Inclusion Criteria:  aged 5 years to 19 years typically developing with no diagnosed medical conditions that affect movement, OR with a diagnosis of bilateral cerebral palsy (including diplegia, tetraplegia, and quadriplegia) where the lower limbs are more affected than the upper limbs ability to independently step up, with or without assistive devices.  Exclusion Criteria:  lower limb surgery in the past year botulinum toxin injections to the lower limb muscles in the past 6 months cognitive dysfunction that would make following directions difficult comorbidities that would make participation unsafe.