In cold weather environments, blood flow to the extremities is significantly reduced, which severely impairs hand function and induces thermal discomfort. Prolonged or repeated cold exposure elicits an adaptive habituation response that is characterized by blunted skin vasoconstriction and thus may be an effective strategy to improve peripheral perfusion, reduce thermal discomfort, and maintain hand function during cold weather military operations. Since mission conditions often involve low ambient temperatures, countermeasures that reduce cold-induced decrements in hand function and thermal comfort are important to enhance Warfighter readiness in cold weather battlefield environments. The goals of this study are to 1) evaluate the effectiveness of cold habituation in improving skin blood flow, hand function, and thermal comfort during cold exposure and 2) identify the mechanisms that contribute to improvements in skin blood flow following habituation.

Participants (n=15, 18-39 yrs) will complete a preliminary cold air exposure (baseline testing) followed by 8 days of repeated cold air exposures with minimal clothing. The cold exposures will be 2 hours in duration and will be conducted in 8°C (46°F) conditions. Before and after the repeated cold exposures, participants will undergo hand function tests, assessments of thermal comfort, and skin blood flow testing.

Inclusion Criteria:

• Male or female, age 18-39
• In good health as determined by OMSO (Office of Medical Support and Oversight)
• Willing to refrain from exercise and caffeinated or alcoholic beverages for 12 hours before each testing session
• Willing to refrain from smoking or tobacco use 8 hours before each testing session

Exclusion Criteria:

• History of cold injuries of any severity (e.g., frostbite, trench foot, chilblains).
• Raynaud's syndrome.
• Cold-induced asthma/bronchospasm
• Previous hand/finger injuries that impair dexterity and hand function.
• Metal hardware (plates/screws) in the forearms and hands.
• Current use of medications or dietary supplements that could alter cardiovascular, thermoregulatory, or vascular control (e.g., anti-hypertensives, statins).
• Known allergies to medical adhesives.
• Heart, lung, kidney, muscle, or nerve disorder(s)
• A planned MRI during the study or within 2 days after completing a cold test.
• Women who are pregnant, planning to become pregnant, or breastfeeding.
• Not willing to have small areas of skin on the body shaved (if deemed necessary for attachment of study instrumentation)