Effects of elevated plasma adrenaline levels on substrate metabolism, effort perception and muscle activation during low-to-moderate intensity exercise

Abstract

The aim of this study was to differentiate the role of raised plasma adrenaline (Adr) concentrations from sympathoadrenal activation associated with moderate-intensity exercise, on muscle activation, cardiopulmonary responses, fuel metabolism, and ratings of perceived exertion (RPE) during low-intensity exercise. Two groups of subjects (MOD, n = 6; LOW, n = 7) cycled on two occasions for 90 min. MOD cycled at 68% VO2max with saline infusion, and at 34% VO2max with Adr infusion. LOW cycled twice at 34% VO 2max, with either Adr or saline infusion. Infusions (0.015 g Adr/kg/ min) started at 15 min and increased plasma [Adr] somewhat higher than during exercise at 68% VO2max (∼1.9 vs. 1.4 nM, at 75 min). Mean plasma glucose and lactate concentrations during LOW were significantly higher with Adr than saline infusion (5.1 ± 0.6 vs.4.4 ± 0.3 mmol/l, P < 0.01 and 2.1 ± 0.8 vs. 1.3 ± 0.5 mmol/l, P < 0.01, respectively). Elevated [Adr], without increased exercise intensity, did not alter glycogenolysis. There were also no effects of Adr infusion at 34% VO 2max on heart rate, oxygen consumption, [FFA], respiratory exchange ratio, intramuscular triglyceride utilization, muscle activation or RPE. In conclusion, elevated [Adr] similar to those found during moderate-intensity exercise increased plasma glucose and lactate availability, but did not alter intramuscular fuel utilization, effort perception or muscle activation.