton and colleagues, which involved 1,788 male Army trainees undertaking one of several training programs, indicated that overuse injury risk increased in Army trainees as their one-mile run time increased (5). Furthermore, acute injury risk increased with one-mile run time and with decreasing scores on a FitSum, which is the sum of maximum push-ups in 1 min and maximum sit-ups in 1 min (5). While they acknowledge that these findings were mostly not unexpected, Sefton and colleagues took the application of these results a step further, creating a Microsoft Excel® spreadsheet (which can be found as supplementary material at: http://dx.doi. org/10.4085/1062-6050-51.9.09.S1) to automate the calculation of risk scores (or probabilities) for both acute and overuse MSIs in Army trainees from a number of different training programs (5).

A note of caution is warranted here, as the authors note that the probabilities of any individual trainee with specific Army 1-1-1 test scores suffering an overuse or acute MSI are influenced by the training program they are undertaking (5). Additionally, different training programs have different overall rates of injury (5). In this instance, the authors determined the MSI risks for each of several different training programs, but it should be noted that other programs may have different rates of injury to those observed by Sefton and colleagues and this might impact on the accuracy of any risk estimates based on the spreadsheet (5).

Nevertheless, this article and the supplementary spreadsheet constitute a good practical example of how statistical modelling can be utilized to develop simple screening tools to use in the field to assess risks of MSI (5). In addition, where training programs and populations are similar to those described by Sefton and colleagues, the MSI risks predicted by their spreadsheet based on Army 1-1-1 test results may be reasonably good estimates of actual MSI risks (5). Perhaps of greatest importance for the tactical facilitator, this article provides further evidence that adequate aerobic fitness and muscular endurance are essential in the quest to reduce injury risks in tactical athletes, and this should provide further impetus for well-designed strength and conditioning programs that are tailored to the individual and their assessed conditioning deficiencies (5).

Heat Exposure and Dehydration: Which has the Greatest Impacts on Core Temperature, Mood, and Visual Vigilance?

In a recent study, Elizabeth Adams and colleagues sought to disentangle the effects of heat exposure and dehydration on core temperature, mood, and visual vigilance (1). They began by noting that because heat exposure and dehydration often coincide, it can be difficult to ascertain which variable has the greatest impact on core temperature, mood, and vigilance during tasks like load carriage (1).

To address this issue, they conducted a study involving 12 male participants who each completed four 90-min load carriage trials on a treadmill with a rucksack weighing 45 lb and speed of walking set to achieve a workload of approximately 50% of VO2max with a 5% gradient (1). The first of these trials (T1) was conducted in a euhydrated state (normal level of body water content) and in temperate ambient conditions (approximately 18 degrees centigrade and 50% relative humidity), so there was no dehydration and no heat exposure (1). A second trial (T2) was conducted in which the participants were in a hypohydrated (reduced hydration) state, but again not exposed to heat (1). In the third trial (T3), they were not hypohydrated (normal level of body water content) but they were exposed to hot ambient conditions (approximately 34 degrees centigrade and 45% relative humidity) (1). In the fourth trial (T4), they were exposed to both the hypohydration and the hot ambient conditions (1).

Both the dehydration in T2 and the heat exposure in T3 resulted, on average, in a slightly higher core body temperature (0.39 and 0.36 degrees Celsius rises, respectively) than occurred in the least stressful scenario, T1 (1). Therefore, individually, dehydration and heat exposure had similar, small effects on core temperature (4). However, when both dehydration and heat exposure occurred together in T4, the core temperature increase was greater, reaching around 1.1 degrees Celsius higher than the core temperature in T1 (1). Heart rates also reached their highest levels in T4, in fact 15 – 20 beats per minute (bpm) higher than in the other trials (1).

The combination of heat exposure and dehydration in T4 also elicited much greater negative mood effects than the other trials, including feelings of fatigue and higher scores in respect to measures of confusion-bewilderment and depression-dejection, particularly (1). The average negative mood effect score in T4 was twice as great as in T3, where the participants were exposed to heat alone, and 10 times as high as in T2 and T1 (1). However, despite these mood and core temperature changes, visual vigilance was unaffected in T2 and T4 when compared to T1 (1).

On this basis, it is fair to say that when carrying loads, tactical athletes are exposed to heat and dehydration at the same time. When this occurs, they will be far more affected by core body temperature rises, feelings of fatigue, negative and demotivating moods, and increases in heart rate than when they are exposed to heat or dehydration alone, or neither. Nevertheless, in the case of mood effects, heat exposure alone was observed in this study to have a greater impact than dehydration alone (1). Adams and colleagues note that changes in core body temperature can give rise to heat illness, and that changes in mood can affect occupational performance (1). Increases in heart rate also signify greater workloads for the cardiorespiratory system, meaning the activity being performed will be less easily sustained.

