Andrew P. Hunt

The intraocular pressure response to dehydration: a pilot study

The aim of this study was to determine the intraocular pressure response to differing levels of dehydration. Seven males participated in 90xa0min of treadmill walking (5xa0kmxa0h−1 and 1% grade) in both temperate (22°C) and hot (43°C) conditions. At baseline and 30xa0min intervals intraocular pressure, nude body mass, body temperature and heart rate were recorded. Statistically significant interactions (pxa0<xa00.05) were observed for intraocular pressure (hot condition: baseline 17.0xa0±xa02.9, 30xa0min 15.6xa0±xa03.5, 60xa0min 14.5xa0±xa03.7 and 90xa0min 13.6xa0±xa02.9xa0mmHg; temperate condition: baseline 16.8xa0±xa02.7, 30xa0min 16.5xa0±xa02.6, 60xa0min 15.8xa0±xa02.5 and 90xa0min 15.7xa0±xa01.8xa0mmHg) and body mass loss (hot condition: 30xa0min −1.07xa0±xa00.35, 60xa0min −2.17xa0±xa00.55 and 90xa0min −3.13xa0±xa00.74%; temperate condition: 30xa0min −0.15xa0±xa00.11, 60xa0min −0.47xa0±xa00.18 and 90xa0min −0.78xa0±xa00.25%). Significant linear regressions (pxa0<xa00.05) were observed for intraocular pressure and body mass loss (adjusted r2xa0=xa00.24) and intraocular pressure change and body mass loss (adjusted r2xa0=xa00.51). In conclusion, intraocular pressure was progressively reduced during a period of exercise causing dehydration, but remained relatively stable when hydration was maintained. The present study revealed a moderate relationship between dehydration (body mass loss) and intraocular pressure change.

Heat strain during explosive ordnance disposal.

Bomb technicians perform their work while encapsulated in explosive ordnance disposal suits. Designed primarily for safety, these suits have an unintended consequence of impairing the bodys natural mechanisms for heat dissipation. Consequently, bomb technicians are known to experience symptoms of heat illness while performing their work. This research provides the first field based analysis of heat strain in bomb technicians. Six participants undertook simulated operational tasks across 2 days of variable climate. All subjects demonstrated high levels of heat strain as evidenced by elevated heart rate, core body temperature, and physiological strain index. Participants also reported signs and symptoms associated with heat illness. These results were exacerbated by more intense physical activity despite being undertaken in a cooler environment. The universal experience of heat strain in this sample has significant implications for the health of bomb technicians and additional research examining methods to improve temperature regulation and performance is warranted.

Heat strain and hydration status of surface mine blast crew workers.

Objective: Dehydration and symptoms of heat illness are common among the surface mining workforce. This investigation aimed to determine whether heat strain and hydration status exceeded recommended limits. Methods: Fifteen blast crew personnel operating in the tropics were monitored across a 12-hour shift. Heart rate, core body temperature, and urine-specific gravity were continuously recorded. Participants self-reported fluid consumption and completed a heat illness symptom inventory. Results: Core body temperature averaged 37.46 ± 0.13°C, with the group maximum 37.98 ± 0.19°C. Mean urine-specific gravity was 1.024 ± 0.007, with 78.6% of samples 1.020 or more. Seventy-three percent of workers reported at least one symptom of heat illness during the shift. Conclusions: Core body temperature remained within the recommended limits; however, more than 80% of workers were dehydrated before commencing the shift, and tended to remain so for the duration.

Symptoms of heat illness in surface mine workers

ObjectiveTo assess the symptoms of heat illness experienced by surface mine workers.MethodsNinety-one surface mine workers across three mine sites in northern Australia completed a heat stress questionnaire evaluating their symptoms for heat illness. A cohort of 56 underground mine workers also participated for comparative purposes. Participants were allocated into asymptomatic, minor or moderate heat illness categories depending on the number of symptoms they reported. Participants also reported the frequency of symptom experience, as well as their hydration status (average urine colour).ResultsHeat illness symptoms were experienced by 87 and 79xa0% of surface and underground mine workers, respectively (pxa0=xa00.189), with 81–82xa0% of the symptoms reported being experienced by miners on more than one occasion. The majority (56xa0%) of surface workers were classified as experiencing minor heat illness symptoms, with a further 31xa0% classed as moderate; 13xa0% were asymptomatic. A similar distribution of heat illness classification was observed among underground miners (pxa0=xa00.420). Only 29xa0% of surface miners were considered well hydrated, with 61xa0% minimally dehydrated and 10xa0% significantly dehydrated, proportions that were similar among underground miners (pxa0=xa00.186). Heat illness category was significantly related to hydration status (pxa0=xa00.039) among surface mine workers, but only a trend was observed when data from surface and underground miners was pooled (pxa0=xa00.073). Compared to asymptomatic surface mine workers, the relative risk of experiencing minor and moderate symptoms of heat illness was 1.5 and 1.6, respectively, when minimally dehydrated.ConclusionsThese findings show that surface mine workers routinely experience symptoms of heat illness and highlight that control measures are required to prevent symptoms progressing to medical cases of heat exhaustion or heat stroke.

