Effects of Acute Beetroot Juice Ingestion and Hypoxic Conditions on Metabolic Function, Skeletal Muscle Oxygenation,...

Exercise in hypoxic environments induces greater physiological stress than normoxic conditions, potentially limiting exercise performance through reduced skeletal muscle oxygenation and increased metabolic strain. Beetroot juice (BRJ), a dietary source of inorganic nitrate, may enhance nitric oxide (NO) bioavailability and oxygen delivery under hypoxic conditions. This study examined the acute effects of BRJ supplementation on metabolic responses, skeletal muscle oxygenation, and cardiac function during submaximal exercise at a fixed heart rate under normoxic and hypoxic conditions.

Twelve healthy adult males completed four conditions in a randomized, crossover design, with double-blinding applied to the supplementation condition: normoxic condition + placebo (NPLA), normoxic condition + BRJ (NBRJ), hypoxic condition + placebo (HPLA), and hypoxic condition + BRJ (HBRJ). Participants ingested 70 mL of BRJ (400 mg NO₃^-) or placebo 2.5 h before 30 min of submaximal exercise at 70% HRmax under normoxic (FiO₂ 20.9%) or hypoxic (FiO₂ 14.5%) conditions. A two-way repeated-measures ANOVA was used to test the main effects of environment and treatment and their interaction for each outcome.

Hypoxic conditions required a significantly lower mechanical load and induced greater physiological stress. However, a significant environment × treatment interaction was observed for Deoxy_Hb, with HBRJ statistically indistinguishable from normoxic conditions, indicating a clear attenuation of the hypoxia-induced increase in oxygen extraction. In addition, a significant main effect of treatment without a significant interaction was observed for RER, and HBRJ did not differ significantly from NBRJ.

BRJ supplementation may help attenuate hypoxia-induced skeletal muscle deoxygenation, as reflected in Deoxy_Hb, potentially via NO-mediated mechanisms; however, as circulating nitrate/nitrite concentrations were not directly measured and interaction effects were not confirmed for most variables, these findings should be regarded as preliminary evidence for the potential use of BRJ as a nutritional strategy in hypoxic exercise settings.