Children with Autism Spectrum Disorder (ASD) have impaired communication, social, and behavioural skills. Research shows that they are also less physically fit than other children. Yet, the fitness measures used in these studies have not been proven to be suitable for children with ASD. Therefore, the possibility of measurement error complicates both the interpretation of these results and the planning of future research. The focus of this research is on establishing the most reliable and valid measures of physical fitness in 8-10 year old children with ASD; assessing the fitness of children with ASD in comparison to a matched control group of typically developing peers; and facilitating the design and implementation of clinical- and community-based physical health interventions for children with ASD. Study 1 will assess the feasibility, reliability, and construct validity of seven different test of physical fitness to determine which test(s) are best suited for 8-10 year old children with ASD. Study 2 will compare the fitness levels of 8-10 year old children with ASD with a matched control group of typically developing children to determine any differences. Results from the first two studies will facilitate the design and implementation of a physical health intervention for 8-10 year children with ASD and assess the effect of the intervention on numerous health and behavioural outcomes (Study 3). This novel program of research will have a positive impact on the health and well-being of children with ASD and will make a significant contribution to the literature. Funding this program of research will also highlight the importance of this work and will place Canadian research at the forefront of pediatric exercise science research for children with ASD.