The goal of this clinical trial is to determine if radial Extracorporeal shockwave therapy (rESWT) reduces spasticity in children with Cerbral Palsy (CP) or traumatic brain injury (TBI). The main questions it aims to answer are:

• Is it feasible to implement radial shockwave therapy in conventional physiotherapy plan in children with CP or TBI?
• Is it safe and effective to use rESWT for reducing spasticity in children with CP or TBI? Participants will receive a 4 week therapy intervention, as add on to the conventional physio (usual care), including one rESWT session per week for a total of 4 sessions.

Inclusion Criteria:

• cerebral palsy or acquired brain injury
• between 6-18 years old;
• gross motor function classification ≥2;
• experiencing spasticity in the lower limb (calf muscles, hip adductor muscles or hamstring muscles) and/or in the upper limb (biceps muscle, wrist flexor muscles, finger flexor muscles) with Modified Ashworth Scores (MAS) ≥1+.

Exclusion Criteria:

• recent (≤3 months) Botox injections or other recent (≤6 months) invasive intervention;
• local infections or wounds; neuropathy;
• severe organ dysfunction;
• severe psychosocial dysfunction that would not allow adhering to protocol;
• planned changes in medication dosage or medication scheme that might affect spasticity during a 4-month intervention and follow-up phase.