Mechanism involved of post-exercise cold water immersion: Blood redistribution and increase in energy expenditure during rewarming

Thermogenesis is well understood, but the relationships between cold water immersion (CWI), the post-CWI rewarming and the associated physiological changes are not. This study investigated muscle and systemic oxygenation, cardiorespiratory and hemodynamic responses, and gastrointestinal temperature during and after CWI. 21 healthy men completed randomly 2 protocols. Both protocols consisted of a 48 minutes heating cycling exercise followed by 3 recovery periods (R1-R3), but they differed in R2. R1 lasted 20 minutes in a passive semi-seated position on a physiotherapy table at ambient room temperature. Depending on the protocol, R2 lasted 15 minutes at either ambient condition (R2_AMB) or in a CWI condition at 10°C up to the iliac crest (R2_CWI). R3 lasted 40 minutes at AMB while favoring rewarming after R2_CWI. This was followed by 10 minutes of cycling. Compared to R2_AMB, R2_CWI ended at higher $\dot{{\rm V}}$ V ˙ O 2 in the non-immersed body part due to thermogenesis (7.16(2.15) vs. 4.83(1.62) ml.min −1 .kg −1 ) and lower femoral artery blood flow (475(165) vs. 704(257) ml.min −1 ) (p