The effects of rest and exercise in the cold on substrate mobilization and utilization

The effects of altering skin and core temperature by cold exposure and exercise on substrate mobilization and utilization were examined. Six subjects between the ages of 22-27 years rested and exercised in neutral and cold environments to produce 1) a neutral core and neutral skin temperature, 2) a neutral core and cold skin temperature, and 3) a cold core and cold skin temperature. Free fatty acid (FFA), glucose (GL), Lactate (LA), hemoglobin (Hb), and hematocrit (Hct) concentrations were measured along with heart rate (HR), respiratory exchange ratio (R) and oxygen consumption (VO2) after 30, 60, and 90 min of exposure to each condition. FFA, GL, LA, Hb, and Hct concentrations increased significantly during rest when both mean skin temperature (Tsk) and rectal temperature (Tre) were reduced. Plasma FFA concentration was also significantly elevated and R values were reduced during exercise when both Tsk and Tre were lowered compared to exercise in a neutral environment. No significant differences in substrate concentration, hemoconcentration, or R values were observed when Tsk alone was reduced at rest or during exercise. It is concluded that a preferential utilization of fat occurs during exercise in the cold when both Tsk and Tre are reduced compared to exercise in a neutral environment.