Heat Therapy During Reduced Physical Activity

Inclusion Criteria: * Adults aged 18 years or older * Healthy men and premenopausal women * Able and willing to provide written informed consent * Able to perform knee-extension cycling exercise * Stable habitual physical activity for at least 3 months before enrollment * Pass the American College of Sports Medicine (ACSM) Preparticipation Health Screening * Not currently taking medications known to affect cardiovascular function (e.g., antihypertensive medications or beta-blockers) * No regular sauna or hot-tub use (fewer than six exposures during the previous 2 months) * Willing and able to comply with all study procedures, including temporary reduction of physical activity, daily sauna visits, physiological testing, and follow-up assessments Exclusion Criteria: * Younger than 18 years of age * Failure to pass the ACSM Preparticipation Health Screening * Unable or unwilling to perform exercise testing * Current cigarette or marijuana use * Pregnant or planning to become pregnant during the study * History or current diagnosis of cardiovascular disease, metabolic disease, or cognitive impairment * Use of medications known to influence cardiovascular function or exercise tolerance (e.g., antihypertensive medications or beta-blockers) * Regular sauna or hot-tub use (six or more exposures during the previous 2 months) * History of heat-related illness * Any condition that, in the opinion of the investigators, would interfere with safe participation or interpretation of study results * Inability to understand the study procedures or provide informed consent