The purpose of this study is to determine if exercise with extra clothing in a gym-like environment can increase body temperatures appropriately to help people adapt to the heat.

The purpose of the present study is to examine the influence of a novel 90-minute exercise + overdressing protocol on thermal responses in comparison to matched exercise in standard PT clothing. Sixteen healthy and fit adults (8 men and 8 women) will complete two 90-minute exercise sessions (randomized order) in a temperate environment (~20°C, ~50% relative humidity, and ~1 mph air velocity) involving a 30-minute run immediately followed by a 60-minute walk. Participants will wear standard physical training (PT) clothing (shorts, t-shirt) during one session and an overdressing ensemble in the other. The investigators hypothesize that 1) exercise + overdressing will elevate core temperature to between 38.3°C and 39.3°C for at least 45 minutes; and 2) elevations in core temperature, skin temperature, heart rate, and sweat rate will be substantially larger than observed with 90 minutes of matched exercise in standard PT clothing.

Inclusion Criteria:

• Male or female, age 18-45
• Females must be premenopausal
• Body mass index 18.5-30.0 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 16:00 (8 minute mile pace)
• Willing to abstain from exercise and alcoholic beverages for 24 hours before each study visit.
• Willing to abstain from caffeine for 12 hours prior to all study visits.
• Willing to abstain from food for 2 hours prior to all study visits.
• Willing to abstain from nicotine/tobacco for at least 8 hours 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:

• 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 or cardiovascular disease
• Any history of asthma
• Current or recent respiratory tract or sinus infections (< 1 month prior)
• History of heat intolerance 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).