Waseda University reveals that light-intensity exercise for only 10-20 seconds increases cerebral blood flow in children

A research group led by Takashi Naito, a doctoral student at the Graduate School of Sport Sciences, and Professors Kaori Ishii and Koichiro Oka of the Faculty of Sport Sciences at Waseda University measured changes in cerebral blood flow in the frontal region of the brain during seven types of light-intensity exercise using a dedicated device called functional near-infrared spectroscopy (fNIRS). The study involved 41 children ranging from the fifth grade of elementary school to the third grade of junior high school with a mean age of 12.1 years. The researchers found that monotonous stretching movements, such as folding both hands and extending them upward, did not significantly increase cerebral blood flow, but light-intensity exercises with certain physical and cognitive loads, such as trunk twisting in a chair, finger movement exercises, and standing on one leg, resulted in a marked increase in cerebral blood flow. The research group hopes that "the findings may be used to develop short-duration, low-intensity exercise programs that are easy for everyone and improve children's cognitive function." The results were published on July 6 in Scientific Reports, an online general scientific journal of the Nature Publishing Group.

Many studies have shown the positive effect of exercise on executive function, a higher cognitive function, and factors thought to contribute to this effect include increased cerebral blood flow, structural changes in the brain, and increased neural efficiency. Among these factors, previous studies have shown that cerebral blood flow increases during and immediately after moderate- to high-intensity aerobic exercise. However, virtually no studies have examined changes in cerebral blood flow during low-intensity exercise, and no previous studies have focused specifically on children.

Previous studies have also been conducted with a single type of exercise, such as cycling or running alone, and no studies have examined the effects of different types of exercise on cerebral blood flow. Moreover, guidelines of WHO and different countries recommend that children engage in moderate- to high-intensity physical activity for at least 60 minutes per day. However, more than 80% of children worldwide do not meet this recommended level. Furthermore, recent reports have shown that increased low-intensity physical activities, such as standing while talking, stretching, and slow walking, are beneficial for improving obesity indices and cardiovascular health in children. Increasing attention is being drawn to the benefits of low-intensity physical activities and exercises that are easier to engage in.

Considering the ease of performance at educational settings, such as schools and homes, the Waseda University research group focused on low-intensity exercise as it can be performed at any site without any special equipment. They investigated the effects of these exercises on blood flow in the prefrontal cortex of the brain, which is responsible for executive function. Seven types of exercise were used in the experiment: upward stretch, shoulder stretch, elbow circles, trunk twist, washing hands, thumb and pinky (one hand extends the thumb, the other hand extends the little finger, and these are repeated alternately with the left and right hands), and single leg balance. Because head tilt and movement affect fNIRS readings, exercises involving as little head movement as possible were chosen. The exercises did not include forward or backward bending of the trunk.

The children performed seven low-intensity exercises in two patterns of 10 and 20 seconds per movement. Each pattern consisted of two bouts of each exercise with a 10-second rest per event and a 30-second rest before moving to the next event. The oxygenated hemoglobin level, an index of cerebral blood flow, was then measured at rest (0-5 seconds before the start of exercise) and during exercise for each type of exercise using fNIRS attached to the frontal region of the subjects' head. In the post-measurement data analysis, the prefrontal cortex was divided into left, middle, and right regions, and changes in cerebral blood flow in each region were calculated.

The results showed that the monotonous stretching movements, such as upward and shoulder stretches, were not associated with major changes between oxygenated hemoglobin levels at rest and during exercise. However, cerebral blood flow measurements in at least one region increased significantly during elbow circles, trunk twists, washing hands, thumb and pinky, and single leg balance with increased physical and cognitive loads compared to that at rest. A per-movement comparison between the 10- and 20-second movement patterns showed no significant difference.

These results indicate that low-intensity exercises activate the prefrontal cortex and increase cerebral blood flow even in short durations, provided they entail certain cognitive and physical loads. However, they noted that further investigation is necessary to verify whether the observed effects actually lead to improved executive function.

Journal Information
Publication: Scientific Reports
Title: Hemodynamics of short-duration light-intensity physical exercise in the prefrontal cortex of children: a functional near-infrared spectroscopy study
DOI: 10.1038/s41598-024-66598-6