Twice the caffeine, the same jump: boxers given 6 mg per kilo leapt no higher than on half that dose. Only one of ten strength tests clearly favoured the bigger dose, which for these men meant more than 400 mg in one go

Caffeine is one of the few supplements with solid evidence that it helps athletes, and the usual advice is a dose somewhere between 3 and 6 milligrams per kilogram of body weight, about an hour before the effort. That is a wide range. For a 74 kg man, the average weight in this study, it runs from about 220 mg to about 440 mg. A trial published in the Journal of the International Society of Sports Nutrition on 7 October 2026 asked whether the top of the range buys anything the bottom does not.

The volunteers were 15 male boxers from Beijing Sport University, average age 21, with about four years of training and a national second-class athlete ranking or better. Each came to the lab three times, a week apart, and swallowed capsules that looked the same every time: maltodextrin alone, 3 mg/kg of caffeine, or 6 mg/kg. Neither the boxers, the testers nor the people analysing the data knew which was which. The order was shuffled so that each dose came first, second and third equally often. For 48 hours before every visit the men were asked to have no coffee, tea or energy drinks.

Each visit followed the same script: a warm-up, a set of tests, the capsules, then the same tests again in blocks starting 30 and 60 minutes later. The tests were a standing jump on a force plate, an explosive push-up in which the hands leave the floor, and a machine that measures the maximum turning force of the shoulder and the knee. Ten measurements in all.

The jump gave the cleanest answer. In the 60-minute block, jump height was 45.0 cm after the dummy capsule, 48.9 cm after the moderate dose and 50.1 cm after the double dose. Both doses beat the dummy clearly, by about 4 and 5 cm, but the 1.2 cm between the two doses was not a real difference by the study's own statistics. Jump power followed the same pattern. On this test, doubling the dose bought nothing that 15 people could detect.

The explosive push-up moved only on the double dose, and only in the 60-minute block. The authors are frank that this result is fragile: the push-up scores wobbled a lot from one attempt to the next, and the gains on the double dose were only about one to one and a third times the test's ordinary measurement error.

The leg machine is where the double dose stood out. Knee extension, the thigh muscles straightening the leg, reached 223 newton-metres in the 60-minute block on the double dose, against 197 on the moderate dose and 182 on the dummy. That was the only one of the ten measurements where 6 mg/kg beat 3 mg/kg by a margin the statistics accepted. Shoulder strength rose on both doses, with no clear edge for the higher one.

Two details in the tables are worth knowing before reading too much into the jump gains. On the dummy days, the boxers got slightly worse as the session went on: their jump fell from 47.1 cm before the capsule to 45.0 cm an hour later, so part of caffeine's lead is the dummy group tiring or cooling off. And on the two caffeine days they started lower, 43.2 and 44.0 cm, before they had swallowed anything. The authors say they did not treat these starting differences as an effect of the capsules, which is right, but they mean the comparison at 60 minutes is less tidy than the headline numbers suggest.

The authors list the other limits themselves. Fifteen people is too few to call the two doses equal on the tests where they did not differ. The trial was not registered in advance and no single main outcome was named before it began. Nobody measured caffeine in the men's blood, asked how much coffee they normally drank, or recorded side effects with a proper questionnaire, and the 48-hour break from caffeine may have left regular drinkers in mild withdrawal on the dummy days. Most of all, none of the tests was a punch. The authors stress that a jump, a push-up and a knee machine measure qualities that matter in boxing, not boxing itself.

Where does that leave someone weighing up a pre-training coffee? This is one small study in young male athletes, and it fits earlier work: the moderate dose did most of what caffeine does here, and the double dose added a clear gain on one leg test of ten. The cost side matters too. The European Food Safety Authority says single doses up to about 200 mg, roughly 3 mg/kg, raise no safety concern for healthy adults, including before hard exercise, and that up to 400 mg spread over a day is fine for healthy adults other than pregnant women. A 6 mg/kg dose for a 74 kg man is about 444 mg in one go, more than that whole daily figure.