Cardiorespiratory Fitness and Acute High-Intensity Exercise Effects on Brain and Cognitive Function in Older Adults (ExBrain)

July 21, 2026 updated by: Colby-Sawyer College

The goal of this clinical trial is to learn whether a single session of high-intensity interval exercise (HIIT) affects cognitive performance and brain activity in older adults, and whether cardiorespiratory fitness influences these effects. The main questions it aims to answer are:

  • Does a single HIIT session change performance on a task-switching test of cognitive flexibility?
  • Does a single HIIT session change prefrontal brain activity during cognitive testing, as measured by functional near-infrared spectroscopy (fNIRS)?
  • Do older adults with higher cardiorespiratory fitness show greater cognitive and brain changes in response to HIIT than those with lower fitness?

Participants will:

  • Visit the laboratory on two separate days
  • Complete a sub-maximal graded exercise test during the first visit to measure cardiorespiratory fitness
  • Complete a single ~30-minute HIIT cycling session during the second visit
  • Complete a task-switching cognitive test before and after the HIIT session
  • Have their brain activity monitored with fNIRS while completing the cognitive tests

Study Overview

Status

Not yet recruiting

Conditions

Intervention / Treatment

Detailed Description

Cognitive decline is one of the most consequential changes associated with aging, and executive functions-the set of higher-order cognitive processes that allow people to plan, adapt, and control their behavior-are especially susceptible to age-related change because they depend heavily on the prefrontal cortex, a brain region that shows some of the earliest and most pronounced structural and functional changes with age. Cognitive flexibility, the ability to shift rapidly between competing task rules or mental sets, is one specific executive function that supports many everyday activities, including driving, multitasking, and decision-making, and it can be measured experimentally using a task-switching paradigm that compares performance on trials requiring a rule switch to trials that repeat the same rule.

Physical exercise is increasingly recognized as a non-pharmacological approach that may help preserve cognitive and brain health in older adults, but the evidence on the acute (single-session) effects of exercise on cognition is inconsistent. Outcomes appear to depend on exercise intensity, duration, the timing of cognitive testing relative to exercise, the population studied, and the specific cognitive domain assessed. High-intensity interval training (HIIT)-brief, repeated bouts of vigorous exercise separated by recovery periods-produces strong cardiovascular, metabolic, and neuroendocrine responses in a short amount of time and has been associated with greater gains in cardiorespiratory fitness and cognition than continuous moderate-intensity exercise in some populations. However, one influential framework, the reticular-activating hypofrontality (RAH) model, proposes that intense physical exertion can temporarily divert neural resources away from the prefrontal cortex toward brain regions controlling movement and basic physiological regulation, which could transiently impair executive function immediately after high-intensity exercise. This model has rarely been tested directly in older adults using simultaneous brain imaging and cognitive testing, and it is not yet known whether an individual's cardiorespiratory fitness level protects against this kind of transient impairment.

This study is designed to address that gap by examining, within the same older adults, how a single bout of HIIT affects both performance on a task-switching test of cognitive flexibility and underlying prefrontal brain activity, and by testing whether cardiorespiratory fitness-measured on a continuous scale rather than as a simple high/low grouping-moderates these acute responses. Brain activity will be assessed using functional near-infrared spectroscopy (fNIRS), a non-invasive optical imaging method in which a sensor cap placed on the participant's forehead emits and detects near-infrared light to track relative changes in oxygenated and deoxygenated hemoglobin concentrations in the prefrontal cortex; increases in oxygenated hemoglobin coupled with decreases in deoxygenated hemoglobin are interpreted as increased regional brain activation. Compared with functional MRI, fNIRS is more portable, less expensive, and more tolerant of movement, while offering better spatial resolution than EEG, making it well suited for studying exercise-related brain responses in older adults.

Participants will attend two laboratory visits on separate days at the Exercise and Cognition Lab. The first visit establishes each participant's cardiorespiratory fitness and familiarizes them with study procedures: after health screening and baseline physical measures, participants will practice the task-switching paradigm on a laptop using PsychoPy® stimulus presentation software until their performance stabilizes, in order to minimize learning effects during the later experimental session. They will then complete a submaximal graded exercise test on a cycle ergometer, following a validated multistage protocol (American College of Sports Medicine submaximal cycle ergometer protocol) consisting of four consecutive 3-minute stages of progressively increasing workload. Heart rate and workload recorded during each stage are used to extrapolate, via the established linear relationship between heart rate and oxygen consumption, an estimate of maximal oxygen uptake (VO₂max) at the participant's age-predicted maximal heart rate, providing a safe and time-efficient index of cardiorespiratory fitness without requiring participants to exercise to true maximal exertion.

