Superficial shell insulation in resting and exercising men in cold water

Area of Science:

• Human Physiology
• Thermoregulation
• Environmental Medicine

Background:

• Understanding human thermal insulation is crucial for predicting physiological responses to cold environments.
• The superficial shell (skin and subcutaneous fat) is a primary barrier against heat loss, but its insulation capacity varies.
• The role of different body tissues in overall thermal insulation during cold exposure requires further elucidation.

Purpose of the Study:

• To quantify the superficial shell insulation (Iss) of the thigh in male subjects exposed to varying water temperatures.
• To determine the relationship between superficial shell insulation and tissue thickness.
• To assess the impact of mild leg exercise on superficial shell insulation and overall tissue insulation (It).

Main Methods:

• Measurements of subcutaneous fat temperature, skin surface temperature, and skin heat flux were used to calculate thigh superficial shell insulation (Iss).
• Overall maximal tissue insulation (It,max) was calculated during rest in critical water temperature (CWT) using rectal temperature, water temperature, metabolic rate, and body heat changes.
• Thigh Iss and overall It were measured during mild leg cycling exercise in CWT.

Main Results:

• Thigh superficial shell insulation (Iss) increased with tissue thickness and reached maximal values (Iss,max) at or below critical water temperature (CWT).
• Iss,max was linearly related to thigh fat and skin thickness (d) (Iss,max = 0.0048d - 0.0052).
• Superficial shell insulation was not affected by mild leg exercise, while overall tissue insulation decreased significantly during exercise.

Conclusions:

• The superficial shell (fat + skin) demonstrates significant thermal insulation, particularly in colder conditions, and its effectiveness is directly proportional to its thickness.
• The unperfused nature of the superficial shell at rest and during mild exercise in CWT suggests limited physiological regulation of this layer.
• The poorly perfused muscle shell appears to play a more significant role in defending against body cooling at CWT than the superficial shell, especially during rest.