Comparison of a Novel Condensed Heat Acclimation Programme With a Traditional Longer-term Heat Acclimation Programme

Heat Stress Clinical Trial

Official title:

Comparison of a Novel Condensed Heat Acclimation Programme With a Traditional Longer-term Heat Acclimation Programme

Clinical Trial Details — Status: Completed

Administrative data

• NCT number: NCT05600452
• Other study ID #: 1017/MoDREC/19
• Status: Completed
• Phase: N/A
• Start date: January 17, 2020
• Est. completion date: January 4, 2023

Study information

• Verified date: December 2023
• Source: University of Portsmouth
• Contact: n/a
• Is FDA regulated: No
• Study type: Interventional

Clinical Trial Summary

Repeated exposure to heat in a laboratory setting (acclimation) elicits a range of adaptations, which reduce heat illness risk and increase work capacity in the heat. Traditional approaches to heat acclimation require daily heat exposures of 1 to 2 hours over ~7 to 10 consecutive days. Heat acclimation approaches which reduce the number of days to achieve acclimation may have utility. The primary purpose of the proposed research is to determine whether it is possible to achieve a similar degree of heat acclimation to that seen with a traditional longer-term heat acclimation approach by increasing the frequency of heat exposure, utilising multiple daily heat exposures over a smaller number of days. Secondary aims of the research are to examine whether heat acclimation provides cross-adaptation to a hypoxic stressor and whether heat acclimation improves aerobic fitness.

Description:

Individuals are often required to operate in adverse conditions and may be exposed to prolonged periods of high ambient heat and humidity. High environmental temperatures impair work capacity and increase heat-illness risk. Repeated exposure to heat in a laboratory setting (acclimation) elicits a range of adaptations, which reduce heat illness risk and increase work capacity in the heat. However, traditional approaches to heat acclimation are time consuming, typically requiring daily heat exposures of 1 to 2 hours over ~7 to 10 consecutive days. This can be logistically difficult to implement and impractical, particularly in situations where an individual must be rapidly deployed. Therefore, heat acclimation approaches which reduce the number of days to achieve acclimation may have utility. In addition, recent research studies have suggested that adaptation to heat may improve tolerance to hypoxia (cross-adaptation) and improve aerobic fitness; these effects may also be beneficial in a military context. Therefore, the primary purpose of the proposed research is to determine whether it is possible to achieve a similar degree of heat acclimation to that seen with a traditional longer-term heat acclimation approach by increasing the frequency of heat exposure, utilising multiple daily heat exposures over a smaller number of days. Secondary aims of the research are to examine whether heat acclimation provides cross-adaptation to a hypoxic stressor and whether heat acclimation improves aerobic fitness. Heat acclimation will be evaluated using a range of whole-body (cardiovascular, thermoregulatory, psychophysiological) and biochemical markers.

Recruitment information / eligibility

• Status: Completed
• Enrollment: 37
• Est. completion date: January 4, 2023
• Est. primary completion date: January 4, 2023
• Accepts healthy volunteers: Accepts Healthy Volunteers
• Gender: Male
• Age group: 18 Years to 45 Years

Eligibility

Inclusion Criteria:

• Male

• Physically active and healthy as determined by pre-participation health screening questionnaire.

• Free of COVID-19 symptoms (loss or change in sense of smell or taste, fever and new, continuous cough) as determined by pre-screening questionnaire.

• Resting diastolic blood pressure between 60 and 90 mmHg; resting systolic blood pressure between 90 and 150 mmHg A resting ECG is required if: individuals are over 30 years of age; they are unfamiliar with exercise of a maximal nature; they have a family history of adverse cardiac events. The ECG is to be reviewed by the Independent Medical Officer.

Exclusion Criteria:

• Current smokers

• Recent (< 3 months) participation in a formal heat acclimation regimen, or regular frequent heat exposures that may render the participant partially heat acclimated (other than regular exercise)

• Recent (< 3 months) high altitude (>1 500m ) sojourn that may render the participant partially altitude acclimated

• Diagnosed cardiovascular, metabolic or respiratory conditions (excluding asthma)

• Prior history of heat illness

• Prior history of collapse or intolerance with exposure to altitude

• Recent blood donation (within 3 months of commencing study)

• Baseline serum sodium level <135 mmol.L-1

• Any other extant medical condition which may be exacerbated by participation

• Participants with inadequate understanding of English.

