Heat Stress
Conditions
Brief 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.
Detailed 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.
Interventions
OTHERHeat acclimation
Repeated heat exposures with light exercise sufficient to elevate deep body temperature to \ 38.5C
Sponsors
Coventry University
Teesside University
University of Portsmouth
Study design
Allocation
RANDOMIZED
Intervention model
PARALLEL
Primary purpose
PREVENTION
Masking
NONE
Intervention model description
Parallel groups design
Eligibility
Sex/Gender
MALE
Age
18 Years to 45 Years
Healthy volunteers
Yes
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
Design outcomes
Primary
| Measure | Time frame | Description |
|---|---|---|
| Reduction in the peak deep body temperature | Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week) | Rectal temperature measurement during a heat stress test |
Secondary
| Measure | Time frame | Description |
|---|---|---|
| Reduction in the peak mean body temperature | Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week) | Weighted rectal and mean skin temperature measurement during a heat stress test |
| Reduction in the resting mean body temperature | Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week) | Weighted rectal and mean skin temperature measurement during a heat stress test |
| Increased plasma volume | Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week) | Change in plasma volume calculated from resting haemoglobin and haematocrit prior to a heat stress test |
| Increased sweating rate | Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week) | Sweating rate calculated from change in nude body mass and accounting for fluid consumption during a heat stress test |
| Reduced sweat sodium concentration | Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week) | Sweating sodium concentration assessed from sweat collected in a custom sweat patch on the back during a heat stress test |
| Reduced exercise heart rate | Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week) | Heart rate measured using chest telemetry during a heat stress test |
| Increased resting intracellular heat shock protein 70 content | Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week) | Assessed in peripheral blood mononuclear cells obtained before a heat stress test |
| Increased post heat stress intracellular heat shock protein 70 content | Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week) | Assessed in peripheral blood mononuclear cells obtained after a heat stress test |
| Increased resting intracellular heat shock protein 90 alpha content | Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week) | Assessed in peripheral blood mononuclear cells obtained before a heat stress tests |
| Increased post heat stress intracellular heat shock protein 90 alpha content | Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week) | Assessed in peripheral blood mononuclear cells obtained after a heat stress tests |
| Maximal oxygen uptake | Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week) | Highest rate of oxygen uptake during graded cycling exercise |
| Lactate threshold | Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week) | Power output at 4 mmol.L-1 blood lactate during graded cycling exercise |
| Gross mechanical efficiency | Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week) | Percentage ratio of external work achieved compared to the total energy expenditure during graded cycling exercise below the lactate threshold |
| Peak power output | Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week) | Highest power output achieved during exhaustive cycling exercise |
| Reduction in the resting deep body temperature | Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week) | Rectal temperature measurement during a heat stress test |
| Heart rate during exposure to hypoxia | Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week) | Assessed using chest telemetry during a hypoxic tolerance test |
| Minute ventilation during exposure to hypoxia | Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week) | Expire volume of air per minute during a hypoxic tolerance test |
| Plasma neutrophil gelatinase-associated lipocalin | Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week) | Concentration change pre to post heat stress test |
| Urine neutrophil gelatinase-associated lipocalin | Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week) | Concentration change pre to post heat stress test |
| Plasma kidney injury molecule-1 | Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week) | Concentration change pre to post heat stress test |
| Urine kidney injury molecule-1 | Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week) | Concentration change pre to post heat stress test |
| Tissue inhibitor of metalloproteinase 2 | Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week) | Urine concentration change pre to post heat stress test |
| Insulin-like growth factor-binding protein 7 | Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week) | Urine concentration change pre to post heat stress test |
| Intestinal fatty acid binding protein | Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week) | Serum concentration change pre to post heat stress test |
| Soluble cluster of differentiation 14 | Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week) | Plasma concentration change pre to post heat stress test |
| Lipopolysaccharide binding protein | Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week) | Plasma concentration change pre to post heat stress test |
| Interleukin-6 | Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week) | Plasma concentration change pre to post heat stress test |
| Cortisol | Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week) | Plasma concentration change pre to post heat stress test |
| Peripheral oxygen saturation during exposure to hypoxia | Pre heat acclimation intervention (up to 1 week) to post heat acclimation intervention (up to 1 week) | Assessed using ear or finger tip pulse oximetry during a hypoxic tolerance test |
Countries
United Kingdom
Outcome results
None listed