Bicarbonate unlocks the ergogenic action of ketone monoester intake in endurance exercise

PURPOSE: We recently reported that oral ketone ester (KE) intake before and during the initial 30 min of a ~3h 15 min simulated cycling race (RACE) transiently decreased blood pH and bicarbonate without affecting maximal performance in the final quarter of the event. We hypothesized that acid-base disturbances due to KE overrules the ergogenic potential of exogenous ketosis in endurance exercise. METHODS: Nine well-trained male cyclists participated in a similar RACE consisting of 3h submaximal intermittent cycling (IMT180') followed by a 15-min time-trial (TT15') preceding an all-out sprint at 175% of lactate threshold (SPRINT). In a randomized cross-over design participants received either i) 65g ketone ester (KE), ii) 300 mg/kg body weight NaHCO3 (BIC), iii) KE+BIC or iv) a control drink (CON), together with consistent 60g per h carbohydrate intake. RESULTS: KE ingestion transiently elevated blood D-ß-hydroxybutyrate to ~2-3 mM during the initial 2 hours of RACE (p< 0.001 vs. CON). In KE, blood pH concomitantly dropped from 7.43 to 7.36 whilst bicarbonate decreased from 25.5 to 20.5 mM (both p<0.001 vs. CON). Additional BIC resulted in 0.5 to 0.8 mM higher blood D-ß-hydroxybutyrate during the first half of IMT180' (p < 0.05 vs. KE) and increased blood bicarbonate to 31.1±1.8 mM and blood pH to 7.51±0.03 by the end of IMT180' (p