The study is about the effect of an exercise program using stationary bicycling for children with the spastic diplegic form of cerebral palsy. Spastic diplegia is a type of cerebral palsy that involves spasticity or "tightness" of the leg muscles. We hope to learn whether this type of exercise will allow the children to develop improved strength in the muscles that bend and straighten their knees, enhance their level of physical fitness, improve their ability to walk and improve their ability to perform other activities that are important to them. We hypothesize that children who participate in the stationary cycling intervention will gain strength in the muscles that bend and straighten their knees, will be able to complete a 600 yard walk run test (a test of endurance) more rapidly, and will improve their score on a test of function called the Gross Motor Function Measure (a test designed specifically for children with cerebral palsy).

Inclusion Criteria:

• between the ages of 7 and 16 years and engaged in regular education as their primary academic path (children receiving resource help will not be excluded); - ability to follow simple verbal directions;
• good or fair selective motor control for at least one limb; and
• ability to walk independently, with or without assistive devices, for short distances. The lowest level of walking ability for inclusion is independent walking indoors but limitations outdoors and in the community, requiring the use of a wheelchair in these settings. These criteria for walking ability place subjects in Levels I-III of the Gross Motor Functional Classification System (GMFCS) (Palisano et al., 1997).

Exclusion Criteria:

• musculoskeletal or neurosurgical surgery or baclofen pump implantation within the past year;
• botulinum toxin injections within the past 6 months;
• serial casting or new orthotics within the past 3 months;
• initiating or increasing oral medications that affect the neuromuscular system, e.g. baclofen, within the past 3 months;
• onset of physical therapy, exercise, sport activity, or change in assistive devices for walking within the past 3 months;
• inability or unwillingness to maintain age appropriate behavior;
• serious medical conditions such as cardiac disease, diabetes, asthma, or uncontrolled seizures;
• current participation in a fitness program, that includes a cardiorespiratory endurance exercise, at least one time per week;
• significant hip joint contractures so that the hip cannot be passively moved throughout an excursion between 30 and 80 degrees;
• significant knee joint contractures so that the knee cannot be passively moved throughout an excursion between 40 and 110 degrees; and
• significant ankle joint contractures so that the ankle cannot be passively moved throughout an excursion of -10 to 20 degrees of plantarflexion. Exclusion criteria 8 - 10 are based on passive joint excursions necessary to perform stationary cycling (Ericson et al., 1988) allowing for some hip and knee joint compensation for subjects without ankle dorsiflexion range of motion.