Background: Individuals with intellectual disability (ID) have very low physical activity and low peak oxygen uptake (VO[subscript 2peak]), potentially explained by physiologically lower peak heart rates (HR[subscript peak]). Method: The present authors performed a retrospective analysis of a large data set of individuals with intellectual disability (n = 100), with Down syndrome (DS) (n = 48) and without intellectual disability (n = 224) using multiple linear regression analyses, to determine if individuals with intellectual disability exhibit lower HR[subscript peak] and VO[subscript 2peak] than individuals without intellectual disability, controlling for age, sex and body mass index (BMI). Results: Individuals with intellectual disability on average have significantly lower HR[subscript peak] and VO[subscript 2peak] than individuals without intellectual disability, even when controlling VO[subscript 2peak] for the lower HR[subscript peak]. Conclusions: This study suggests potential physiological differences in individuals with intellectual disability and warrants further investigation to determine their relevance to physical activity promotion and exercise testing in individuals with intellectual disability.