All of this information is valuable to the tactical facilitator, who can encourage tactical athletes undertaking load carriage and other tactical tasks to ensure they maintain adequate hydration when exercising in hotter conditions. Using this information, they can also monitor personnel in hot conditions in order to identify any readily detectable early warning signs of heat stress, like heart rate increases and negative mood effects. Furthermore, tactical athletes can potentially be taught to recognize some of these early warning signs themselves and self-regulate both their levels of hydration and their exercise intensity and continuance in order to manage the associated risks. Importantly, Adams and colleagues also found that tactical athletes who were dehydrated when carrying loads in hot conditions had a much stronger sense of thirst than those who were well hydrated in hot conditions (1). This is reassuring, as it means that thirst, as well as increases in fatigue, heart rate, and negative mood effects, can warn tactical athletes that they need to drink.

Special Warfare Combatant-Craft Crewman Exhibit Similar Postural Stability Whether Wearing Tactical Gear or Not

Paul Morgan and colleagues recently published the results of a study of eight United States Naval Special Warfare Combatant-Craft Crewmen, comparing the postural stability (or balance) of crewmen wearing tactical gear weighing around 22 kg to crewmen not wearing any tactical gear. The authors note that these crewmen “perform special missions on small, high-speed water craft on ocean and small river water systems for insertions and extraction of Special Operations Forces,” (4). On this basis, the authors note that balance ability is important to these crewmen (4).

Interestingly, what they found in their small-scale randomized crossover trial was that the postural stability of these crewmen did not change, regardless of whether they were wearing tactical gear or not (4). The research team hypothesised that this might be because the crewmen were well adapted to wearing the tactical gear and keeping their balance (or good postural control) while on the constantly-moving platform of the water craft they operate. The authors also acknowledged that the small number of participants in their study may have obscured any differences that might have been detected in a larger sample of participants (4). However, these interesting results certainly warrant further research in larger samples of crewmen, as the authors suggest (4).

For the tactical facilitator, these results and results of future studies in this area are interesting, as they may mean that if tactical athletes regularly train for balance when wearing tactical gear, they may develop better balance for when they are required to operate in that gear. The specificity in such a training approach may help to reduce the balance impairments associated with wearing tactical gear that Morgan and colleagues identified have been observed in soldiers carrying loads, for example (4).

Aerobic Fitness and Ventilatory Thresholds Affect Professional Firefighters’ Ease of Task Performance and Air Depletion Rates

Stephanie Windisch and colleagues recently published a study that examined whether greater levels of physical fitness helped to reduce the time firefighters require to complete a series of tasks, the cardiorespiratory strain they experience from completing the tasks, and the amount of air they deplete from their self-contained breathing apparatus (SCBA) (6). The study involved 41 professional firefighters who participated in fitness testing and a simulated series of firefighter tasks (20-m ladder climb, 200-m treadmill walk, pulling a wire rope hoist 15 times, and crawling 50 m in an orientation section) (6). Their performance was evaluated by recording the time to complete the series of tasks, their mean heart rate throughout, and the volume of air depleted from their SCBA (6). These performance measures were combined to form a “time-strain-air depletion” (TSA) score, which summarized their overall performance on the tasks (6).

Three factors predicted individual firefighter performance during the tasks, as assessed by the TSA score (6). The first factor was the VO2peak the firefighters were able to achieve on a maximal incremental treadmill test (6). The second factor was the total time they were able to operate below their ventilator threshold, which was assessed via heart rate monitoring (6). The third factor was their average breathing rate during the series of tasks (6).

Bringing all of these factors together; the authors noted that firefighters who exhibited greater aerobic fitness were able to operate longer at a comfortable and sustainable workload (6). Additionally, they were able to keep their heart and breathing rates at a lower level while performing at an enhanced level (6).

Specifically, they completed the series of simulated firefighting tasks quicker, with less cardiorespiratory strain and with lower rates of air depletion (6).

In practical terms, this means that, after finishing the series of assigned tasks, firefighters with these specific enhanced fitness attributes retained more air in their SCBA than others (who performed less well) and were exposed for less time to the range of hazards and risks that might have been present in the task setting. Conceivably, this would mean that these better conditioned firefighters would also have been more capable to continue with further tasks than their less fit counterparts and would have been exposed to less risk from cardiorespiratory strain and contextual exposure.

