(-)-Epicatechin Supplementation Inhibits Aerobic Adaptations to Cycling Exercise in Humans.

The purpose of the study was to determine if cycling exercise combined with (-)-epicatechin supplementation was more effective at increasing training adaptations than cycling combined with a placebo. Blood and muscle samples were obtained at rest before and after training to determine the effects of (-)-epicatechin supplementation on total serum antioxidant capacity, skeletal muscle mitochondrial protein content, and skeletal muscle myostatin gene expression. Participants (n = 20) completed two testing sessions separated by 4 weeks of cycle training, with supplementation of 100 mg (200 mg total daily) of (-)-epicatechin or a placebo, twice daily. Data were analyzed using a two-way mixed model ANOVA for each variable and the alpha level was set at p ≤ 0.05. A significant increase was observed for time for relative peak anaerobic power (p < 0.01), relative anaerobic capacity (p < 0.01), and fatigue index (p < 0.01). A significant increase was observed for time for absolute peak VO₂ (p < 0.01) and peak power output obtained during the peak VO₂ test (p < 0.01). A significant interaction between group and time for relative peak VO₂ was observed (p = 0.04). Relative peak VO₂ significantly increased over time in the placebo group (p < 0.01), but not in the (-)-epicatechin group (p = 0.21). A significant increase was observed for time for total serum antioxidant capacity (p = 0.01). No interaction or main effect of time was observed for myostatin (p > 0.05). Likewise, no interaction or main effect of time was observed for cytochrome C or citrate synthase (p > 0.05). A significant interaction effect was observed for succinate dehydrogenase (SDH; p = 0.02). SDH content increased significantly for the placebo group (p = 0.03, partial η² = 0.59), but not for the (-)-epicatechin group (p = 0.81). Further, whereas no difference existed between the groups for SDH at baseline (p = 0.23), SDH content was significantly greater in the placebo group at the post time point (p = 0.01). Results indicate that (-)-epicatechin supplementation does not affect myostatin gene expression or anaerobic training adaptations but inhibits aerobic and mitochondrial SDH adaptations to cycle exercise training.