Trial Review

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Trial registered on ANZCTR


Registration number
ACTRN12625000811404p
Ethics application status
Submitted, not yet approved
Date submitted
10/07/2025
Date registered
29/07/2025
Date last updated
29/07/2025
Date data sharing statement initially provided
29/07/2025
Type of registration
Prospectively registered

Titles & IDs
Public title
Investigating the impact of heat stress on the gut microbiome, performance and well-being of young adults
Scientific title
Investigating the impact of heat stress on the human gut microbiota-brain axis in healthy and physically active young adults
Secondary ID [1] 314881 0
Nil
Universal Trial Number (UTN)
Trial acronym
Linked study record

Health condition
Health condition(s) or problem(s) studied:
Heat Illness 338161 0
Condition category
Condition code
Metabolic and Endocrine 334443 334443 0 0
Normal metabolism and endocrine development and function

Intervention/exposure
Study type
Interventional
Description of intervention(s) / exposure
Treatment: Other (Hot Temperature Exposure). Participants will complete 2-days (cumulative) of simulated heat exposure (40°C air temperature and 40% relative humidity (RH) with minimal air flow (<0.3 m/sec)) within La Trobe University’s environmental chamber (Bundoora campus). Participants will undertake up to 5.75 hrs (‘workday’) of heat exposure per day while performing three 75 min blocks of physical activity. The first two 75 min blocks will comprise of treadmill walking at a moderate metabolic rate (~200 Watts/m2), with 60 min passive, seated recovery between sessions. The final 75 min block will consist of 30 min treadmill walking (~200 Watts/m2), followed by 45 min treadmill jogging/running at a heavy metabolic rate (~300 Watts/m2). Up to two participants will complete the exposure at one time. La Trobe researchers will supervise and monitor all sessions. To monitor safety of participants, researchers will assess 6–20-point rating of perceived exertion scale (RPE), 13-point thermal sensation scale, and the 5-point thermal discomfort scale before the start of the ‘workday’ and every 15 minutes during the workday (including recovery during and after the exercise). Core body temperature and heart rate will also be monitored throughout.
Intervention code [1] 331483 0
Treatment: Other
Comparator / control treatment
Control treatment: Other (Ambient Temperature Exposure), Participants will complete 2-days (cumulative) of ambient temperature exposure at 20°C air temperature and 53% RH with minimal air flow (<0.3 m/sec), while undertaking ~5.75hrs of physical activity. Participants will complete the 2-day control (Ambient Temperature Exposure) first, followed by a 2-week washout period before the 2-day treatment (Hot Temperature Exposure).
Control group
Active

Outcomes
Primary outcome [1] 342142 0
Gut microbiota composition and diversity
Timepoint [1] 342142 0
Within 48hrs prior to and after control (ambient temperature) and stimulated heat stress (hot temperature) trials.
Primary outcome [2] 342143 0
Cognition (or aspects of)
Timepoint [2] 342143 0
Prior to exercise session one, immediately after second exercise session, and immediately after the final exercise session on control (ambient temperature) and stimulated heat stress (hot temperature) trial days.
Primary outcome [3] 342144 0
Body core temperature
Timepoint [3] 342144 0
Continuous during control (ambient temperature) and stimulated heat stress (hot temperature) trial days.
Secondary outcome [1] 449729 0
Self-reported questionnaires relating to mood
Timepoint [1] 449729 0
At the start and end of control (ambient temperature) and stimulated heat stress (hot temperature) trial days.
Secondary outcome [2] 449730 0
Sweat loss
Timepoint [2] 449730 0
At the start and end of control (ambient temperature) and stimulated heat stress (hot temperature) trial days.
Secondary outcome [3] 449732 0
Gait variability
Timepoint [3] 449732 0
Collected during exercise (walking/jogging) on control (ambient temperature) and stimulated heat stress (hot temperature) trial days.
Secondary outcome [4] 449733 0
Lower-limb strength and power
Timepoint [4] 449733 0
At the start and end of control (ambient temperature) and stimulated heat stress (hot temperature) trial days.
Secondary outcome [5] 449741 0
Dietary intake
Timepoint [5] 449741 0
Collected five days before and two days after first 2-day trial (ambient temperature) and five days before and two days after second 2-day trial (hot temperature).
Secondary outcome [6] 449743 0
Sleep quality
Timepoint [6] 449743 0
Collected five days before and two days after first 2-day trial (ambient temperature) and five days before and two days after second 2-day trial (hot temperature).
Secondary outcome [7] 450157 0
Self-reported questionnaires relating to mood
Timepoint [7] 450157 0
At the start and end of control (ambient temperature) and stimulated heat stress (hot temperature) trial days.
Secondary outcome [8] 450158 0
Self-reported questionnaires relating to impulsiveness
Timepoint [8] 450158 0
At the start and end of control (ambient temperature) and stimulated heat stress (hot temperature) trial days.
Secondary outcome [9] 450159 0
Self-reported questionnaires relating to gastrointestinal symptoms
Timepoint [9] 450159 0
At the start and end of control (ambient temperature) and stimulated heat stress (hot temperature) trial days.
Secondary outcome [10] 450160 0
Haemoglobin and haematocrit concentrations
Timepoint [10] 450160 0
At the start and end of control (ambient temperature) and stimulated heat stress (hot temperature) trial days.
Secondary outcome [11] 450161 0
Plasma volume (%) change
Timepoint [11] 450161 0
At the start and end of control (ambient temperature) and stimulated heat stress (hot temperature) trial days.
Secondary outcome [12] 450163 0
Inflammation
Timepoint [12] 450163 0
At the start and end of control (ambient temperature) and stimulated heat stress (hot temperature) trial days.
Secondary outcome [13] 450164 0
Metabolites (including EVs)
Timepoint [13] 450164 0
At the start and end of control (ambient temperature) and stimulated heat stress (hot temperature) trial days.
Secondary outcome [14] 450165 0
Postural stability
Timepoint [14] 450165 0
At the start and end of control (ambient temperature) and stimulated heat stress (hot temperature) trial days.
Secondary outcome [15] 450166 0
Fine motor control
Timepoint [15] 450166 0
At the start and end of control (ambient temperature) and stimulated heat stress (hot temperature) trial days.
Secondary outcome [16] 450167 0
Physical activity
Timepoint [16] 450167 0
Collected five days before and two days after first 2-day trial (ambient temperature) and five days before and two days after second 2-day trial (hot temperature).

