Increased cardiorespiratory stress during submaximal cycling after ketone monoester ingestion in endurance-trained adults

In a randomized, double-blind, counterbalanced study, 19 endurance-trained adults (10 males, 9 females) ingested a ketone monoester (600 mg/kg body mass) or placebo before a 30-minute cycling bout at ventilatory threshold intensity followed by a 3 kJ/kg time-trial. Ketone monoester raised pre-exercise plasma beta-hydroxybutyrate (3.9 versus 0.2 mM), ventilation (77 versus 71 L/min), heart rate (155 versus 150 beats/min) and end-of-exercise rating of perceived exertion (15.4 versus 14.5). Time-trial performance did not differ (16:25 versus 16:06 min:s, p = 0.20).