Muscle temperature increases during a single far infrared sauna session without changes in intestinal temperature.

Area of Science:

• Therapeutic modalities
• Exercise physiology
• Biomedical engineering

Background:

• Increases in muscle temperature during exercise and passive heating are linked to beneficial health outcomes.
• Far infrared (FIR) saunas are a popular radiant heating method, with claims of deep tissue penetration.
• The actual muscle temperature response to FIR sauna bathing remains unquantified.

Purpose of the Study:

• To quantitatively assess muscle temperature changes at varying depths during a FIR sauna session.
• To investigate the depth of heat penetration into peripheral tissues from FIR sauna use.

Main Methods:

• Ten adult participants underwent a 45-minute FIR sauna session.
• A multi-sensor intramuscular temperature probe measured muscle temperature at superficial (1.4 cm), middle (2.4 cm), and deep (3.4 cm) locations within the quadriceps.
• Muscle, core, and skin temperatures, along with body weight, were recorded before and after the session.

Main Results:

• Muscle temperature significantly increased at all measured depths: superficial (+3.0°C), middle (+1.9°C), and deep (+1.1°C).
• Core body temperature showed no significant change, while mean skin and body temperatures increased significantly.
• The magnitude of muscle temperature increase was inversely related to depth, indicating superficial heating.

Conclusions:

• Far infrared saunas primarily induce superficial heating of peripheral tissues.
• The claimed deep penetration of FIR waves into muscle tissue was not supported by these findings.
• These results suggest FIR saunas may not provide the deep heating benefits sometimes attributed to them.