# Nineteen elite swimmers received 10 sessions of dual-site brain stimulation across 25 days and finished with faster reactions stronger mental toughness and better 100-meter performances > Ten sessions of mild electrical brain stimulation helped a small group of elite male swimmers improve their 100-meter freestyle times. The swimmers also responded faster during reaction tests and reported feeling fatigue later in the race. The findings come from a study... Canonical URL: https://www.argo.net/nineteen-elite-swimmers-received-10-sessions-of-dual-site-brain-stimulation-across-25-days-and-finished-with-faster-reactions-stronger-mental-toughness-and-better-100-meter-performances/ Byline: ARGO.net Editorial Team Published: 2026-08-19T03:30:03+00:00 Updated: 2026-08-19T10:29:28+00:00 Categories: Explainer, Health ![Competitive swimmer wearing goggles after training](https://www.argo.net/wp-content/uploads/2026/08/competitive_swimmer_training_licensed.jpg) Ten sessions of mild electrical brain stimulation helped a small group of elite male swimmers improve their 100-meter freestyle times. The swimmers also responded faster during reaction tests and reported feeling fatigue later in the race. The findings come from a [study published](https://www.nature.com/articles/s41598-025-27803-2) in **Scientific Reports** on December 17, 2025. Researchers followed 19 swimmers during a 25-day experiment that compared real stimulation with a sham treatment designed to feel similar. The results offer an early look at how repeated **[transcranial direct current stimulation](https://www.nimh.nih.gov/health/topics/brain-stimulation-therapies/brain-stimulation-therapies)**, known as tDCS, might support athletic training. The trial was small, involved only young male swimmers and used handheld stopwatches, so larger studies will be needed before coaches can judge whether the method provides a reliable competitive advantage. ## How weak electrical currents stimulate the brain Transcranial direct current stimulation sends a steady, low electrical current through electrodes placed on the scalp. In this experiment, the current was set at **2 milliamps**, a small amount and each treatment lasted 20 minutes. The current aims to alter how easily groups of brain cells respond to signals. Brain cells communicate through electrical and chemical activity and a mild current can make some cells slightly more ready to fire. The effect depends on electrode placement, current direction, treatment length and what a person does during or around the session. Researchers placed two positive electrodes over the left side of the swimmers' heads. Two larger negative electrodes were positioned near the right forehead. Saline-soaked sponges helped carry the current between the equipment and the scalp. tDCS has been explored in medicine, learning research and sports science. Results across athletic studies have varied, partly because researchers have stimulated different brain areas and used different exercise tests. The number and timing of sessions also differ widely. ## Nineteen elite swimmers joined the trial Nineteen male swimmers with an average age of 19 completed the study. They had trained for an average of more than 11 years and usually completed about eight or nine training sessions each week. According to the paper, each athlete ranked among the top three swimmers in his country within his discipline. The researchers ranked the athletes using recent performance records and divided them into two groups with similar records. Ten received active stimulation, while nine completed the sham program. The athletes were unaware of which treatment they received, although the staff member operating the stimulation equipment knew each assignment. The **randomized sham-controlled trial** took place over 25 days near the swimmers' regular training pool. The testing schedule was built around their normal preparation period, allowing the athletes to continue eight pool sessions and two gym sessions per week. Before treatment, the researchers measured swimming performance in the morning and evening. They also tested reaction speed, mental toughness, estimated arm strength, blood lactate, heart rate and the distance at which each swimmer first felt fatigue. ## Why researchers targeted two brain regions One electrode targeted the primary motor cortex, called **M1**. The motor cortex helps the brain plan and control voluntary movement. During swimming, it contributes to the stream of signals that travels from the brain through the spinal cord and into working muscles. The second electrode targeted the left dorsolateral prefrontal cortex, called the **DLPFC**. The region supports attention, decision-making and control over thoughts and actions. Researchers have also linked it to effort, fatigue and the ability to continue a difficult task. Swimming combines precise movement with intense physical effort. A sprinter must launch quickly, keep an efficient stroke, manage rising discomfort and respond to feedback from muscles and breathing. Stimulating two areas at once was intended to reach both movement control and the mental processes involved in sustained effort. Earlier experiments had suggested that dual-site stimulation could produce stronger or longer-lasting changes in brain activity than stimulation at one location. The swimmer trial tested whether repeated sessions could build on those changes while athletes continued their usual training. ## One session produced little change A single active session was delivered between morning and evening swimming tests. The schedule allowed researchers to examine whether one 20-minute treatment helped athletes recover or perform better later that day. The acute treatment produced no significant group difference in 100-meter performance from morning to evening. Researchers also found no meaningful difference in heart rate, blood lactate, or the reported distance where fatigue began. Single-session sports studies have produced mixed results. Some have reported changes in endurance or perceived effort, while others found little effect on performance. Small differences in electrode position, exercise type, athlete experience and testing time could help explain the uneven findings. The elite level of the participants may also have limited immediate gains. Highly trained swimmers have already developed efficient movement patterns and strong physical conditioning. Detecting a small added benefit can be difficult when performance is already near an athlete's current limit. ## Ten sessions improved 100-meter swim