Acute kaempferol ingestion lowers oxygen uptake during submaximal exercise and improves high-intensity exercise capacity in well-trained male athletes.

Our previous study involving 314 highland crop species demonstrated that kaempferol, a flavonoid present in higher amounts in these species, significantly enhances mitochondrial metabolism and cellular ATP production in myoblasts under limited oxygen conditions. Notably, biologically active substances in these plants, such as phytochemicals, may help improve the health and physical strength of highland residents. Therefore, we hypothesized that kaempferol would affect oxygen availability during exercise and exercise performance in vivo. This randomized, double-blind, placebo-controlled crossover study aimed to assess the effect of a single kaempferol intake (10 mg) on cardiopulmonary response during submaximal exercises (25%, 50%, and 75% VO_2max) and maximal and super-maximal endurance capacities (100% and 125% VO_2max) in 16 well-trained male university athletes using constant-load exercise tests (VO_2max 57.5 ± 5.4 mL·kg^-1 min^-1). Kaempferol significantly reduced the VO₂ and respiratory rate during 25%, 50%, and 75% VO_2max exercises (p < 0.05 vs. placebo) without elevating the respiratory quotient and blood lactate. It also significantly increased the exercise duration at 100% VO_2max (p < 0.05 vs. placebo). Overall, we demonstrated for the first time that a single intake of kaempferol could reduce oxygen uptake (demand/cost) during constant-load submaximal exercise and extend time-to-exhaustion during maximal exercise. UMIN Clinical Trials Registry in Japan: UMIN000049589.