Exogenous ketosis does not alter oxygenation, oxygen uptake kinetics, or whole-body efficiency during submaximal exercise in early high-altitude acclimatization

Thirty-four healthy, active adults completed four exercise sessions, one near sea level and then one per day over a 3-day stay at 3,375 m, with regular ketone monoester or placebo ingestion. Ketone monoester induced ketosis at the start of each session, but compared with placebo it produced a comparable high-altitude slowing of the primary phase time constant of VO2 kinetics during heavy-intensity exercise (group by time interaction P = 0.501). Gas exchange, ventilation, pulse oxygen saturation and brain tissue saturation changes were similar between groups, and whole-body energy efficiency was preserved in both groups. Ketone monoester increased cardiac output during moderate-intensity exercise on the first altitude day (P = 0.042).