• Any volunteers who are currently participating in any other research studies which may influence their responses or the results obtained

Related Conditions & MeSH terms

• Heat Stress
• Heat Stress Disorders

Intervention

Other:
• Heat acclimation
Repeated heat exposures with light exercise sufficient to elevate deep body temperature to ~ 38.5C

Locations

Country	Name	City	State
United Kingdom	University of Portsmouth	Portsmouth	Hampshire

Sponsors (3)

Lead Sponsor	Collaborator
University of Portsmouth	Coventry University, Teesside University

Country where clinical trial is conducted

United Kingdom, 

Outcome

Type	Measure	Description	Time frame	Safety issue
Primary	Reduction in the peak deep body temperature	Rectal temperature measurement during a heat stress test	Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week)
Secondary	Reduction in the resting deep body temperature	Rectal temperature measurement during a heat stress test	Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week)
Secondary	Reduction in the peak mean body temperature	Weighted rectal and mean skin temperature measurement during a heat stress test	Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week)
Secondary	Reduction in the resting mean body temperature	Weighted rectal and mean skin temperature measurement during a heat stress test	Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week)
Secondary	Increased plasma volume	Change in plasma volume calculated from resting haemoglobin and haematocrit prior to a heat stress test	Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week)
Secondary	Increased sweating rate	Sweating rate calculated from change in nude body mass and accounting for fluid consumption during a heat stress test	Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week)
Secondary	Reduced sweat sodium concentration	Sweating sodium concentration assessed from sweat collected in a custom sweat patch on the back during a heat stress test	Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week)
Secondary	Reduced exercise heart rate	Heart rate measured using chest telemetry during a heat stress test	Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week)
Secondary	Increased resting intracellular heat shock protein 70 content	Assessed in peripheral blood mononuclear cells obtained before a heat stress test	Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week)
Secondary	Increased post heat stress intracellular heat shock protein 70 content	Assessed in peripheral blood mononuclear cells obtained after a heat stress test	Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week)
Secondary	Increased resting intracellular heat shock protein 90 alpha content	Assessed in peripheral blood mononuclear cells obtained before a heat stress tests	Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week)
Secondary	Increased post heat stress intracellular heat shock protein 90 alpha content	Assessed in peripheral blood mononuclear cells obtained after a heat stress tests	Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week)
Secondary	Maximal oxygen uptake	Highest rate of oxygen uptake during graded cycling exercise	Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week)
Secondary	Lactate threshold	Power output at 4 mmol.L-1 blood lactate during graded cycling exercise	Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week)
Secondary	Gross mechanical efficiency	Percentage ratio of external work achieved compared to the total energy expenditure during graded cycling exercise below the lactate threshold	Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week)
Secondary	Peak power output	Highest power output achieved during exhaustive cycling exercise	Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week)
Secondary	Peripheral oxygen saturation during exposure to hypoxia	Assessed using ear or finger tip pulse oximetry during a hypoxic tolerance test	Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week)
Secondary	Heart rate during exposure to hypoxia	Assessed using chest telemetry during a hypoxic tolerance test	Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week)
Secondary	Minute ventilation during exposure to hypoxia	Expire volume of air per minute during a hypoxic tolerance test	Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week)
Secondary	Plasma neutrophil gelatinase-associated lipocalin	Concentration change pre to post heat stress test	Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week)
Secondary	Urine neutrophil gelatinase-associated lipocalin	Concentration change pre to post heat stress test	Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week)
Secondary	Plasma kidney injury molecule-1	Concentration change pre to post heat stress test	Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week)
Secondary	Urine kidney injury molecule-1	Concentration change pre to post heat stress test	Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week)
Secondary	Tissue inhibitor of metalloproteinase 2	Urine concentration change pre to post heat stress test	Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week)
Secondary	Insulin-like growth factor-binding protein 7	Urine concentration change pre to post heat stress test	Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week)
Secondary	Intestinal fatty acid binding protein	Serum concentration change pre to post heat stress test	Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week)
Secondary	Soluble cluster of differentiation 14	Plasma concentration change pre to post heat stress test	Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week)
Secondary	Lipopolysaccharide binding protein	Plasma concentration change pre to post heat stress test	Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week)
Secondary	Interleukin-6	Plasma concentration change pre to post heat stress test	Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week)
Secondary	Cortisol	Plasma concentration change pre to post heat stress test	Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week)