“If we put you on a treadmill and told you to go as long as you can, you’ll run farther if you’ve had caffeine than if you haven’t,” says Matthew Ganio, who heads the department of health, human performance, and recreation at the University of Arkansas.

(Researchers typically give people between 1.4 and 2.7 milligrams of caffeine per pound of body weight an hour before exercise. For a 150-pound person, that means roughly 200 to 400 mg of caffeine. And more isn’t better. Higher doses don’t give more of a boost and can cause side effects.)

How much of a boost?

On average, people who have had caffeine run about 12 percent farther when they push themselves to exhaustion. “But there’s almost never a setting where you’re pushing yourself until you can’t go anymore,” Ganio points out.

So he looked at the research that gauged whether caffeine could slash the time it takes to, say, run a 5-kilometer race or row 2,000 meters. After analyzing the results from 21 studies (which enrolled mostly young, fit men), he calculated that caffeine could boost performance by about 3 percent.

“That may not seem like a lot to the recreational athlete,” says Ganio, “but it would be quite the difference in the Olympics.”

Not an Olympian?

“The average person can still reap the benefits,” says Ganio.

In one study, researchers enrolled 12 Australian men who typically exercised less than an hour a week. On two separate days, the men took a placebo or 2.7 mg of caffeine per pound of body weight an hour before riding stationary bikes for 30 minutes. On the day they got caffeine, the men burned 5 percent more calories, pedaled 5 percent harder, and pushed their heart rate 5 percent higher, all without feeling like they were working harder.

Few studies have looked at the exercise-boosting effects of caffeine in older adults, Ganio points out.

“But I can’t think of a reason why it wouldn’t help them.”

In one study, 19 British adults aged 61 to 79 performed a battery of physical tests an hour after taking a placebo or 1.4 mg of caffeine per pound of body weight. On the day they got the caffeine, the volunteers were able to do one more bicep curl in a 30-second test and walk about 100 feet farther in a 6-minute test than when they took the placebo.

How caffeine helps

Why might the caffeine in two-or-so cups of coffee give your workout a jolt?

For one, “it reduces feelings of fatigue,” says Ganio. Caffeine can also blunt the perception of muscle pain. “And, at a given pace, people will rate exercise as less difficult when they’ve had caffeine.”

Taken together, that means that caffeine may make exercise feel a bit easier.

“In turn, maybe you’re able to push yourself a little harder,” says Ganio.

A word of caution

Caffeine is safe for most adults if they don’t overdo it. But it has some downsides:

  • Too much caffeine can make you jittery and disturb your sleep.
  • Caffeine doesn’t cause hypertension, but it can raise your blood pressure for several hours.
  • Energy drinks have been linked to irregular heart rhythms and increases in heart rate and blood pressure. Don’t get carried away.

Photo: Mariia-Korneeva/stock.adobe.com.