Heat strain during military training activities: The dilemma of balancing force protection and operational capability

ABSTRACT Military activities in hot environments pose 2 competing demands: the requirement to perform realistic training to develop operational capability with the necessity to protect armed forces personnel against heat-related illness. To ascertain whether work duration limits for protection against heat-related illness restrict military activities, this study examined the heat strain and risks of heat-related illness when conducting a military activity above the prescribed work duration limits. Thirty-seven soldiers conducted a march (10 km; ∼5.5 km h−1) carrying 41.8 ± 3.6 kg of equipment in 23.1 ± 1.8°C wet-bulb globe temperature. Body core temperature was recorded throughout and upon completion, or withdrawal, participants rated their severity of heat-related symptoms. Twenty-three soldiers completed the march in 107 ± 6.4 min (Completers); 9 were symptomatic for heat exhaustion, withdrawing after 71.6 ± 10.1 min (Symptomatic); and five were removed for body core temperature above 39.0°C (Hyperthermic) after 58.4 ± 4.5 min. Body core temperature was significantly higher in the Hyperthermic (39.03 ± 0.26°C), than Symptomatic (38.34 ± 0.44°C; P = 0.007) and Completers (37.94 ± 0.37°C; P<0.001) after 50 min. Heat-related symptom severity was significantly higher among Symptomatic (28.4 ± 11.8) compared to Completers (15.0 ± 9.8, P = 0.006) and Hyperthermic (13.0 ± 9.6, P = 0.029). The force protection provided by work duration limits may be preventing the majority of personnel from conducting activities in hot environments, thereby constraining a commanders mandate to develop an optimised military force. The dissociation between heat-related symptoms and body core temperature elevation suggests that the physiological mechanisms underpinning exhaustion during exertional heat stress should be re-examined to determine the most appropriate physiological criteria for prescribing work duration limits.

Developing Physical Capability Standards That are Predictive of Success on Special Forces Selection Courses

This study aimed to develop minimum standards for physical capability assessments (vertical jump, sit and reach, push-ups, seven-stage sit-ups, heaves, agility, 20-m shuttle run, loaded 5-km pack march, and 400-m swim) that candidates must pass before they can commence Australian Army Special Forces (SF) selection courses. Soldiers (Part A: n = 104; Part B: n = 92) completed the physical capability assessments before commencing a SF selection course. At the beginning of these selection courses, participants attempted two barrier assessments (3.2-km battle run and 20-km march). Statistical analysis revealed several physical capability assessments were associated with performance on the barrier assessments and selection course outcome (Part A); however, these statistical models were unable to correctly classify all candidates as likely to pass or fail the selection course. Alternatively, manual analysis identified a combination of physical capability standards that correctly classified 14% to 18% of candidates likely to fail, without excluding any candidates able to pass (Part A). The standards were applied and refined through Part B and included completing the 5-km pack march in ≤45:45 minutes : seconds, achieving ≥level five on the sit-up test, or completing ≥66 push-ups. Implementation of these standards may reduce attrition rates and enhance the efficiency of the SF recruitment process.

Negligible heat strain in armored vehicle officers wearing personal body armor.

ObjectivesThis study evaluated the heat strain experienced by armored vehicle officers (AVOs) wearing personal body armor (PBA) in a sub-tropical climate.MethodsTwelve male AVOs, aged 35-58 years, undertook an eight hour shift while wearing PBA. Heart rate and core temperature were monitored continuously. Urine specific gravity (USG) was measured before and after, and with any urination during the shift.ResultsHeart rate indicated an intermittent and low-intensity nature of the work. USG revealed six AVOs were dehydrated from pre through post shift, and two others became dehydrated. Core temperature averaged 37.4 ± 0.3°C, with maximums of 37.7 ± 0.2°C.ConclusionsDespite increased age, body mass, and poor hydration practices, and Wet-Bulb Globe Temperatures in excess of 30°C; the intermittent nature and low intensity of the work prevented excessive heat strain from developing.

