Increases Exercise Endurance
Green tea extract given to lab rats over a 10-week span increased the amount of time the animals could swim before becoming exhausted by as much as 24%.
Green tea's catechins appear to stimulate the use of fatty acids by liver and muscle cells. In muscle cells, the ability to burn more fat translates into a reduction in the rate at which glycogen, the form in which carbohydrates are stored for ready access in muscle, is used up, thus allowing for longer exercise times. Green tea's effect on muscle cells' ability to take in and burn fatty acids, speeding up fat breakdown, is also thought to be the reason why it helps weight loss.
The idea for the experiment came from the fact that skeletal muscles utilize carbohydrates, lipids (fats) and amino acids (protein) as energy sources, but the ratio in which they are used varies with the intensity and type of the exercise, and the level of the individual's fitness. During endurance exercise, the use of too much carbohydrate is undesirable because it triggers insulin secretion, which, in turn, both inhibits the burning of fatty acids and stimulates lactic acid production. (Lactic acid buildup is what causes that sore achy feeling in your muscles when you exercise.) Conversely, enhanced availability and utilization of free fatty acids reduces carbohydrate utilization, which in turn spares glycogen (the form in which carbohydrates are stored in muscle for quick use) and suppresses lactic acid production, resulting in an increase in endurance."
Drinking a single cup of green tea before exercise, however, will not be effective. One single, higher "dose" of green tea did nothing to improve lab rats' performance. The animals had to receive green tea daily, and endurance increased gradually over the 10 weeks of the study. To match the beneficial effect on test animals' endurance capacity seen in the experiments, the researchers estimate a 165-pound athlete would need to drink about 4 cups of green tea daily.
Research suggests that supplementing with green tea can raise your resting metabolic rate by 3%. In order to get this benefit you must have about about 3 glasses a day