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Can a cup of coffee motivate you to relish your trips to the gym this winter? That question is at the heart of a notable study of caffeine and exercise, one of several new experiments suggesting that, whatever your sport, caffeine may allow you to perform better and enjoy yourself more.

Scientists and many athletes have known for years, of course, that a cup of coffee before a workout jolts athletic performance, especially in endurance sports like distance running and cycling. Caffeine has been proven to increase the number of fatty acids circulating in the bloodstream, which enables people to run or pedal longer (since their muscles can absorb and burn that fat for fuel and save the body’s limited stores of carbohydrates until later in the workout). As a result, caffeine, which is legal under International Olympic Committee rules, is the most popular drug in sports. More than two-thirds of about 20,680 Olympic athletes studied for a recent report had caffeine in their urine, with use highest among triathletes, cyclists and rowers.

But whether and how caffeine affects other, less-aerobic activities, like weight training or playing a stop-and-go team sport like soccer or basketball, has been less clear.

So researchers at Coventry University in England recently recruited 13 fit young men and asked them to repeat a standard weight-training gym regimen on several occasions. An hour before one workout, the men consumed a sugar-free energy drink containing caffeine. An hour before another, they drank the same beverage, minus the caffeine. Then the men lifted, pressed and squatted, performing each exercise until they were exhausted.

Exhaustion arrived much later for those who’d had caffeine first. After swallowing the caffeinated beverage, the men completed significantly more repetitions of the exercises than after the placebo. They also reported feeling subjectively less tired during the entire bout and, in perhaps the most interesting finding, said that they were eager to repeat the whole workout again soon.

“Essentially, we found that with the caffeinated drink, the person felt more able to invest effort,” says Michael Duncan, a senior lecturer in sports science at the University of Exeter in England and lead author of the study. “They would put more work into the training session, and when the session was finished, in the presence of the caffeinated drink, they were more psychologically ready to go again.”

How caffeine influences the physiology and psychology of weight trainers isn’t fully understood, Dr. Duncan says. In contrast to endurance sports, an increase in fats in the blood wouldn’t provide much benefit in this kind of exercise.

Instead, Dr. Duncan says, he believes that caffeine “antagonizes adenosine,” a substance in muscles that builds up during exercise and blunts the force of contractions. The more adenosine in a muscle, the less force it generates. Caffeine reduces adenosine levels, “which then enables more forceful muscular contractions and delays fatigue,” Dr. Duncan says. “That’s the theory, anyway,” he adds.

Additional mechanisms may also be at work, other research suggests. For an experiment published last month in The Journal of Applied Physiology, researchers asked a group of volunteers who regularly play team sports to complete a grueling workout designed to simulate the physical exertion of a soccer or basketball game. Such sports commonly involve repeated bouts of intense sprinting, but little prolonged slower running. Most of the effort is anaerobic.

In the test, the volunteers performed about 16 percent better if they had ingested a caffeine capsule 70 minutes beforehand. They also, as it turned out, had far less potassium in the fluid between their muscles afterward. “We believe that potassium buildup is involved” in the kind of fatigue that occurs during anaerobic activities, like team sports and weight training, says one of the study’s authors, Magni Mohr, an exercise physiologist affiliated with both the University of Exeter and the University of Copenhagen in Denmark.

At the same time, caffeine, while affecting muscles, seems also to have a striking effect on the central nervous system and on those parts of the brain involved in mood, alertness and fine motor coordination during exercise. In a study published last month in The British Journal of Sports Medicine, soccer players dribbled, headed and kicked the ball more accurately if they’d had caffeine than if they hadn’t.

All of which would seem to indicate that a grande Americano is the ideal sports beverage. But, Dr. Mohr cautions, many questions remain. “We don’t know the best dose” of caffeine to provide performance benefits without undesirable side effects, he says, like heightened blood pressure or the jitters. In his study, volunteers consumed the equivalent of more than five large cups of brewed coffee before their workout.

Similarly, it’s not known whether people who swill cappuccinos and green tea all day get the same benefits from dosing themselves just before a workout as people who only occasionally drink caffeine, or whether the hour before a workout is the ideal moment to imbibe. Dr. Mohr suspects “it’s likely that you get more effect” if you’re not habituated to the drug, but he and others are currently studying those and similar issues and expect results soon.

In the meantime, “probably everyone can get some” fatigue-delaying and mood-enhancing benefits from caffeine, Dr. Mohr says — meaning that your gym gear should probably include a travel mug.

Correction: This article has been revised to reflect that caffeine leads to higher levels of fatty acids, not fat cells, in the bloodstream.