Exogenous Ketosis during Early Acclimatization at High Altitude: Ventilatory, Cardiovascular and Muscular Responses to Maximal Exercise.

Background: Exogenous ketosis, induced via ketone monoester (KE) ingestion, can attenuate blood desaturation and muscle deoxygenation during hypoxic exercise. However, its effect(s) on exercise capacity and underlying integrated physiological responses to incremental exercise to exhaustion during early acclimatization at terrestrial high altitude remain unexplored.

Methods: Healthy active adults were randomised to an intermittent exogenous ketosis (IEK; n = 16) or placebo (PLA, n = 17) group, before performing two incremental cycling tests to volitional exhaustion. The first was conducted at sea level (295 m) without prior supplementation. The second was conducted at high altitude (3375 m) following ~69 hours of acclimatization, during which participants intermittently ingested KE (IEK) or placebo (PLA). During exercise, gas exchange, cardiac output, and both blood and muscle oxygenation were recorded continuously using a metabolic cart, transthoracic impedance, earlobe oximetry and near-infrared spectroscopy, respectively.

Results: Pre-exercise blood ketone concentrations were higher in IEK than PLA (~2.1 mM vs. ~0.3 mM, P < 0.001). However, both experimental groups exhibited comparable (P = 0.525-0.644) high altitude-induced reductions in peak power output (P < 0.001), as well as in blood (P < 0.001) and muscle oxygenation (P < 0.001) during maximal exercise and submaximal power levels. Furthermore, high altitude significantly increased resting and/or exercising ventilation (P < 0.001) and cardiac output (P < 0.001), yet irrespective of the KE vs. placebo ingestion (P = 0.529-0.828).

Conclusions: These findings indicate that intermittent exogenous ketosis during early acclimatization does not mitigate altitude- and exercise-induced reductions in blood and muscle oxygenation. Moreover, it does not importantly modulate ventilatory and cardiac output responses, and therefore does not seem to confer ergogenic advantage during subacute high altitude exposures.