times The longer program delivered active or sham stimulation three days per week between morning and evening training. Forty-eight hours after the tenth session, the swimmers repeated their morning and evening tests without receiving stimulation between the two swims. After researchers adjusted for the athletes' starting scores, the active group showed greater improvement in both morning and evening **100-meter freestyle** performance than the sham group. The statistical result narrowly reached the usual significance threshold in the morning test and was stronger in the evening test. The experiment could not establish exactly how the stimulation influenced swimming speed. One possibility involves changes in the brain networks that send movement commands to the muscles. Repeated treatment alongside training might also support learning and coordination, although the study did not directly measure brain activity or swimming technique. Evening blood lactate was higher in the active group after the ten-session program. Lactate rises during intense exercise as muscles rapidly process fuel. The increase may indicate that swimmers reached a higher level of effort, although lactate alone cannot explain why their times improved. ## Swimmers felt fatigue later in the race Researchers introduced a measure called **distance of perceived fatigue**. After each 100-meter swim, athletes reported the point in the race where they first felt fatigued and began concentrating mainly on reaching the finish. Swimmers in the active group reported that fatigue began more than 10 meters later after the repeated treatment. The average shifted from about 60 meters to roughly 72 meters, while the sham group reported a change of about three meters. The measurement offers a race-specific view of fatigue. A general effort scale can be less useful after an all-out sprint because nearly every swimmer finishes in a state of severe exertion. Asking where fatigue began may capture changes that occur before the finish. The measure remains experimental. It relies on memory and personal judgment and it has not been fully tested for reliability. Coaches involved in the study considered it relevant because experienced swimmers can often identify where their stroke begins to weaken, but future work must compare the reports with direct measurements of technique and speed across the pool. ## Reaction times and mental toughness improved All three forms of **reaction time** improved more in the active group than in the sham group. The athletes completed two sound-based tests and one visual test. Researchers recorded each swimmer's best response and the average across several attempts. Fast reactions can influence a sprint race from the opening signal. A quicker start may save a small amount of time before the swimmer enters the water. Reaction testing can also provide clues about attention and how quickly the brain converts a signal into movement. Total **mental toughness** scores also improved significantly in the active group. The questionnaire measured confidence, constancy and control, although changes within those individual parts did not reach statistical significance. The overall result should therefore be treated as preliminary. The study did not determine whether faster reactions directly caused better swim times. Repeated testing may improve familiarity and the stimulation could have influenced several processes at once. The combination of training and repeated stimulation may be important, since the treatment sessions took place during the swimmers' regular preparation program. ## Heart rate and upper-body strength stayed similar Heart rate after the swimming tests remained similar between the active and sham groups. The study abstract stated, "No significant differences were found for HR and 1-RM scores." The **heart rate** result suggests that improved times did not come with a clear change in the athletes' immediate cardiac response. Heart rate was measured after each race, so the experiment did not track every rise and fall during the swim itself. Upper-body strength was estimated with a one-arm preacher curl. Athletes lifted a dumbbell weighing between 10 and 20 kilograms for fewer than nine repetitions and the researchers used a standard formula to estimate the maximum weight each person could lift once. The strength estimate rose more in the active group, but the difference fell short of statistical significance. A larger study might clarify whether the apparent change was meaningful or reflected normal variation. The test also focused on the biceps, while sprint swimming depends on coordinated force from much of the body. ## Small sample leaves important questions The **small sample size** is the clearest limit. A trial with 19 participants can detect large differences, yet smaller effects may appear unstable or disappear when tested in a broader population. The results also apply directly only to elite young male swimmers under the conditions used in this experiment. Timing was measured by two experienced coaches using handheld digital stopwatches. Automatic touchpads would provide greater precision, especially when expected improvements may involve fractions of a second. The researchers also did not monitor sleep quality, which can affect reaction speed, physical performance and perceived fatigue. Blinding presents another concern. The swimmers did not know their assignments, but the person administering the treatment did. The study did not formally test whether participants could correctly guess which condition they received. Sensations such as tingling can sometimes reveal active stimulation, even when a sham treatment includes a brief current at the beginning and end. The study's [medical record](https://pubmed.ncbi.nlm.nih.gov/41408102/) identifies it as a randomized controlled trial, while the full paper available through [PubMed Central](https://pmc.ncbi.nlm.nih.gov/articles/PMC12714799/) provides the detailed methods and limitations. Independent trials with more swimmers, automatic timing, stronger blinding and direct measurements of brain activity could test whether the performance effects hold up. Questions about fairness and [sports regulation](https://www.wada-ama.org/en/prohibited-list) may also grow if brain stimulation produces repeatable gains. The present experiment supplies early evidence from a narrow group and it does not establish a standard training method. Safety monitoring, long-term follow-up and clear sporting rules would be needed before repeated tDCS became common around elite competition.