The purpose of this study is to determine differences in physiological recovery between two consecutive days of simulated fire suppression work. The secondary purpose is to determine differences in heat gain and heat loss between two consecutive days of simulated fire suppression work. Subjects will complete two consecutive days of simulated structural firefighting shift work, 24 hours apart. Before and after each laboratory visit, subjects will continuously wear a Holter monitor and ambulatory blood pressure monitor to quantify parasympathetic tone and recovery from work.

Inclusion Criteria:

• 18-39 y old men and women
• Self-reported to be healthy

Exclusion Criteria:

• History of any cardiovascular, neurologic, renal, or metabolic disease
• Current tobacco use or regular use within the last 2 years
• Taking medications with known thermoregulatory or cardiovascular effects (e.g., aspirin, acetaminophen, ibuprofen, beta blockers, diuretics, psychotropics, etc.)
• History of exertional heat stroke
• Currently pregnant or breastfeeding, or planning to become pregnant during the study
• Inability to follow the rules of the protocols or understand the consent form
• No contraindications for ingestion of the gastrointestinal temperature pill

Individual data can be made available upon written request.