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Trial registered on ANZCTR


Registration number
ACTRN12623001069640
Ethics application status
Approved
Date submitted
31/08/2023
Date registered
6/10/2023
Date last updated
6/10/2023
Date data sharing statement initially provided
6/10/2023
Type of registration
Prospectively registered

Titles & IDs
Public title
The cumulative physiological effects of consecutive days of physical work in hot conditions
Scientific title
The cumulative physiological effects of consecutive days of physical work in hot conditions in healthy adults
Secondary ID [1] 310502 0
Nil known
Universal Trial Number (UTN)
Trial acronym
Linked study record

Health condition
Health condition(s) or problem(s) studied:
Heat stress 331298 0
Condition category
Condition code
Mental Health 328057 328057 0 0
Studies of normal psychology, cognitive function and behaviour
Neurological 328058 328058 0 0
Studies of the normal brain and nervous system
Cardiovascular 328079 328079 0 0
Normal development and function of the cardiovascular system
Musculoskeletal 328080 328080 0 0
Normal musculoskeletal and cartilage development and function

Intervention/exposure
Study type
Interventional
Description of intervention(s) / exposure
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.
Intervention code [1] 326895 0
Treatment: Other
Comparator / control treatment
Participants will perform three consecutive days of simulated work. All participants will complete the same simulated work day outlined above, albeit within a cool, air-conditioned environment (~20°C and 70% relative humidity; control) to simulate work without environmental heat stress. The 8h simulated workday will start at 08.30am and will consist of four 2h blocks. 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 (8 min) and moving a 15 kg sandbag between the ground and a 1.5 m platform at a rate of 3 reps/min (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. The participant will be directly supervised throughout by at least one member of the research team to ensure adherence to the study protocol.
Control group
Active

Outcomes
Primary outcome [1] 335927 0
Body core temperature, as assessed using an ingestible pill thermometer (BodyCap, e-Celsius Performance, France).
Timepoint [1] 335927 0
E nd of each 8-h simulated work day (immediately at the end of the final 2 h work block) on days one, two and three.
Secondary outcome [1] 426164 0
Whole-body strength will be assessed using the mid-thigh pull, the participant will pull on a fixed barbell with a maximal effort, with force (Newtons) measured with a force plate (Fitness Technology 400S Performance Force Plate, Fullarton, SA, Australia) underneath the participant.
Timepoint [1] 426164 0
End of each 8-h simulated work day (immediately at the end of the final 2 h work block) on days one, two and three.
Secondary outcome [2] 426223 0
Heart rate (beats/min), as assessed using the Polar Team2 System (Polar Electro Oy, Kempele, Finland).
Timepoint [2] 426223 0
End of each 8-h simulated work day (immediately at the end of the final 2 h work block) on days one, two and three.
Secondary outcome [3] 426224 0
Skin temperature will be measured at 4 sites (arm, chest, thigh, calf) using iButtons (DS1921 G-F5 Thermochron, iButtonLink LLC, WI, USA) fixed to the skin with medical tape. Mean skin temperature will be approximated from the four local skin temperatures (arm: 30%, chest: 30%, thigh: 20%, calf: 20%).
Timepoint [3] 426224 0
End of each 8-h simulated work day (immediately at the end of the final 2 h work block) on days one, two and three.
Secondary outcome [4] 426225 0
Sweat loss (kg) from the start to end of each 8-h simulated work day, as assessed by the change in body mass measured with digital weighing scales (corrected for fluid and food consumption and urine production).
Timepoint [4] 426225 0
End of each 8-h simulated work day (immediately at the end of the final 2 h work block) on days one, two and three.
Secondary outcome [5] 426226 0
Venous blood will be collected at the start and end of each 8-h simulated work day via venepuncture into K2EDTA 5.4 mg BD Vacutainer® tubes (BD, Franklin Lakes, NJ, USA) and used to measure haemoglobin and haematocrit concentrations (HemoCue AB, Ängelholm, Sweden) to determine the change (%) in plasma volume (Dill and Costill method).
Timepoint [5] 426226 0
End of each 8-h simulated work day (immediately at the end of the final 2 h work block) on days one, two and three.
Secondary outcome [6] 426227 0
Neurobehavioural testing will be conducted at the start and end of each 8-h simulated workday using the automated 'Cognition' test battery from Joggle Research (Joggle Research, Seattle, WA), presented to participants on an electronic tablet (Apple iPad Air, Cupertino, CA, USA),
Timepoint [6] 426227 0
End of each 8-h simulated work day (immediately at the end of the final 2 h work block) on days one, two and three.
Secondary outcome [7] 427609 0
Grip strength will be assessed with a hand-grip dynamometer, as the maximum force (Newtons) produced.
Timepoint [7] 427609 0
End of each 8-h simulated work day (immediately at the end of the final 2 h work block) on days one, two and three.
Secondary outcome [8] 427610 0
Vertical jump performance (strength and power) will be assessed with a force plate as the flight time (seconds) during a maximal vertical jump.
Timepoint [8] 427610 0
End of each 8-h simulated work day (immediately at the end of the final 2 h work block) on days one, two and three.
Secondary outcome [9] 427611 0
Medicine ball throw (strength and power) will be measured as the maximal distance (m) that the participant can throw a 5 kg medicine ball from the seated position.
Timepoint [9] 427611 0
End of each 8-h simulated work day (immediately at the end of the final 2 h work block) on days one, two and three.

