Scientists evaluated the effects of caffeine during a long workout

Caffeine taken an hour before exercise increased the power of repeated sprints even 3.5 hours after ingestion. This conclusion was reached by scientists from the University of Tsukuba following an experiment involving 12 people. How noticeable the effect turned out to be and whether the results can be transferred to real competitions is described in the "Izvestia" article.

Why scientists are interested in the duration of the effect

Caffeine has long been used in sports to improve performance. However, the competition does not always end an hour after the start: in team games, intense jerks alternate with less intense stretches, and in tournaments, athletes sometimes have to enter the court several times a day. In such a situation, it is important to understand whether the effect of a single dose of caffeine persists by the end of a prolonged exercise.

The authors of the study note that many previous studies evaluated the results shortly after taking caffeine. The Japanese team decided to track how the indicators change with repeated efforts over several hours. In addition to the power of the sprints, the scientists were interested in the participants' feelings and physiological reactions: heart rate, respiration, norepinephrine concentration in the blood and blood flow parameters.

How did the experiment go?

The trial involved 12 healthy young people — eight men and four women. The average age was 24 years. Each participant underwent two trials: before one, they received caffeine at the rate of 5.5 mg per kilogram of body weight, and before the other, they received a placebo. The order was determined randomly; neither the participants nor the researchers conducting the trial knew which option was used on a particular day.

About an hour after taking the caffeine or placebo, the volunteers started exercising on an exercise bike. They performed three series at intervals of several hours. Each episode included a five-minute ride with a moderate load, followed by six extremely intense sprints lasting five seconds each. This protocol made it possible to compare the effects of caffeine at the beginning of the trial and at later stages.

The researchers measured the average and peak power of the sprints, took blood samples to determine the concentration of caffeine and norepinephrine, recorded the heart rate and respiratory parameters. Participants were also asked to rate how heavy the load seemed and how much the leg muscles hurt. Blood flow parameters related to the blood supply to the brain were evaluated separately using ultrasound methods.

What changed after taking caffeine

Compared with placebo, the average power of repeated sprints when taking caffeine was 0.5–2.4% higher. The advantage persisted throughout the trial, including 3.5 hours after ingestion. In the second and third series, peak power also increased: the difference reached 3.7%. We are talking about improving a specific indicator in a laboratory exercise, and not about the same reduction in distance time or a guaranteed advantage in a match.

Against the background of caffeine, participants rated the load as less severe and reported less pain in their leg muscles. After sprints, they were also found to have higher concentrations of norepinephrine, a substance associated with the body's response to physical exertion. According to the authors, a change in the sensations and activity of this system could accompany an improvement in the results. However, the study itself does not allow us to determine which of the observed processes played a decisive role.

Scientists have also documented other differences. After caffeine, the heart rate was higher, respiration rates changed and the blood flow rate in the middle cerebral artery decreased, which is used as one of the indirect indicators of cerebral blood supply. The university report also mentions a decrease in blood flow in the carotid artery. These data describe a physiological reaction under experimental conditions; it is impossible to draw a separate conclusion from them about the benefits or harms of changes in cerebral blood flow.

What the results can mean for sports

The authors believe that the findings can be useful in studying loads in which short intense efforts are repeated for several hours. The university cites team sports and multi-game tournaments as possible examples. The study shows that the effect of a single dose of caffeine in this model was not limited to the first segment after the warm-up.

At the same time, the test did not check the results of football players, basketball players or other athletes during real competitions. For a match, not only the power of an individual jerk is important, but also technique, decision-making, recovery, sleep, and a variety of external conditions. It would be premature to transfer the percentage difference obtained in the laboratory to the final account.

Scientists have pointed to the ability of morning coffee to disrupt sleep

The work also does not answer the question of whether the dose used is necessary for a lasting effect. For example, for a person weighing 70 kg, it would amount to 385 mg of caffeine. This is a calculation to understand the scale of the experiment, not a recommendation to repeat its scheme. The Australian Institute of Sport indicates that in some situations, smaller doses are also effective — about 2-3 mg per kilogram of body weight. The authors of the new study plan to test the effect of less caffeine separately, as well as compare a single dose with an additional or divided intake during a competition.

Why is caffeine not suitable for everyone

The results should be evaluated taking into account a small sample: only 12 young healthy people participated in the study. It does not show whether the effect will be the same for athletes of a different age, people with different caffeine habits, or with other types of exercise.

In addition, the athletic effect and dose tolerance are different issues. The European Food Safety Agency considers that for the majority of healthy adults, a single dose of up to 200 mg and a total intake of up to 400 mg per day from all sources do not cause concern based on the results of its assessment. The experimental dose for a person weighing 70 kg is approaching this daily guideline. When calculating total consumption, it is necessary to take into account not only sports supplements, but also coffee, tea, energy drinks and other caffeinated products.

Caffeine can also affect sleep and cause unwanted sensations, including palpitations and anxiety; reactions vary from person to person. Therefore, the main conclusion of the work concerns the duration of the measured effect at a specific dose and exercise: the advantage in repeated cycling sprints was maintained for at least 3.5 hours. Researchers have yet to determine the optimal amount of caffeine for longer competitions.