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Why? Caffeine improves endurance, most likely through its effect on the brain, changing your perceptions of exertion and pain.
When? An hour before exercise. “Caffeine takes 50 to 90 minutes to reach peak levels in your blood,” says Dr Matthew Ganio of the University of Connecticut.
How much? Roughly 2.8 to 5.4mg per kilo of body weight.
Pick one that has carbs and electrolytes, such as USN Active Sports Drink (Fruits of the Forest flavour) with 108mg caffeine. An energy drink like Red Bull (76mg caffeine) contains ingredients that have unknown effects on your performance, says Ganio.
This is popular with some elite athletes, but its sweetness and kilojoules may upset your stomach. A 330ml can of coke contains 33mg caffeine.
A typical 250ml mug of instant coffee has 60mg caffeine. It may not be the wisest choice, though – not because it’s a diuretic (that’s a misconception, says Ganio), but because compounds in coffee beans known as chlorogenic acids may reduce the caffeine’s potency.