Hot Topic: HIIT Improves and Sustains Cognitive Health Among Older Adults

By Machell Collier, MS
Senior Marketing and Clinical Content Specialist, IFM

Supporting brain and cognitive health through lifestyle-based approaches such as optimal nutrition, sleep, and exercise may be a healthy-aging priority for some patients or a core component of a personalized intervention for others. Increased physical activity and various exercise programs, from dance and mind-body exercises to aerobic and resistance training, have demonstrated significant health benefits, including improved cognition and overall brain fitness.^1-5 To further understand how specific forms of exercise may proactively protect against age-related cognitive decline, a new clinical trial investigated the effects of low, medium, and high-intensity interval training (HIIT) on hippocampal-related cognitive function in healthy older adults.⁶

HIIT Regimen Improves & Sustains Cognitive Health

The hippocampus is part of the brain responsible for short and long-term memory, spatial learning and memory, and emotional processing. The hippocampus has been shown to be vulnerable to aging, and studies suggest that a reduced hippocampal volume is closely related to cognitive impairment.⁷ Previous research has reported conflicting results about the impact of exercise on hippocampal volume, citing study design and the heterogeneity of type and length of exercise programs as potential areas for clarification.^8,9 A new randomized controlled trial, the 2024 Blackmore et al study, has now specifically investigated the impact of exercise at different levels of intensity on cognitive function, hippocampal-dependent spatial learning, and changes in hippocampal volume among healthy older adults (n=151 male and female healthy adults; average age of 72 years).⁶

Participants in the 2024 Blackmore et al study were randomly assigned to one of three interventions: low-intensity training (LIT), medium-intensity training (MIT), or HIIT.⁶ Over a six-month period, each participant exercised three times per week for a total of 72 supervised exercise sessions, and the LIT group served as the active control group. During each session, in addition to a ten-minute warm-up and a five-minute cool-down period, the different intensity levels completed the following exercise routines:⁶

• LIT group (45-55% peak heart rate (HR_peak): 30 minutes of five to eight stretching, balance, range of motion, and relaxation tasks.
• MIT group (60-75% HR_peak): 30 minutes of continuous treadmill walking at the target heart rate.
• HIIT group: 25-minute treadmill sessions of four, four-minute working periods at 85-95% HR_peak separated by three, three-minute active recovery intervals at 60-70% HR_peak.

Intensity levels were measured by personalized target heart rates, and monthly tests for cognitive function, hippocampal-dependent learning, and other cognitive domains were administered to monitor participants before, during, and following the exercise intervention. In addition to monthly blood samples, MRI brain scans were obtained for a subset of participants at the start and end of the intervention, as well as after another six months. Cognitive testing related to hippocampal performance continued for up to five years after the study. Among the results, researchers reported the following:⁶

• In the low and medium-intensity exercise groups, compared to baseline performance, hippocampal-dependent cognition was maintained during the exercise intervention and showed no age-related decline.
• Only the HIIT group showed significant improvement in hippocampal function and hippocampal-dependent spatial learning after the six-month exercise intervention. This improvement was retained up to five years after the exercise intervention compared to the low and medium-intensity exercise groups.
• At the end of the six-month intervention, MRI results indicated that the right-hand side hippocampal volume remained stable in the HIIT group but decreased significantly in both other exercise groups. All groups showed a significant decrease in volume for the left-hand side hippocampus.
• After six months of HIIT, significant increases in resting-state functional connectivity (i.e., brain region and network interactions) were reported compared to low and medium-intensity training.
• Both MIT and HIIT produced a similar increase in the circulating levels of brain-derived neurotrophic factor (BDNF).

Researchers acknowledged limitations of this study, including not having a sedentary, non-exercise control group and only including physically healthy individuals capable of participating in a six-month exercise intervention.⁶ From their study’s results and for the studied population, researchers did suggest that among healthy older adults, exercise programs that include HIIT may be appropriate and effective for the improvement of hippocampal-dependent cognitive function.⁶

Studies continue to investigate and reveal how exercise and other lifestyle-based factors impact cognition and brain structure and how results from the research field may best translate into practical clinical applications. Within the functional medicine framework, practitioners collaborate with patients to develop personalized therapeutic strategies that are most beneficial to their current conditions and concerns. For patients with cognitive issues and those concerned about brain-aging, personalizing a comprehensive health strategy that may include multiple lifestyle-based approaches, including appropriate exercise prescriptions, is part of a functional medicine approach to optimizing brain health.