PURPOSE: Obesity in Down syndrome (DS) is a very commonhealth condition. Individuals with DS show low cardiovascular function such aslow peak heart rate (HR peak) and peak oxygen consumption (VO2peak). It isunknown if obesity affects HR peak and VO2peak in this population. PURPThe purpose of this study was to investigate the effects of DS, Intellectual disability (ID) and obesity on determinants of exercise performance, such as peak heart rate (HR peak) and peak oxygen consumption (VO2peak) in children and adults.METHODS: 425 adults, 100 with ID, 77 with DS, 248 controls,as well as 165 children, 83 with DS, and 82 with ID participated in this study. Each participant performed a maximal walking treadmill test, with VO2 and HR measurements. Analysis of variance (ANOVA) and Analysis of covariance (ANCOVA) were used to analyze the data.RESULTS: (See table) Obese adults exhibited significantly lower VO2peak and HRpeak compared to their nonobese peers in all groups (p<.05). Conversely, in children with DS, obesity had no effect on HRpeak and less impact on VO2peak than in children with ID. Obese children with ID had lower HRpeak and VO2peak than their nonobese peers (p<.05).CONCLUSIONS: The results suggest that obesity impacts HRpeak and VO2peak differently in children with DS than in children with ID or in adults with or without DS. This may imply that obesity is associated with autonomic dysfunction in children with ID and in adults regardless of group, but not in children with DS.