Cerebral palsy (CP) is the most common brain injury in the pediatric population. CP patients present different affectations such as decreased muscle strength, gait deviations, impaired proprioception, and spasticity. Isokinetic strengthening programs combined with an intensive rehabilitation may improve muscle strength and therefore gait efficiency. Clinical Trials: The protocol has been accepted by the French National Ethics Committee (IDRCB: 2022-A00431-42). The primary aim of this randomized controlled trial is to compare the effect of an intensive rehabilitation combined with a non-functional isokinetic progressive strengthening program to an intensive rehabilitation alone on gait parameters and muscle strength in CP patients. Another goal of the current study is to determine whether adding an isokinetic program to an intensive rehabilitation is more effective than an intensive reha-bilitation alone on decreasing spasticity and improving joint position sense in CP patients. Thirty adolescents with spastic diplegia CP (GMFCS level I to III) will be randomized, by an independent researcher, into a 3-week intensive rehabilitation and isokinetic pro-gressive strengthening group or an intensive rehabilitation control group. Gait param-eters, muscle strength, spasticity and knee joint position sense will be assessed. These variables will be evaluated at baseline (T0) and at the end of the intervention (T1). The intensive rehabilitation will consist of physiotherapy sessions twice a day and hydro-therapy and virtual reality gait training once a day. The isokinetic training group will have a total of 9 supervised isokinetic strength training focusing on knee flexors and extensors with different execution speeds. The protocol has been accepted by the French National Ethics Committee in October 2022. Inclusion of patients will start in November 2022. The combination of an intensive rehabilitation with an isokinetic program on knee flexors and extensors have not been studied yet. The findings of this study may determine if an isokinetic strength training program of knee flexors and extensors is benefic to improve gait parameters, muscle strength, spasticity, and joint position sense in adolescents with spastic diplegia. The protocol has been accepted by the French National Ethics Committee (IDRCB: 2022-A00431-42).