The second visit constitutes the experimental exercise session. After a health status check, participants will be fitted with the fNIRS sensor cap, positioned over prefrontal regions according to the standard EEG 10-20 placement system, and will complete the task-switching cognitive assessment while brain activity is recorded (pre-exercise timepoint). The fNIRS cap will then be removed and participants will complete the HIIT protocol on a cycle ergometer: four 4-minute bouts of high-intensity cycling, controlled to approximately 85-90% of individually determined maximal power output and heart rate, separated by 3-minute periods of passive or light active recovery. Heart rate, rating of perceived exertion, and pedaling cadence are monitored and recorded each minute throughout the exercise bout, and workload is adjusted as needed to keep participants within the prescribed intensity range; exercise may be modified or stopped at the study team's discretion based on participant signs or symptoms. Heart rate throughout both visits is tracked continuously using a wearable optical heart rate sensor worn on the upper arm or forearm. Immediately after the exercise bout, participants are refitted with the fNIRS cap and repeat the task-switching assessment while brain activity is again recorded (post-exercise timepoint), allowing within-participant comparison of cognitive and prefrontal neural responses before versus immediately after a single session of high-intensity exercise.

Cardiorespiratory fitness values derived from the submaximal test will be examined as a continuous moderating variable in statistical models of the pre-to-post exercise changes in cognitive and brain outcomes, alongside relevant covariates such as age, sex, grip strength, and lean body mass, using repeated-measures and mixed-effects statistical approaches. This design allows the study to test not only whether HIIT produces measurable shifts in executive function and prefrontal activation immediately afterward, but also whether individual differences in fitness help explain who is more or less susceptible to such shifts.

This project builds on preliminary pilot work conducted by the same research team using a related experimental design, which demonstrated that the task-switching paradigm behaves as expected (slower responses on switch versus repeat trials) and that reliable, good-quality fNIRS signal can be obtained from older adult participants using this cap montage and analysis pipeline. Findings from this study are intended to clarify the neurocognitive mechanisms underlying acute responses to high-intensity exercise in older adults and to inform more precise, individualized guidance on how and when high-intensity exercise might be safely incorporated into the daily routines of older adults, including consideration of timing relative to cognitively demanding activities.

Study Type

Interventional

Enrollment (Estimated)

50

Phase

  • Not Applicable

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Contact

Study Locations

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

  • Adult
  • Older Adult

Accepts Healthy Volunteers

Yes

Description

Inclusion Criteria:

  • Physical active in the last three months (>3x/week of 30 minutes of moderate exercise)
  • To participate in the study, participants must answer "no" to all the Physical Activity Readiness questionnaire (PAR-Q) questions and have no signs and symptoms of cardiovascular, metabolic, and kidney diseases following the decision tree of the American College of Sports Medicine screening procedure.
  • Agree to have their data stored in a human performance database for future use. Agree to have their data stored in a repository per the requirement of peer-reviewed scientific journals, which may require data to be stored in a repository as a condition for publication. Such repositories are online databases, in which coded data is linked (no link to participants personally) to the journal article citation. Must read, understand, and sign the informed consent form.

Exclusion Criteria:

  • Use of illicit drugs, excessive alcohol, and/or performance-enhancing drugs.
  • Have any current orthopedic injury.
  • Have implanted medical devices.
  • Serious medical conditions limiting the ability to safety participate in either the PA interventions; these include dementia, symptomatic heart or vascular disease, severe hypertension, recent myocardial infarction, stroke, severe insulin-dependent diabetes mellitus, psychiatric disease, renal disease, liver disease or active cancer
  • Mini-mental examination score < 23

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

  • Primary Purpose: Basic Science
  • Allocation: N/A
  • Interventional Model: Single Group Assignment
  • Masking: None (Open Label)

