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Trial registered on ANZCTR

Registration number
Ethics application status
Date submitted
Date registered
Date last updated
Date data sharing statement initially provided
Type of registration
Prospectively registered

Titles & IDs
Public title
Investigating heat tolerance in females
Scientific title
Investigating heat tolerance in females
Secondary ID [1] 297248 0
Universal Trial Number (UTN)
Trial acronym
Linked study record

Health condition
Health condition(s) or problem(s) studied:
Heat illness 311320 0
Condition category
Condition code
Injuries and Accidents 313136 313136 0 0
Other injuries and accidents

Study type
Patient registry
Target follow-up duration
Target follow-up type
Description of intervention(s) / exposure
The exposure variable in this study is exertional heat stroke (EHS) which is characterized by an elevated internal body temperature above 40°C accompanied by dysfunction or disturbance of the central nervous system.

As part of the return to duty process, the Australian Defence Force recommends that all Australian Defence Force members who have experienced exertional heat stroke are sent for a heat tolerance test. The heat tolerance test is a standard procedure that is performed for all cases of heat stroke to determine their heat tolerance status.

Study participants will be grouped into cases and an unexposed (control) group.

The exposed group (cases) will be female Defence Force members who have been referred to the chief investigator for heat tolerance testing as part of the routine procedure following a heat stroke event.

The unexposed group will be female participants recruited from the general community who have no history of heat illness.

Using the standard heat tolerance test the heat tolerance responses of both the cases and controls will be observed to identify their heat tolerance status (heat tolerant or intolerant). The standard heat tolerance test comprises treadmill walking for 2 hours at 5 km/h and a 2% grade in a climate control chamber set to hot/dry conditions (40°C, 40% relative humidity). The key outcome variables that will be assessed during the 2 hour test will include core temperature, heart rate, skin temperature, sweat rate, and subjective ratings of thermal sensation and thermal comfort. The HTT involves a total of 3.5-4 hours observation.

All participants will also undertake a VO2max test to assess aerobic fitness. Assessment of aerobic fitness will enable us to establish whether the control group is a suitable comparator for the cases as aerobic fitness is known to affect heat tolerance. VO2 will be measured using a metabolic cart and either treadmill or cycle ergometer. The participants will commence the max test at a low intensity to warm up. The exercise intensity will then be progressively increased until the participants reach a point of voluntary exhaustion. This test usually involves 8-15 minutes of exercise and a total of 30-45 mins of total time. The VO2max test can occur within a 4 week period of the heat tolerance test, either beforehand or afterwards.

Alternative heat tolerance test protocol
The current HTT will be considered inappropriate for females if a large proportion of the controls are categorized as heat intolerant (false positive). If the protocol is appropriate, most if not all the control participants should pass the HTT. However, previous studies have shown that a higher proportion of women were classified as heat intolerant using the HTT compared to men.
If the protocol is not valid for females, then the participants will be asked to attend the laboratory on a second occasion to repeat the test with a lower workload. A modified protocol will then be developed.
Intervention code [1] 313503 0
Diagnosis / Prognosis
Comparator / control treatment
The comparator group will include females with no history of heat illness. They will undertake the same standard heat tolerance test protocol as the cases. The criteria used to determine heat intolerance are (a) Tc exceeding 38.6°C, or (b) HR exceeding 160 beats/min, (c) failure of Tc or HR to stabilise during the test or (d) failure to complete the 120 min walk. Heat tolerance responses will be compared between the cases and controls.
Control group

Primary outcome [1] 318870 0
Heat tolerance status (either heat tolerant or heat intolerant) assessed using the standard heat tolerance test.
Timepoint [1] 318870 0
Immediately after completing the standard heat tolerance test.
Secondary outcome [1] 366293 0
Aeobic fitness (is a composite outcome that includes VO2 max, heart rate and subjective rating)

VO2 max test will be conducted using a metabolic cart and either a cycle ergometer (ramp protocol) or treadmill (step protocol commencing at light jogging speed). A mouthpiece for the metabolic cart will be placed in the subject’s mouth and held in place by adjusting the headpiece. A nose clip will be placed on the nose to ensure mouth breathing only. This ensures that all oxygen consumed, and carbon dioxide produced will be measured by the metabolic cart. Heart rate and subjective ratings of effort will be obtained during the test along with the VO2max (maximum oxygen consumed). Heart rate and subjective ratings are used to verify that VO2max is reached during the test.
Timepoint [1] 366293 0
The aerobic fitness will be assessed once within 4 weeks of the heat tolerance test.

