Aerobic exercise influences many aspects of human health, including brain health. For example, exercise promotes the release of brain-derived neurotrophic factor, better known as BDNF, a cell-signaling protein that influences the formation, growth, survival, and development of neurons. Findings from a 2020 study suggest that exercise intensity determines which parts of the brain are affected during a workout.

Exercise intensity is defined as how hard the body works during exercise. During low-intensity aerobic exercise, a person’s heart rate is typically maintained at a steady pace of about 50 percent of its maximum ability, and workouts last for at least 30 minutes. During high-intensity aerobic exercise, a person’s heart rate is typically 75 percent of its maximum ability or higher. For example, high-intensity interval training, often referred to as HIIT, is a popular form of high-intensity exercise involving short bursts of intense aerobic exercise interspersed with periods of rest or lower-intensity exercise. During a typical HIIT session, exercisers typically achieve 80 to 100 percent of their VO2max (a measure of respiratory function) or maximum heart rate. Most HIIT workouts are brief, lasting just 15 to 30 minutes.

The study involved 25 healthy male athletes who engaged in both low-intensity and high-intensity aerobic exercise sessions on a treadmill. The sessions lasted for approximately 30 minutes and were separated by at least two days. The participants underwent a battery of tests to determine their mental state, cognitive performance, and attention. Before and after the exercise sessions, they underwent resting-state functional magnetic resonance imaging (rs-fMRI), a technique that characterizes the functional connectivity of neuronal networks when the brain is at rest.

The investigators found that the participants' moods improved after both exercise intensities. However, the rs-fMRIs revealed that the different intensities affected different parts of their brains. The low-intensity exercise turned on the activity of brain networks involved in cognitive function and attention processing. On the other hand, the high-intensity exercise turned on networks involved in mood and emotions and turned off networks involved in motor function.

These findings suggest that differing exercise intensities affect different parts of the brain during exercise and underscore the importance of varying workout programs. Learn more about the effects of aerobic exercise on health in our overview article.

• View full publication.