Dose–Response Effects of p‐Synephrine on Fat Oxidation Rate During Exercise of Increasing Intensity

Jorge Gutiérrez‐Hellín, Juan Del Coso

The aim of this investigation was to determine the effects different doses of p-synephrine on maximal fat oxidation during exercise. Seventeen healthy subjects volunteered to participate in a double-blind and randomised experimental design composed of four identical experimental trials. On four trials separated by 72 h, participants ingested a placebo or 1, 2 or 3 mg/kg of p-synephrine. After resting for 60 min to allow substance absorption, participants performed an exercise test of increasing intensity on a cycle ergometer while gas exchange was measured continuously. None of the doses of p-synephrine affected energy expenditure or heart rates during the test. The highest rate of fat oxidation with the placebo (0.35 ± 0.05 g/min) was reached at 38.0 ± 1.9% of VO2max . The ingestion of 1 mg/kg increased maximal fat oxidation to 0.47 ± 0.11 g/min (p = 0.01) but did not change the intensity at which it was obtained (42.0 ± 9.4% of VO2max ). The ingestion of 2 and 3 mg/kg of p-synephrine increased maximal fat oxidation to 0.55 ± 0.14 g/min (p < 0.01), although only 3 mg/kg slightly changed the intensity at which it was obtained (43.0 ± 9.5% of VO2max , p < 0.01). In conclusion, although all p-synephrine increased the maximal rate of fat oxidation during exercise, the highest effects were found with 2 and 3 mg/kg. Copyright © 2017 John Wiley & Sons, Ltd.