The effects of post-exercise sports drinks on physical performance have been extensively studied. Generally, high carbohydrate and high protein drinks following exercise accelerate recovery of liver and muscle glycogen stores and stimulate protein synthesis in skeletal muscle. Addition of other factors to the drinks, such as electrolytes, has also shown positive results in terms of metabolic changes. Because free radical generation is increased by exercise, and has been linked to tissue damage that may delay recovery, the use of post-exercise energy drinks containing antioxidants has also been researched. Green tea is a good source of flavon-3-ol antioxidant compounds, and may be beneficial in sports drinks because green tea consumption is also associated with weight loss and metabolic changes that may enhance athletic performance. This may be particularly relevant to elite athletes, because intense physical activity maybe associated with short-term detrimental changes that can impede athletic performance.
Research1 has tested the effects of a green tea and carbohydrate based electrolyte drink or mineral water in two placebo-controlled evaluations of 1 week. The subjects were Italian elite rowers from the Olympic team, and the study was both double-blinded and of a cross over design. Three blood samples were drawn from each subject at rest, after exercise and post-rehydration, and urine was collected at rest and following rehydration. All samples were analysed by 1H nuclear magnetic resonance imaging. Comparison of various metabolites in urine and blood showed that the green tea sports drink increased concentrations of citrate, 2-oxoglutarate, glucose, 3-hydroxybutyrate, lactate, acetate, acetone and caffeine, when compared to mineral water, and decreased concentrations of lactate and valine. These results suggest that a green tea and carbohydrate electrolyte sports drink can have a significant effect on certain physiological parameters.
The sports drink used to rehydrate the athletes in this study was an isotonic drink, and in agreement with previous studies, changes to metabolic parameters were reported post consumption. The effects of the green tea are unknown, because no suitable control was performed, but it is likely that consumption caused the increase in the plasma and urine caffeine concentrations. Caffeine in turn may have stimulated increases in acetone, acetate and 3-hydroxybutyrate, via increased β-oxidation leading to ketone body formation. Increased β-oxidation could account for the increased citrate levels. The increase in glucose levels would be expected with a carbohydrate based drink, and previous research has shown that carbohydrate in the form of an isotonic sports drink can increase removal of lactate. The decrease valine concentrations may be explained by increased uptake of valine to skeletal muscle and increased 2-oxoglutarate by increased oxidation of skeletal muscle.
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