Eligibility
Key inclusion criteria
• Male and female adult aged 18–39 years
• Non-smoker
• No pre-existing medical conditions that may interfere with the study (e.g., cardiovascular, respiratory, or metabolic disorders)
• Not on any medication that may interfere with thermoregulation, immune function, or inflammation (i.e. regular anti-inflammatory use)
• Currently engaged in regular physical activity (2-3 times per week)
Minimum age
18 Years
Maximum age
39 Years
Sex
Both males and females
Can healthy volunteers participate?
Yes
Key exclusion criteria
• BMI >30kg/m2.
• VO2max/peak below 35 ml/kg/min or above 60 ml/kg/min
• Currently pregnant or breastfeeding
• History of heat intolerance
• Severe allergies to food or environmental factors
• Diagnosed with gastrointestinal infections, diseases, or disorders
• Consumption of known modifiers of gastrointestinal integrity, such as probiotics and antibiotics within the previous 3 months.
• Consumption of nonsteroidal anti-inflammatory medications and/or stool-altering medications (e.g., laxatives, anti-diarrheal) within previous month.

Study design
Purpose of the study
Prevention
Allocation to intervention
Non-randomised trial
Procedure for enrolling a subject and allocating the treatment (allocation concealment procedures)
Methods used to generate the sequence in which subjects will be randomised (sequence generation)
Masking / blinding
Open (masking not used)
Who is / are masked / blinded?



Intervention assignment
Crossover
Other design features
Phase
Not Applicable
Type of endpoint/s
Statistical methods / analysis

Recruitment
Recruitment status
Not yet recruiting
Date of first participant enrolment
Anticipated
15/09/2025
Actual
Date of last participant enrolment
Anticipated
17/08/2026
Actual
Date of last data collection
Anticipated
25/09/2026
Actual
Sample size
Target
24
Accrual to date
Final
Recruitment in Australia
Recruitment state(s)
VIC

Funding & Sponsors
Funding source category [1] 319437 0
Government body
Name [1] 319437 0
Defence Science Institute an initiative of the State Government of Victoria
Country [1] 319437 0
Australia
Primary sponsor type
University
Name
La Trobe University
Address
Country
Australia
Secondary sponsor category [1] 321928 0
None
Name [1] 321928 0
Address [1] 321928 0
Country [1] 321928 0

Ethics approval
Ethics application status
Submitted, not yet approved
Ethics committee name [1] 318008 0
Department of Defence and Veterans’ Affairs Human Research Ethics Committee
Ethics committee address [1] 318008 0
Ethics committee country [1] 318008 0
Australia
Date submitted for ethics approval [1] 318008 0
30/06/2025
Approval date [1] 318008 0
Ethics approval number [1] 318008 0

Summary
Brief summary
Trial website
Trial related presentations / publications
Public notes

Contacts
Principal investigator
Name 142858 0
Prof Matthew Cooke
Address 142858 0
La Trobe University, Plenty Road, Bundoora, Victoria, 3086
Country 142858 0
Australia
Phone 142858 0
+61 3 94792484
Fax 142858 0
Email 142858 0
[email protected]
Contact person for public queries
Name 142859 0
Matthew Cooke
Address 142859 0
La Trobe University, Plenty Road, Bundoora, Victoria, 3086
Country 142859 0
Australia
Phone 142859 0
+61 3 94792484
Fax 142859 0
Email 142859 0
[email protected]
Contact person for scientific queries
Name 142860 0
Matthew Cooke
Address 142860 0
La Trobe University, Plenty Road, Bundoora, Victoria, 3086
Country 142860 0
Australia
Phone 142860 0
+61 3 94792484
Fax 142860 0
Email 142860 0
[email protected]

Data sharing statement
Will the study consider sharing individual participant data?
No


What supporting documents are/will be available?

No Supporting Document Provided


Results publications and other study-related documents

Documents added manually
No documents have been uploaded by study researchers.

Documents added automatically
No additional documents have been identified.