Arms and Interventions

Participant Group / Arm
Intervention / Treatment
Experimental: HIIT session
All enrolled participants complete two laboratory visits. The first visit establishes cardiorespiratory fitness via a submaximal graded exercise test and familiarizes participants with the task-switching cognitive paradigm. The second visit is the experimental session: participants complete the task-switching assessment with concurrent fNIRS brain imaging immediately before and immediately after a single bout of high-intensity interval training (HIIT). Cardiorespiratory fitness is examined as a continuous moderator of pre- to post-exercise changes in cognitive and brain outcomes.
Behavioral: High-Intensity Interval Training
A single session of high-intensity interval training (HIIT) performed on a cycle ergometer, consisting of 4 bouts of 4 minutes of high-intensity cycling separated by 3 minutes of passive or light active recovery (total exercise session approximately 30 minutes, excluding warm-up and cool-down). High exercise intensity is individually prescribed and controlled at approximately 85-90% of each participant's maximal power output and maximal heart rate, both estimated from a submaximal graded exercise test (American College of Sports Medicine submaximal cycle ergometer protocol) completed during a prior laboratory visit. During the recovery intervals, participants cycle at a light workload (30-50% of maximum power output). Participants are asked to maintain a cadence of approximately 50-60 revolutions per minute throughout. Heart rate, rating of perceived exertion (RPE), and cadence are monitored and recorded every minute during the session by a trained study team member.

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Change in Cognitive Flexibility (Task-Switching Performance)
Time Frame: Immediately before (pre-exercise) and immediately after (post-exercise) a single HIIT session (approximately 40-45 minutes apart).
Changes in reaction time (milliseconds) switch cost, calculated as the difference in mean reaction time between switch trials and repeat trials, on a computerized numerical classification task-switching paradigm. Larger switch costs indicate poorer cognitive flexibility.
Immediately before (pre-exercise) and immediately after (post-exercise) a single HIIT session (approximately 40-45 minutes apart).
Change in Prefrontal Cortex Activation (fNIRS)
Time Frame: Immediately before (pre-exercise) and immediately after (post-exercise) a single HIIT session.
Relative changes (ΔμM) in oxygenated hemoglobin (HbO) and deoxyhemoglobin (HbR) concentrations in prefrontal cortex regions, measured via functional near-infrared spectroscopy (fNIRS) during task-switching performance. Increased HbO and decreased HbR reflects increased regional brain activation.
Immediately before (pre-exercise) and immediately after (post-exercise) a single HIIT session.

Secondary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Correlation Between Cardiorespiratory Fitness (VO₂max ) and Change in Cognitive Flexibility
Time Frame: Baseline (Visit 1) for VO₂max; pre- and post-exercise on Visit 2 (approximately 40-45 minutes apart) for switch cos
Correlation between estimated VO₂max (mL/kg/min), derived from the ACSM submaximal cycle ergometer test protocol, and the change in reaction time switch cost (milliseconds) on the computerized task-switching paradigm from pre- to post-exercise.
Baseline (Visit 1) for VO₂max; pre- and post-exercise on Visit 2 (approximately 40-45 minutes apart) for switch cos
Correlation Between Cardiorespiratory Fitness and Change in Prefrontal Cortex Activation
Time Frame: Baseline (Visit 1) for VO₂max; pre- and post-exercise on Visit 2 (approximately 40-45 minutes apart) for HbO/HbR
Correlation between estimated VO₂max (mL/kg/min), derived from the ACSM submaximal cycle ergometer test protocol, and the change in oxygenated hemoglobin (HbO) and deoxyhemoglobin (HbR) concentrations (ΔμM) in the prefrontal cortex, measured via fNIRS, from pre- to post-exercise.
Baseline (Visit 1) for VO₂max; pre- and post-exercise on Visit 2 (approximately 40-45 minutes apart) for HbO/HbR

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

Colby-Sawyer College

Collaborators

Tufts University

Publications and helpful links

The person responsible for entering information about the study voluntarily provides these publications. These may be about anything related to the study.

General Publications

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Estimated)

August 1, 2026

Primary Completion (Estimated)

July 1, 2027

Study Completion (Estimated)

August 1, 2028

Study Registration Dates

First Submitted

July 17, 2026

First Submitted That Met QC Criteria

July 21, 2026

First Posted (Actual)

July 27, 2026

Study Record Updates

Last Update Posted (Actual)

July 27, 2026

Last Update Submitted That Met QC Criteria

July 21, 2026

Last Verified

July 1, 2026

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

  • P20GM103506 (U.S. NIH Grant/Contract)

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

YES

IPD Plan Description

De-identified (coded) individual participant data will be deposited in a repository as required for publication in peer-reviewed journals. Data will be available to researchers upon reasonable request, consistent with participant consent for use in a human performance database for future research use.

IPD Sharing Time Frame

De-identified individual participant data, along with the study protocol, SAP, and analytic code, will be made available beginning at the time of associated publication, with no planned end date for availability

IPD Sharing Supporting Information Type

  • STUDY_PROTOCOL
  • SAP
  • ANALYTIC_CODE

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

No

Studies a U.S. FDA-regulated device product

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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