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