Rationale: Children with cerebral palsy (CP) experience limitations in walking ability due to functional motor impairments caused by neurodevelopmental damage during fetal or early child development. Due to these motor impairments, children with CP struggle to keep up with typically developing peers when participating in physical and/or social activities. Consequently, the development of these children may be hampered. Recently, functional power training (FPT) emerged as a potentially successful supplementary treatment method to improve participation in children with CP. It is understood that FPT is more effective than progressive resistance training in improving walking ability and endurance, and thereby better supports participation in ambulatory children with CP. Nevertheless, high-level scientific evidence underpinning the efficacy of FPT on these parameters in ambulant children with CP is still lacking. The investigators hypothesize that FPT effectively helps accomplish patient-tailored participation and activity goals in ambulant children with CP.

Objective: This study aims to investigate whether twelve weeks of FPT (MegaPower training) effectively accomplish patient-tailored participation and activity goals in ambulant children with CP, when compared to their usual care. Additionally, the goal is to investigate i) whether MegaPower training improves walking ability, aerobic endurance, and anaerobic capacity; ii) what factors best identify which ambulant children with CP benefit most from twelve weeks of MegaPower training; iii) to what extend the MegaPower training was implemented as intended in the participating study centers?, and iv) whether the effects of the MegaPower training are maintained after 12 and 24 weeks of follow-up.

Study design: A single-blind randomized controlled parallel trial with a 24 week follow-up. During the follow-up, the control group will also receive MegaPower training.

Study population: Ambulant children with cerebral palsy or a related non-progressive disorder between the ages of 4 - 12.

Intervention: One group will receive twelve weeks of FPT (MegaPower training), whilst the other group will receive twelve weeks of usual care (control group).

Main study parameters/endpoints: Accomplishment of patient-tailored participation and activity goals, measured through Goal Attainment Scaling.

Children with cerebral palsy (CP) experience limitations in walking ability due to functional motor impairments caused by neurodevelopmental damage during fetal or early child development that may result in spasticity, dyskinesia, or ataxia. Due to these motor impairments, children with CP struggle to keep up with typically developing peers when participating in physical and/or social activities. Yet, participation is a key factor in child development, mainly because it is instrumental in enhancing mental well-being through building friendships, developing a personal identity, optimizing physical growth, and increasing motor control. Earlier studies concluded that children with CP are indeed at an elevated risk for reduced physical activity and participation. Consequently, the development of these children may be hampered. Therefore, targeted interventions that increase physical activity and participation are essential for supporting the general development of children with CP. A large number of treatments have been developed for children with CP, ranging from pharmacological agents that manage tone to invasive surgical interventions. Whilst many of these treatments effectively improve motor control, very few address the underlying fatigue that is typically seen in these children, which causes a vicious cycle of reduced physical fitness, early onset of fatigue, and decreased physical activity levels. This decline in physical fitness is ultimately detrimental to participation, and therefore a wide variety of exercise-related treatment options are being explored to improve motor control, physical fitness, and participation.

Recently, functional power training (FPT) emerged as a potentially successful supplementary treatment method to improve participation in children with CP. This type of strength training combines high velocity movements with progressive resistance to mimic and train the demands of playing activities like playground running and sprinting in games and sports. Indeed, a previous double-baseline study indicated that FPT improves physical fitness, muscle strength, activity, and participation in ambulatory children with CP. This is unlike progressive resistance training (PRT), which increases muscle strength but not walking ability, anaerobic capacity, and ultimately participation. This discrepancy is likely explained by the functional nature of FPT, which specifically trains activities of daily living and not only muscle strength. Moreover, power training may be more effective than strength training as power training incorporates high intensity, explosive-like contractions that are required in daily living situations. Consequently, FPT is more effective than PRT in improving walking ability, thereby better supporting participation in ambulatory children with CP. Nevertheless, high-level scientific evidence underpinning the efficacy of FPT on walking ability, aerobic endurance, anaerobic capacity, and participation in ambulant children with CP is still lacking. Furthermore, it remains unclear what predictive factors best identify which children with CP benefit most from FPT. Additionally, it remains unknown whether the potential benefits of FPT on walking ability, aerobic endurance, anaerobic capacity, and participation in children with CP are maintained when FPT is discontinued.

Inclusion Criteria:

• Children with cerebral palsy or a related non-progressive disorder between the ages of 4 to 12.
• Gross Motor Function Classification System (GMFCS) level I - III.
• Parents and/or children have a treatment question related to participation of the child.

Exclusion Criteria:

• Participants that suffer from a progressive neurological disorder.
• Treatment with botulinum toxin and/or serial casting in lower extremities planned during the study period.
• Treatment with botulinum toxin in the twelve weeks prior to participation in the study.
• Treatment with serial casting in the three weeks prior to participation in the study.
• Children that underwent a selective dorsal rhizotomy twelve months prior to participation in the study.
• Children that underwent orthopedic surgery on their lower extremities in the 12 months before participation in the study.
• Children that have received MegaPower training in the last 4 months before participation in the study.
• Children for whom walking is not their preferred method of locomotion (yet).