Of note for the tactical facilitator, the authors commented that the firefighters in their study reached their ventilatory threshold at around 50% of their VO2peak and that this is a relatively low level (6). With this in mind, they suggested that firefighters like those in their study may benefit from more endurance training to potentially increase their ventilatory threshold relative to their VO2peak (6). Doing this would enable the firefighters to perform higher workloads aerobically with greater sustainably, thus reducing their cardiorespiratory strain and SCBA air depletion rates in any given firefighting task. The authors also noted that the firefighters’ ability to work sustainably and without excessive cardiorespiratory strain can be readily assessed in the field by monitoring heart rates, time to completion, and amount of air depletion during a standardized, simulated firefighting exercise, such as the series of tasks described in their study (6). They further noted that a TSA score can be calculated by summing the average heart rate, time to complete, the task and amount of air depleted during a standardized simulation exercise (6). This TSA score can then be used as a basis for assessing changes in firefighters in occupational performance capacity; for example, after a conditioning program incorporating endurance training.

Aerobic Fitness does not Influence Firefighter Error Rates in a Balance Test but does Affect Self-Selected Speed of Test Completion, both Before and After a Live Fire Suppression Task

Similar to the study by Windisch and colleagues, a recent study by Deanna Colburn and colleagues also investigated the impacts of aerobic fitness on firefighter performance (2). However, this study’s main focus of performance was the rate of stepping errors and speed of completion during a balance test conducted before and after a live fire suppression activity (2).

Twenty-four firefighters of varying aerobic fitness levels participated in this study, and underwent a balance test involving walking forwards and backwards across a beam while in full protective gear, including SCBA (2). They undertook this test before and after a 20-min live fire suppression activity and were instructed to complete the balance test as quickly as possible without making stepping errors (2). The time taken to complete the task was measured with a stopwatch and errors were monitored and recorded (2).

Rates of stepping errors, such as stepping off the balance beam accidentally, were similar, regardless of level of fitness (2). However, firefighters who were less fit selected a speed at which they undertook the balance test that was slower than that adopted by fitter firefighters (6). This finding is clearly consistent with the findings of Windisch and colleagues, who also observed that firefighters who were less aerobically-fit took longer to complete a series of simulated firefighting tasks (6). However, Colburn and colleagues suggest that this strategy of less fit firefighters slowing down their speed of movement may be protective, to prevent them from losing balance and stepping where they should not. The authors do, however, acknowledge that further research is needed to further test that hypothesis (2).

For the tactical facilitator, the information from this study by Colburn and colleagues adds another perspective to that provided by Windisch and colleagues, by suggesting that less fit firefighters do not just work more slowly to make their workload sustainable for their level of aerobic fitness, but may also work more slowly to prevent stepping and balance errors related to their lower levels of fitness and capacity to move precisely at speed (2,6). On this basis, efforts to build the aerobic fitness of firefighters in occupationally-relevant ways while simultaneously developing their balance, agility, and speed of movement in safe ways may pay dividends for their performance and safety on the job.

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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References 

1. Adams, E, Casa, D, Huggins, R, DeMartini, J, Stearns, R, Kennedy, R, et al. Heat exposure and hypohydration exacerbate physiological strain during load carrying. Published ahead of print. The Journal of Strength and Conditioning Research, February 8, 2017.

2. Colburn, D, Suyama, J, Reis, S, and Hostler, D. Cardiorespiratory fitness is associated with gait changes among firefighters after a live burn training evolution. Safety and Health at Work. 2016. Retrieved 2017 from http://dx.doi.org/10.1016/j. shaw.2016.11.001.

3. Domingos-Gomes, J, Oliota-Ribeiro, L, de Sousa Silva, J, de Melo, A, Neto, S, Cirilo-Sousa, M, and Aniceto, R. Comparison of health-related physical fitness and its association with the length of service between special operations and traffic military police officers. Journal of Physical Education 27: e2743-2755, 2016.

4. Morgan, P, Williams, V, and Sell, T. Postural stability of special warfare combatant-craft crewmen with tactical gear. Journal of Special Operations Medicine 15(4): 7-11, 2016.

5. Sefton, J, Lohse, K, and McAdam, J. Prediction of injuries and injury types in army basic training, infantry, armor, and cavalry trainees using a common fitness screen. Journal of Athletic Training 51(11): 849-857, 2016.

6. Windisch, S, Seiberl, W, Schwirtz, A, and Hahn, D. Relationships between strength and endurance parameters and air depletion rates in professional firefighters. Scientific Reports 7: 44590-44600, 2017

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Rod Pope is currently a Professor of Physiotherapy at Charles Sturt University and co-leads the Tactical Research Unit headquartered at Bond Universit...

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