Additive effects of caffeine and cold water during submaximal leg exercise

Ten males exercised for 55 min at 1.5 W.kg-1 in 28 degrees C and 18 degrees C water to determine whether cold water plus caffeine (CF) ingestion had additive effects on energy production or core temperature. Two immersions were done at each water temperature, once with CF (5 mg.kg-1) and once with placebo (PL). Cold water alone (28 PL vs 18 PL) decreased free fatty acid (FFA, -13 +/- 8%) and glycerol (-37 +/- 15%) and increased lactate (18 +/- 12%), VO2 (11 +/- 3%), and minute ventilation (VE, 8 +/- 4%) but did not change glucose, heart rate (HR), respiratory exchange ratio (RER), or rectal temperature. CF alone (28 PL vs 28 CF) increased FFA (52 +/- 18%), glycerol (14 +/- 8%), lactate (28 +/- 10%), VO2 (9 +/- 3%), VE (7 +/- 5%), HR (4 +/- 1%), and rectal temperature (2 +/- 0.4%) but did not alter RER. Significant additive effects of cold water + CF (28 PL vs 18 CF) were noted for FFA, glycerol, lactate, VO2, and VE but not for RER and rectal temperature. These findings indicate that additive effects of cold water + CF alter substrate availability and increase energy production, but without a change in lipid utilization or core temperature. It may be concluded that use of CF during exercise in cold water has no physiological benefit.