Active Voice: Lighting Up the Brain During Exercise
By Gavin D. Tempest, Ph.D.
NIRS devices use light to measure changes in blood flow (i.e., oxygenation). Initially, in exercise science, NIRS was used to measure oxygenation in muscle tissue. However, its application to monitor changes in oxygenation in the brain, like during cycling exercise, has become increasingly popular. When placed on the scalp, changes in oxygenation, in turn, reflect local brain activity. NIRS is lightweight and portable, which adds to its suitability for measuring the brain during cycling exercise.
When applying NIRS to measure brain activity during cycling exercise, one of the potential challenges is that systemic changes associated with the increased physiological load (e.g., increased blood pressure, heart rate and respiration) also account for changes in cerebral blood flow. What we do not know is if NIRS devices can measure changes in brain activity related to brain function (e.g., cognition) distinct from the systemic effects induced during exercise.
In our study, as presented in the May 2019 edition of Medicine & Science in Sports & Exercise® (MSSE), we investigated the utility of using NIRS to measure task-evoked brain activity during cycling exercise at different intensities. We examined multiple periods of cycling as well as cycling plus a cognitive (working memory) and motor (hand grip) task at rest during low-, moderate- and high-intensity exercise. Our findings indicated that brain activity linked to the tasks could be identified during low and moderate exercise. Brain activity also linked to the tasks was very comparable during exercise and rest. The results confirm that we can measure functional brain activity in real-time during low and moderate cycling exercise. We believe that incorporating physiological measures (e.g., heart rate, respiration) and refining data processing methods would further improve the utility of NIRS even at higher intensities of exercise, thus widening its application during exercise.
This means we can use NIRS to directly measure and compare the effects of exercise upon brain activity during, as well as following, exercise in healthy and clinical groups. For example, in our current work we are examining the effects of moderate-intensity cycling exercise on brain function in children with and without attention deficit/hyperactivity disorder (ADHD). Using NIRS, we have the potential to better understand brain mechanisms underlying changes in cognition and behavior resulting from exercise participation.
About the author:
Gavin D. Tempest, Ph.D., is an exercise neurophysiologist and researcher at Stanford University. His research examines the effect of exercise on brain function and behavior in children and adults. Dr. Tempest is an ACSM member (professional-in-training). This commentary presents his views on a topic related to a research article he co-authored with Allan L. Reiss, M.D., professor and director of the Division of Interdisciplinary Brain Research at Stanford University in California.