Balancing ballistic protection against physiological strain: evidence from laboratory and field trials

This project was based on the premise that decisions concerning the ballistic protection provided to defence personnel should derive from an evaluation of the balance between protection level and its impact on physiological function, mobility, and operational capability. Civilians and soldiers participated in laboratory- and field-based studies in which ensembles providing five levels of ballistic protection were evaluated, each with progressive increases in protection, mass (3.4-11.0 kg), and surface-area coverage (0.25-0.52 m(2)). Physiological trials were conducted on volunteers (N = 8) in a laboratory, under hot-dry conditions simulating an urban patrol: walking at 4 km·h(-1) (90 min) and 6 km·h(-1) (30 min or to fatigue). Field-based trials were used to evaluate tactical battlefield movements (mobility) of soldiers (N = 31) under tropical conditions, and across functional tests of power, speed, agility, endurance, and balance. Finally, trials were conducted at a jungle training centre, with soldiers (N = 32) patrolling under tropical conditions (averaging 5 h). In the laboratory, work tolerance was reduced as protection increased, with deep-body temperature climbing relentlessly. However, the protective ensembles could be grouped into two equally stressful categories, each providing a different level of ballistic protection. This outcome was supported during the mobility trials, with the greatest performance decrement evident during fire and movement simulations, as the ensemble mass was increased (-2.12%·kg(-1)). The jungle patrol trials similarly supported this outcome. Therefore, although ballistic protection does increase physiological strain, this research has provided a basis on which to determine how that strain can be balanced against the mission-specific level of required personal protection.

Effects of Military Load Carriage on Susceptibility to Enemy Fire During Tactical Combat Movements.

Abstract Billing, DC, Silk, AJ, Tofari, PJ, and Hunt, AP. Effects of military load carriage on susceptibility to enemy fire during tactical combat movements. J Strength Cond Res 29(11S): S134–S138, 2015—Current military operations require soldiers to carry heavy external loads that are widely acknowledged to impair the ability to move tactically on the battlefield. However, to date, the effect of load on susceptibility to enemy fire (the probability of being hit) has not been examined. Nineteen soldiers completed a break contact simulation (five 30-m sprints commencing every 44 seconds) and a fire and movement simulation (sixteen 6-m bounds commencing every 20 seconds) in each of the 5 load conditions (ranging from 9.8 to 30.1 kg). For each simulation, the impact of load on exposure time and peak movement velocity was examined. In addition, the 6 fastest and 6 slowest soldiers (determined by exposure time in the heaviest condition) were parsed into subgroups to examine interindividual differences in response to load. Susceptibility for the 2 subgroups was modeled using exposure time for the 2 simulations and the assumed reaction time, shooting cadence, and shooting accuracy of the enemy. Susceptibility increased as a function of load for both the break contact and fire and movement simulations and became more pronounced when the participant population was parsed into fast and slow groups. When the impact of personal protection systems was isolated and analyzed, it was found that not only were the slower participants more vulnerable (as a result of not wearing the personal protection system) but also more susceptible than the faster participants who carried 11.2 kg more load. Large interindividual differences in response to external load have meaningful consequences for battlefield susceptibility, and it is therefore critical that personnel are afforded tailored training such that they maximize their proficiency in the execution of tactical combat movements.

Comparing exercise prescribed with exercise completed: Effects of gender and mode of exercise

Abstract The purpose of this study was to compare the amount of exercise prescribed with the amount completed between two different modes of training intervention and between the sexes. Thirty-two men (mean age = 39.1 years, body mass index = 32.9 kg · m−2) and women (mean age = 39.6 years, body mass index = 32.1 kg · m−2) were prescribed traditional resistance training or light-resistance circuit training for 16 weeks. Lean mass and fat mass were determined by dual-energy X-ray absorptiometry at weeks 1 and 16. A completion index was calculated to provide a measure of the extent to which participants completed exercise training relative to the amount of exercise prescribed. The absolute amount of exercise completed by the circuit training group was significantly greater than the amount prescribed (P < 0.0001). The resistance training group consistently under-completed relative to the amount prescribed, but the difference was not significant. The completion index for the circuit training group (26 ± 21.7%) was significantly different from that of the resistance training group (−7.4 ± 3.0%). The completion index was not significantly different between men and women in either group. These data suggest that overweight and obese individuals participating in light-resistance circuit training complete more exercise than is prescribed. Men and women do not differ in the extent to which they over- or under-complete prescribed exercise.