Caffeine and Exercise: How It Affects Your Workout

What is caffeine?

Along with alcohol and tobacco, caffeine is sometimes called a "legal drug." Unlike the other two, though, caffeine can genuinely help athletic performance, which is why it's worth a closer look.

That word "drug" is admittedly a loaded start, but since caffeine isn't a banned substance, it belongs firmly in the supplement conversation. It was actually banned in competitive sport up until around 2004, though even then the limit was fairly generous — which makes sense, since a full ban would have ruled out elite athletes having so much as a cup of coffee, cocoa, a cola, or a piece of chocolate. That would clearly be excessive.

Caffeine as a stimulant

In sport, caffeine is best known as a stimulant, which is exactly why there have been pushes to restrict it. It's long been thought to stimulate brain and heart activity, delaying the perceived signs of fatigue — a fairly established idea, though recent research suggests it may not be the whole picture. Newer studies point to a direct effect of caffeine on skeletal muscle contraction, more so than its effects on metabolism or hormones. (If that sentence didn't quite land, keep reading — here's the short version.) Caffeine helps move potassium from the fluid outside your cells into muscle cells. Once inside, potassium supports muscle contraction, which is part of why caffeine leaves you feeling more energized.

Potassium is also tied to caffeine's diuretic (fluid-flushing) effect, since potassium on its own helps push water out of the body — something competitive bodybuilders make good use of right before a show.

Caffeine also supports fat breakdown during physical activity.

In a study at Christ Church College, Canterbury, 18 runners ran 1500 m. Before the first run they were given decaf coffee, and the group's average time was 4:50. Before the second run, the same runners were given 200 mg of caffeine (about two strong cups of coffee), and their average time dropped to 4:46, with 14 of the 18 runners individually running faster.

There are a few risks worth flagging around coffee and caffeine. The first is the possibility of developing a dependence. If you stick to a moderate intake — say two or three cups a day — that's not much of a concern, but the risk becomes real at higher intakes. Overdoing caffeine mainly shows up as restlessness and a racing heart, and, with chronic overuse, long-term sleep problems. Caffeine can technically even kill you (though this is more a curiosity than a real-world risk) — the lethal dose is around 150 mg per kg of bodyweight, meaning you'd need to drink upwards of 100 cups of coffee in one sitting.

Despite these risks, which are minimal unless you're a heavy, habitual coffee or energy-drink drinker, a cup of coffee about 20 minutes before training can genuinely improve your performance in the gym — and, by extension, your results.