Exogenous ketosis impacts neither performance nor muscle glycogen breakdown in prolonged endurance exercise

In a randomized crossover design, 12 highly trained male cyclists completed a simulated race of 3 hours of intermittent cycling, a 15-minute time trial and a maximal sprint, receiving 60 g carbohydrate per hour plus three boluses (25, 20 and 20 g) of ketone ester or a control drink. Ketone ester raised blood d-beta-hydroxybutyrate to about 3 mM, lowered blood pH from about 7.42 to 7.36 and dropped bicarbonate from 26.0 to 21.6 mM. Net muscle glycogen breakdown was similar between conditions, as were mean time-trial power (273 versus 272 W, P = 0.83) and sprint time to exhaustion (59 versus 58 s, P = 0.66).