--- - |2+ Background Individuals with intellectual disability (ID) have very low physical activity and low peak oxygen uptake (VO2peak), potentially explained by physiologically lower peak heart rates (HRpeak). 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 HRpeak and VO2peak than individuals without intellectual disability, controlling for age, sex and body mass index (BMI). Results Individuals with intellectual disability on average have significantly lower HRpeak and VO2peak than individuals without intellectual disability, even when controlling VO2peak for the lower HRpeak. 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. - Journal of Applied Research in Intellectual Disabilities, Volume 31, Issue 5, Page 785-791, September 2018.