Children with autism spectrum disorders (ASD) frequently have some physical limitations. They may have problems with gross motor skills, those needed for large-scale activities, such as walking, running or jumping.
A number of other symptoms of autism can also interfere with a child with ASD ability or desire to participate in physical activities. Sensory sensitivities may make it challenging for some. Others may find that developmental difficulties in planning and organization make it hard to complete physical tasks.
Physical activity, however, is important for social and developmental reasons and recent research has shown that almost 20 percent of children with autism are overweight and another 36 percent are at risk for being overweight. While medications and genes may play a part, the lack of physical activity is also seen as a contributing factor.
Eric Chessen, author of Autism Fitness, explains that many exercises, although easily adapted for children with ASD are not conducive to helping because fitness programs do not "focus on long-term fitness development for children, adolescents and young adults with autism. As a result, the movement deficits or imbalances that occur in infancy continue to persist into later stages of life." 
Exercise and physical activity has been found, in some research, to improve symptoms of autism. Although it is not recommended that exercise replace traditional therapies, it can help to enhance these therapies. Additionally, exercise and sports programs offer social benefits, increase self-esteem and has been shown to increase feelings of well-being.
To start an exercise program, Chessen suggests the following:
Start with basic activities:
- Pushing - throwing medicine balls, pushups
- Pulling - climbing, pulling with an exercise band
- Bending - squatting, picking up weighted objects, bear walks, frog hops
- Rotation - pivoting steps, throwing balls while twisting
- Locomotion - short runs, hopping
Based on your child's abilities continue progressing through different activities or simplify the exercises to fit his or her individual abilities
Use activities your child enjoys as a motivation to engage in physical activity, for example, you might want to do jumping jacks and then listen to a favorite song
Be specific with praise. Instead of a general "good job" notice and compliment specific actions.
Keep instructions simple.
Create a family exercise time and incorporate exercise into different activities to make it part of daily life.
"Sports, Exercise and the Benefits of Physical Activity for Individuals with Autism," 2009, Feb 19, Geraldine Dawson, Michael Rosanoff, Autism Speaks
 "Top 8 Exercises for Autism Fitness," 2009, Eric Chessen, AutismFitness.com