Heat Acclimation and Thermotolerance
Conditions
Keywords
Heat Acclimation, Heat Stress Test
Brief summary
The purpose of this study is to determine if five training sessions of exercise with overdressing can induce heat acclimation.
Detailed description
Twelve healthy and fit adults will complete 90 min of exercise (6.0 mph run for 30 min followed by 3.5 mph walk for 60 min) on five occasions at room temperature (\ 20 °C, 50% RH, 1 mph air velocity). Participants will be randomized into either the exercise with overdressing or exercise wearing standard physical training (PT) clothing group and complete the study in a crossover manner. Heat acclimation induction will be assessed using standardized heat stress tests (HSTs) performed before and after five training sessions. After the final HST has occurred, participants will complete a minimum 4-week washout and then return to repeat the identical protocol in the opposite configuration (overdressing vs. PT clothing). The investigators hypothesize that, compared to 5 days of exercise in PT clothing, 5 days of exercise with overdressing will lower end-exercise core temperature during standardized HSTs.
Interventions
OTHERControl
Wear normal attire (shorts/t-shirt) during exercise sessions in a gym-like environment.
OTHEROverdressing
Wear standardized overdressing ensemble during exercise sessions in a gym-like environment.
Sponsors
United States Army Research Institute of Environmental Medicine
Study design
Allocation
RANDOMIZED
Intervention model
CROSSOVER
Primary purpose
OTHER
Masking
NONE
Eligibility
Sex/Gender
ALL
Age
18 Years to 45 Years
Healthy volunteers
Yes
Inclusion criteria
* Females must be premenopausal. * Body mass index 18.5-33.0 kg m-2. * In good health as determined by the Office of Medical Support & Oversight (OMSO) General Medical Clearance. * Performs aerobic exercise at least 2 times per week and capable of running 2 miles in under 17:00 (8:30 minute mile pace). * Willing to abstain from exercise and alcoholic beverages for 24 hrs before each study visit. * Willing to abstain from caffeine for 12 hrs prior to all study visits. * Willing to abstain from food for 2 hrs prior to all study visits. * Willing to abstain from nicotine/tobacco for at least 8 hrs prior to all study visits. * Have supervisor approval if permanent party military or a federal employee at U.S. Army Natick Soldier System Center.
Exclusion criteria
* Frequent hot bath or sauna users (e.g., more than three times a week for the past month). * Females who are pregnant or planning to become pregnant during the study. * Taking dietary supplements, prescriptions, or over the counter medication, other than a contraceptive (unless approved by OMSO & PI). * Abnormal blood count during OMSO medical screening (For example: hemoglobin (Hb) outside of the typical normal values reported by LabCorp in accordance with OMSO (Normal \[Hb\] Males = 12.6-17.7 g/dL; Females = 11.1-15.9 g/dL) or hematocrit (Hct) outside of the normal ranges (Normal Hct Males = 37.5-51.0%; Females = 34.0-46.6%) levels, presence of abnormal blood chemicals (hemoglobin S or sickle cell traits). * Any history of pulmonary, cardiovascular, or renal disease (unless approved by OMSO & PI). * Uncontrolled asthma. * Current or recent respiratory tract or sinus infections (\< 2 weeks prior). * History of heat stroke or orthostatic intolerance. * Diagnosed and/or treated for fluid/electrolyte imbalance within the last 30 days. * History of obstructive disease of the gastrointestinal tract including (but not limited to) diverticulosis, diverticulitis and inflammatory bowel disease, peptic ulcer disease, Crohn's disease, ulcerative colitis. * Scheduled MRI during testing. * Allergies to adhesives (e.g., medical tape).
Design outcomes
Primary
| Measure | Time frame | Description |
|---|---|---|
| End-exercise Core Temperature | Through study completion, an average of 8 weeks | End-exercise core temperature during heat stress test |
| Resting Core Temperature | Through study completion, an average of 8 weeks | Core Temperature at Rest during Heat Stress Test |
| End-exercise heart rate | Through study completion, an average of 8 weeks | Heart rate at end of heat stress test |
| End-exercise Mean Weighted Skin Temperature | Through study completion, an average of 8 weeks | Mean weighted Skin temperature at end of heat stress test |
Secondary
| Measure | Time frame | Description |
|---|---|---|
| Urine Specific Gravity | Through study completion, an average of 8 weeks | Urine specific gravity prior to heat stress test |
Countries
United States
Outcome results
None listed