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

Children born prematurely are at risk of brain injury that can result in cerebral palsy(CP), most often affecting the legs, called spastic diplegia. Current treatment is largely passive, including leg braces, repeated injection of a paralyzing agent (Botox) 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 with mammals show that early brain injury can be alleviated by intensive exercise therapy, but only while the animal is very young. Building on the success with early, intensive therapy for children with perinatal (around birth) stroke, the investigators will apply intensive therapy for the legs in children with diplegia. Children (8 mo - 3 yr old) will be randomly assigned to start treatment immediately or delay treatment for 3 mo. The delay period controls for improvement without treatment. These children will also receive treatment after the delay period. The therapy will be guided by physical therapists, and similar to the project on perinatal stroke. Children who live beyond commuting distance from the centres will form a 3rd group, whose parents will be coached by therapists to train the child at home. This group will show whether parents can be as effective as a therapist. Finally, when all children turn 4 yr old, they will be compared to other 4-yr-old children with the same diagnosis, but no training, to determine if there are long term benefits. The investigators anticipate that like the children with perinatal stroke, early intensive exercise will improve mobility, facilitate earlier and better walking, and that the effects will be enduring.

Inclusion Criteria:

• children aged 8 mo - 3 yr old
• Evidence of periventricular white matter injury on diagnostic imaging
• clinical evidence of spastic diplegia

Exclusion Criteria:

• born before gestational age of 25 weeks
• birth weight <1000g (to exclude confounds related to extreme prematurity and low birth weights)
• MRI evidence of diffuse injury to the cerebral or cerebellar cortex
• uncontrolled epilepsy or infantile spasms in the past 6 months (contraindication for TMS)
• cardiovascular or musculoskeletal complications that preclude participation in intensive exercise
• Botulinum toxin (BTX-A) injections in the last 6 months
• Predicted GMFCS 4 or 5