Cerebral palsy (CP) has a prevalence of 1.5-3 per 1000 live births, making it the most common neurological disorder among children in Europe. One of the most frequently observed problems in CP is hypertonia, i.e. increased muscle tension, which can result in contractures. Stretching therapies are widely used as a treatment for contractures, but with highly variable success. Therefore, efforts are needed to improve the efficacy of stretching interventions. The investigators hypothesise that increasing the stiffness of the tendon relative to the muscle, by resistance training, prior to stretching will improve the efficacy of stretching interventions in children with CP. In a RCT design the investigators will compare a group of children receiving a combined strengthening-stretching intervention of the calf muscle to a control group receiving conventional stretching exercises in combination with upper limb exercises. Outcome measures will include muscle-tendon structure and gait analysis to assess functional improvements. This research will improve the understanding of muscle responses to stretching interventions in children with CP and can lead to more effective stretching therapies.

Cerebral palsy (CP) is a disorder resulting from a non-progressive lesion in the brain during pregnancy or early childhood. Children with CP show impaired movement patterns compared to typically developing (TD) children. One of the main factors limiting movement in children with CP is a reduced range of motion (ROM), which can be caused by a combination of neural and mechanical factors. Mechanical factors contributing to a reduced ROM are increased muscle/fascicle stiffness, reduced muscle length and changes in intramuscular tissue properties, all of which contribute to contractures.

Contractures are conservatively treated with stretching therapies, e.g., casting, night splints and physical therapy. However, they are very demanding for both children and parents, especially physical therapy which is painful and time-consuming. Therefore, when recommending stretching therapies, we need to assure they are efficacious. However, recent reviews show that the outcomes of stretching therapies in children with CP are highly variable.

Stretching interventions aim to improve ROM motion by increasing the overall length and/or lengthening properties of the muscle. To successfully achieve these adaptations, the muscle must experience adequate tensile stimulus during the intervention. However, it has been shown by previous studies examining muscle behaviour during stretch, that the muscle and fascicles in children with CP lengthen less than in TD children. Our own studies have confirmed this observations at the muscle, but also shown that the tendon in children with CP lengthens more during a stretch, than in TD children. These observations indicate that the higher stiffness of the target muscle relative to the in series tendon prevents the muscle fibres to experience a sufficiently large stretching stimulus, and the adaptations are small. Accordingly, in a recent study on long term stretching interventions it has been shown that muscle and fascicle strain increase, but no changes in the muscle's resting length or functional improvements have been found.

If you were to increase the stiffness of the tendon relative to the muscle prior to the stretching intervention, a greater stretching stimulus could be provided to the muscle. This would mean that for any given joint stretch the muscle will experience a greater portion of the stretch. It is well established in healthy adults and children that the stiffness of the tendon increases following resistance training. Given that well-designed resistance training is effective and safe for children with CP, the same increased tendon stiffness should follow gains in muscle strength in this group too. It is therefore hypothesise that a combined strengthening-stretching intervention would stiffen the tendon, increase the amount of stretch seen by the muscle, and thereby improve the effectiveness of stretching interventions.

Inclusion Criteria:

• Diagnosed with spastic cerebral palsy
• GMFCS level I-III
• Have the ability to perform at least one bi-lateral heel raise.
• Aged 7 to 14

Exclusion Criteria:

• Orthopaedic or neural surgery to the lower limb 2 years prior to or planned during the intervention
• Botulinum Toxin A injections 6 months prior to or planned during the intervention.
• A learning or behaviour impairment that prevents full participation in the intervention.