Key inclusion criteria
Cases will include female Australian Defence Force members referred to the primary investigator for heat tolerance testing following a known or suspected case of heat stroke or who have previously been referred by their physician for heat tolerance testing. Controls will be female volunteers (civilians) from the general community who have never had a history of heat illness.
Minimum age
18 Years
Maximum age
50 Years
Can healthy volunteers participate?
Key exclusion criteria
Potential participants who have any of the following criteria will be excluded from the study:
- Male
- Pregnant or lactating women in the Defence Force or in the general community
- Medical conditions that predisposes and increases the risk of heat stroke
- History of hypertension, malignant hyperthermia, and diabetes
- Currently being treated for any mental disorder which affects their ability to comprehend the study details and therefore their ability to provide consent
- Currently being treated for anaemia
- Currently using glucose lowering agents, prednisone, or beta blockers

Study design
Natural history
Case control
Statistical methods / analysis
A priori power analysis was computed using G-power to determine the sample size. The power analysis indicated that a total of 34 (17 cases and 17 controls) participants are needed to have 80% power for detecting a medium sized effect with a statistical significance criterion level of 0.05. However, the number of control participants will be increased to approximately 30 to increase the power of the study.

Alternative heat tolerance test protocol
The current HTT will be considered inappropriate for females if 10% of the controls are categorized as heat intolerant. If this is the case, the test parameters (treadmill speed and/or grade) will be modified to develop a more appropriate protocol for females.

The statistical analysis will be conducted using SPSS (version 24) and SAS Inst., Cary, NC statistical software. The level of significance will be set at 0.05. The analysis will include comparing the test outcomes for the cases and the controls. An independent sample T test or Man-Whitney U test (based on the normality of the data) will be used to compare the mean/median difference in heart rate and core temperature of the cases and controls. In addition, mathematical modelling to analyse the patterns of the rise in core temperature will be conducted.

Recruitment status
Not yet recruiting
Date of first participant enrolment
Date of last participant enrolment
Date of last data collection
Sample size
Accrual to date
Recruitment in Australia
Recruitment state(s)

Funding & Sponsors
Funding source category [1] 301809 0
Name [1] 301809 0
Researcher consultancy funds
Address [1] 301809 0
College of Healthcare Sciences, James Cook University, 1 James Cook Drive, Douglas QLD 4814
Country [1] 301809 0
Primary sponsor type
James Cook University
1, James Cook Drive, Douglas QLD 4814
Secondary sponsor category [1] 301552 0
Name [1] 301552 0
Address [1] 301552 0
Country [1] 301552 0

Ethics approval
Ethics application status
Ethics committee name [1] 302515 0
Departments of Defence and Veterans' Affairs Human Research Ethics Committee (DDVA HREC)
Ethics committee address [1] 302515 0
CP3-7-038, Campbell Park Offices, PO Box 7912, Canberra BC ACT 2610
Ethics committee country [1] 302515 0
Date submitted for ethics approval [1] 302515 0
Approval date [1] 302515 0
Ethics approval number [1] 302515 0

Brief summary
Heat tolerance testing is used to establish if a Defence member is fit for return to duty following heat illness. The most frequently utilized heat tolerance test was developed by the Israeli Defence Force in the late 1970s with male participants. To our knowledge, the appropriateness of this protocol for females has not yet been established. Therefore, this study aims to investigate female heat tolerance responses using the current standard heat tolerance test protocol and to develop an alternative protocol if the current protocol is inappropriate.
Trial website
Trial related presentations / publications
Public notes
We will recruit cases Australia wide, while the controls will be recruited from Queensland.

Principal investigator
Name 90482 0
Dr Melissa Crowe
Address 90482 0
Division of Tropical Health and Medicine, James Cook University, 1, James Cook Drive, Douglas QLD 4814
Country 90482 0
Phone 90482 0
+61 7 478 15610
Fax 90482 0
Email 90482 0
Contact person for public queries
Name 90483 0
Dr Melissa Crowe
Address 90483 0
Division of Tropical Health and Medicine, James Cook University, 1, James Cook Drive, Douglas QLD 4814
Country 90483 0
Phone 90483 0
+61 7 478 15610
Fax 90483 0
Email 90483 0
Contact person for scientific queries
Name 90484 0
Dr Melissa Crowe
Address 90484 0
Division of Tropical Health and Medicine, James Cook University, 1, James Cook Drive, Douglas QLD 4814
Country 90484 0
Phone 90484 0
+61 7 478 15610
Fax 90484 0
Email 90484 0

Data sharing statement
Will individual participant data (IPD) for this trial be available (including data dictionaries)?
No/undecided IPD sharing reason/comment
For ethical reasons, the individual participant data will not be shared. The population being studied is likely to be small, therefore if the individual data is made available there is a risk that the participants may be identified.
What supporting documents are/will be available?
Informed consent form
Ethical approval
How or where can supporting documents be obtained?
Type [1] 1246 0
Ethical approval
Citation [1] 1246 0
Link [1] 1246 0
Email [1] 1246 0
Other [1] 1246 0
Type [2] 1377 0
Informed consent form
Citation [2] 1377 0
Link [2] 1377 0
Email [2] 1377 0
Other [2] 1377 0
Informed consent from for cases
Type [3] 1378 0
Informed consent form
Citation [3] 1378 0
Link [3] 1378 0
Email [3] 1378 0
Other [3] 1378 0
Informed consent form for controls
Summary results
No Results