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

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

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