Intellectual disability (ID) is a neurodevelopmental disorder accompanied by sedentary lifestyles, which worsens cognitive function and physical health. Short-duration high-frequency exercise snacks (ES) may be a feasible intervention for adults with ID. This randomized controlled crossover study aims to explore the acute effects of exercise snacks, conventional HIIT and daily routine control on cognitive function, stereotyped behaviors and prefrontal cortex activation in adults with mild to moderate ID. All participants will receive three intervention conditions with a 1-week washout period between each trial. Neurophysiological indicators including EEG and heart rate variability will be measured to reveal the underlying mechanisms.