Inclusion Criteria:  those who can follow simple commands and walk independently with or without the use of an assistance apparatus (within Classification level I-III, based on Gross Motor Functioning Classification System, GMFCS) and have cerebral palsy will be included in the study. The rationale for such inclusion criteria (level I-III) is to make sure they can perform some leg exercise and tests.  Exclusion Criteria:  If subjects have a history or symptoms of cardiovascular, renal, hepatic, or respiratory diseases, they will be excluded in the study.