Exertional Heat Illness: Biomarkers for Prediction and Return to Duty

Inclusion Criteria: * Federal Civilian Employee, Active Duty, or DoD Beneficiary * Between the ages of 18 and 45 years * Waist circumference ≤ 39.4 inches (100 cm) * Willing to walk/run on a treadmill * Willing to undergo exposure in a thermal chamber * Willing to maintain their current activity patterns, and to abstain from alcohol, caffeine, and tobacco for 24 hours prior to all sessions * For cases who have suffered from a exertional heat illness / exertional heat stroke, must have a clinically documented heat stroke within the past year Exclusion Criteria: * History of malignant hyperthermia * Pregnant or lactating * Have overt heart disease * Have systolic blood pressure over 140 mm Hg, or diastolic pressure over 90 mm Hg * Have a waist circumference \> 39.4 inches (100 cm) * Are older than 45 or younger than 18 years of age * Are anemic * Are taking psychotropic medication for any mental health disorder * Are taking other selected medications (glucose lowering, prednisone or beta blockers)