None listed
Conditions
Brief summary
Many trades (e.g. infantry, special operations) within the Australian Army require individuals to perform consecutive days of prolonged (>10 h), physically demanding work in the heat, as part of multi-day training exercises and operations. These conditions can cause dangerous rises in body core temperature, cardiovascular strain and fluid depletion over the course of the day, which can cause carry-over effects that may exacerbate exertional heat illness (EHI) risk on the following day. For example, recent epidemiological data from the US Armed forces indicate that the odds of developing EHI on a given day is exacerbated when training is conducted in hot weather on the preceding day. Further, several field- and laboratory-based studies have demonstrated that this elevated EHI risk may be related to exacerbated increases in body core temperature and cardiovascular strain on the second of consecutive days of work in the heat. While the mechanism(s) explaining these impairments in thermoregulatory and cardiovascular strain remain unclear, there is recent evidence to indicate that these carry-over effects may progressively worsen over two or more days. Despite the potentially deleterious effects of multi-day exercise in the heat on physiological strain, there are major gaps in our understanding of the factors (e.g. aerobic fitness, environment, work intensity) that may exacerbate the magnitude of these effects. For example, recent work has demonstrated that increasing age may worsen the next-day effects of a prolonged workday in the heat on thermoregulatory function. There also exists shortcomings in our knowledge of the impact of multi-day exercises in the heat on cognitive function and fatigue, which may reduce task performance and increase the risk of errors and risk taking behaviour. This makes it difficult to develop interventions to mitigate risk of decrements in performance and improve safety. The overarching aim of this project is to investigate the cumulative physiological effects of consecutive days of physical work in hot conditions.
Interventions
Participants will perform three consecutive days of simulated work. Each simulated workday will start at 08.30am and will consist of four 2h blocks (8 h total). Each 2h block will comprise of two 30 min bouts of work, each followed by 30 min seated rest (i.e. a work-to-rest cycle of 30 min rest, 30 min work). The 30 min work bouts will involve 15 min of treadmill walking (4.5 km/h, 5% grade) followed by 15 min of manual handling, which will comprise lifting and carrying a 15-kg sand bag for 4 m
Participants will perform three consecutive days of simulated work. Each simulated workday will start at 08.30am and will consist of four 2h blocks (8 h total). Each 2h block will comprise of two 30 min bouts of work, each followed by 30 min seated rest (i.e. a work-to-rest cycle of 30 min rest, 30 min work). The 30 min work bouts will involve 15 min of treadmill walking (4.5 km/h, 5% grade) followed by 15 min of manual handling, which will comprise lifting and carrying a 15-kg sand bag for 4 m at a rate of 3 reps/min (for 8 min) and then moving a 15 kg sandbag between the ground and a 1.5 m platform at a rate of 3 reps/min (for 7 min). During each rest period, participants will have the opportunity to use the toilet and consume water and a self-provided lunch and snacks as desired. All participants will complete the simulated workday within a hot-humid environment (35°C and 63% relative humidity; treatment [hot]). The hot-humid environment has been informed by the climate statistics from Darwin Airport, Northern Territory during February to simulate the conditions experienced by personnel deployed to this environment. The participant will be directly supervised throughout by at least one member of the research team to ensure adherence to the study protocol.
Sponsors
Deakin University
Study design
Allocation
Randomised controlled trial
Intervention model
Crossover
Primary purpose
Prevention
Eligibility
Sex/Gender
All
Age
18 Years to 40 Years
Healthy volunteers
Yes
Inclusion criteria
Participants will be physically active males and females ages 18 – 40 years and BMI <35 kg/m2 as this is a representative sample of military personnel completing physically demanding workloads in the hot humid environments. Prospective participants will complete a pre-assessment screening to confirm eligibility for inclusion. This will involve a DEXA scan and an aerobic and strength assessment to determine if they meet the minimum entry fitness standards for the Australian Army (i.e., equivalent to a multi-stage shuttle run result = 6.1; 2 min maximum push ups = 4 for females, 8 for males; 2 min maximum sit ups = 20). These age range, BMI and physical fitness levels have been selected to ensure that participants are healthy and physically capable of completing the protocol.
Exclusion criteria
Chronic disease Pregnant or lactating a current/habitual user of psychoactive drugs. working night shifts/irregular working schedules. Participants with diagnosed mental illness and muscle, bone, joint and tissue related injures will be excluded from the study if it impairs their ability to complete the protocol or may provide further harm to their diagnosed condition. Participants will be screened using the ESSA’s Adult Pre-exercise Screening System (APSS) and be asked the following “Have you been diagnosed with any mental health conditions that may impair your ability to complete the study’s protocol or which may negatively impact your health and well-being by participating in this study?”. Participants will be required to be fluent in English due to the verbal and written procedures a part of the research protocol.
Outcome results
None listed