Eligibility
Key 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.
Minimum age
18 Years
Maximum age
40 Years
Sex
Both males and females
Can healthy volunteers participate?
Yes
Key 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.

Study design
Purpose of the study
Prevention
Allocation to intervention
Randomised controlled trial
Procedure for enrolling a subject and allocating the treatment (allocation concealment procedures)
Sealed opaque envelopes
Methods used to generate the sequence in which subjects will be randomised (sequence generation)
Permuted block randomization with stratification for gender
Masking / blinding
Who is / are masked / blinded?



Intervention assignment
Parallel
Other design features
Phase
Not Applicable
Type of endpoint/s
Statistical methods / analysis
Data will be analysed using linear mixed models (LMM) to determine the influence of the hot and humid condition on all dependent variables.

Recruitment
Recruitment status
Not yet recruiting
Date of first participant enrolment
Anticipated
9/10/2023
Actual
Date of last participant enrolment
Anticipated
2/12/2024
Actual
Date of last data collection
Anticipated
20/12/2024
Actual
Sample size
Target
32
Accrual to date
Final
Recruitment in Australia
Recruitment state(s)
VIC
Recruitment postcode(s) [1] 41286 0
3125 - Burwood

Funding & Sponsors
Funding source category [1] 314561 0
Government body
Name [1] 314561 0
Department of Defence
Country [1] 314561 0
Australia
Funding source category [2] 314721 0
University
Name [2] 314721 0
Deakin University
Country [2] 314721 0
Australia
Primary sponsor type
University
Name
Deakin University
Address
221 Burwood HighwayBurwood, VIC, 3125
Country
Australia
Secondary sponsor category [1] 316677 0
None
Name [1] 316677 0
Address [1] 316677 0
Country [1] 316677 0

Ethics approval
Ethics application status
Approved
Ethics committee name [1] 313598 0
Deakin University Human Research Ethics Committee
Ethics committee address [1] 313598 0
Human Research EthicsDeakin Research IntegrityDeakin University221 Burwood HighwayBurwoodVIC, 3125
Ethics committee country [1] 313598 0
Australia
Date submitted for ethics approval [1] 313598 0
24/03/2023
Approval date [1] 313598 0
12/07/2023
Ethics approval number [1] 313598 0
DUHREC: 2023-081

Summary
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.
Trial website
Trial related presentations / publications
Public notes

Contacts
Principal investigator
Name 128698 0
A/Prof Luana Main
Address 128698 0
Deakin University, Melbourne Burwood Campus, 221 Burwood Highway, Burwood VIC 3125
Country 128698 0
Australia
Phone 128698 0
+61 3 9244 5030
Fax 128698 0
Email 128698 0
[email protected]
Contact person for public queries
Name 128699 0
Luana Main
Address 128699 0
Deakin University, Melbourne Burwood Campus, 221 Burwood Highway, Burwood VIC 3125
Country 128699 0
Australia
Phone 128699 0
+61 3 9244 5030
Fax 128699 0
Email 128699 0
[email protected]
Contact person for scientific queries
Name 128700 0
Luana Main
Address 128700 0
Deakin University, Melbourne Burwood Campus, 221 Burwood Highway, Burwood VIC 3125
Country 128700 0
Australia
Phone 128700 0
+61 3 9244 5030
Fax 128700 0
Email 128700 0
[email protected]

Data sharing statement
Will individual participant data (IPD) for this trial be available (including data dictionaries)?
Yes
What data in particular will be shared?
De-identified individual participant data that underlie the results.
When will data be available (start and end dates)?
Immediately following publication to 5 years following publication
Available to whom?
Researchers who provide a methodological sound proposal
Available for what types of analyses?
To achieve aims in the approved proposal
How or where can data be obtained?
De-identified individual participant data are available from the corresponding author ([email protected]) upon reasonable request.


What supporting documents are/will be available?

Doc. No.TypeCitationLinkEmailOther DetailsAttachment
20181Study protocol  [email protected]
20182Informed consent form  [email protected]
20200Ethical approval  [email protected]



Results publications and other study-related documents

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