A single dose of purple grape juice improves physical performance and antioxidant activity in runners: a randomized, crossover, double-blind, placebo study

PURPOSE: To investigate the effects of a single dose of juice on physical performance, oxidative stress, inflammation and muscle damage in runners. METHODS: Fourteen recreational male runners (39 ± 9 years, VO(2peak) = 55.9 ± 6.5 ml/kg/min) performed two running tests to exhaustion at 80% of VO(2max) after ingesting grape juice or a placebo drink (10 ml/kg/day) randomly. Blood samples were taken before and 2 h after supplementation and immediately after running to analyze total antioxidant capacity (TAC), malondialdehyde (MDA), alpha-1 acid glycoprotein (A1GPA), high-sensitivity C-reactive protein (hs-CRP), creatine kinase (CK) and lactate dehydrogenase (LDH). RESULTS: The participants ran for an average of 59.2 ± 27.8 min until exhaustion in the placebo group and for 68.4 ± 29.7 min until exhaustion in the grape juice intake group, which was a significantly longer time (p = 0.008). This improvement in physical performance was accompanied by a 43.6% increase in TAC (p = 0.000) at the post-exercise timepoint compared to the level at baseline. MDA, A1GPA, hs-CRP, CK, and LDH did not exhibit changes. In contrast, no significant change in any variable was observed after consuming the placebo drink. CONCLUSION: The single-dose intake of purple grape juice demonstrated an ergogenic effect in recreational runners by increasing run time to exhaustion and increasing antioxidant activity.