This is a randomized controlled trial, comparing 3 months of intensive leg exercise to standard physiotherapy care for the improvement of gross motor function in young children with spastic diplegia.

Children born prematurely are at risk of brain injury that can result in cerebral palsy, most often affecting both legs. Current treatment is largely passive, including leg braces, repeated injection of a paralyzing agent (botulinum toxin) in muscles that are abnormally active, and surgery as deformities occur. Active, physical therapy for weak muscles is infrequent, occurring twice a month or less. Yet, recent work in mammals show that early brain injury can be alleviated by intensive exercise therapy, but only while the animal is very young.

Building on our success with early, intensive therapy for children with perinatal stroke, we will apply intensive therapy for the legs in children with cerebral palsy involving both legs. Children (8 mo - 3 yr old) will be randomly assigned to start treatment immediately or delay treatment for 6 months. The delay period controls for improvement without treatment. The children in the Delay Group will have the option to receive the same treatment after the delay period. The therapy will be guided by physical therapists, and centered on play. Measures will be taken before, during and after the delay and treatment periods. Measures will include clinical scores of motor development, proficiency of walking, participation at home, and physiological measures of motor and sensory function. All children will be followed until they turn 4 yr old, to determine if there are long term benefits. The cost-effectiveness of the intervention will be evaluated by a health economist. We anticipate that early intensive exercise will improve mobility, facilitate earlier and better walking, and that the effects will be enduring.

Inclusion Criteria:

• Bilateral motor impairment of the lower extremities
• Periventricular white matter injury from encephalopathy of prematurity
• Able to stand with some support

Exclusion Criteria:

• Substantial upper extremity involvement - Manual Abilities Classification System (MACS) Level ≥3
• Uncontrolled epilepsy or infantile spasms in the past 6 months
• Cardiovascular or musculoskeletal complications that preclude participation in intensive exercise
• Botulinum toxin-A (BTX-A) injections in the legs in the last 6 months

Physical therapy assessors will be blinded to the child's group assignment.