Kaempferol enhances oxygen utilization efficiency during maximal incremental and constant-load exercises in healthy men: a randomized trial

Hypoxia can occur in daily life, and exercise is a potential trigger. Intense exercise increases oxygen demand in muscles, potentially compromising performance by reducing ATP resynthesis. Kaempferol (KMP) increases intracellular ATP resynthesis in hypoxic cellular models. We investigated the effects of KMP on oxygen utilization during exercise in a general human population. Study 1 (Ramp-incremental cycling test): Overall, 20 men were randomized to four groups and administrated placebo, 2.5, 10, or 25 mg KMP for 8 days in a crossover design. Measurements of oxygen utilization efficiency slope (OUES), maximal oxygen uptake (VO2max), peak heart rate (HR), VO2 and work rate at gas-exchange threshold, minute ventilation/carbon dioxide output ratio (VE/VCO2) slope, and post-exercise muscle tightness and breathing difficulty were performed on days 1 and 8. Study 2 (Constant-load cycling test): Overall, 25 men were randomized to groups that received either a single dose of 10 mg KMP or a placebo in a crossover design. VO2/VE, VO2max, VO2, respiratory rate, HR, respiratory exchange ratio, and VE/VCO2 were measured at exercise intensities of 25%, 50%, and 75% of VO2max. Study 1: Both OUES and VO2max showed significant dose-dependent increase on day 1. The optimal dose and frequency for the ergogenic effects of KMP was found to be 10 mg in a single intake. Study 2: KMP improved VO2/VE and enhanced respiratory and cardiovascular indices. KMP enhances the maximum capacity for oxygen utilization and improves oxygen utilization efficiency at several exercise levels. Study 1: UMIN000049587 (November 23, 2022); Study 2: UMIN000049590 (November 23, 2022) (UMIN Clinical Trials Registry).