This study will investigate the effect of a 6-week stretching intervention, consisting of a combination of a 2-week casting period and a home-based stretching program of the plantar flexors and hamstrings, on muscle and tendon lengths, range of motion, stiffness, and functional muscle strength. The study will include patients with spastic cerebral palsy aged between 4 and 11 years old with a Gross Motor Function Classification Score (GMFCS) level between I and III.

This study will investigate the effect of a 6-week stretching intervention on muscle and tendon lengths, range of motion, stiffness, and functional muscle strength. The program consists of a 2-week casting period of the lower legs and a home-based stretching program of the hamstrings, followed by a 4-week stretching program of both the plantar flexors and hamstrings.

The aim is twofold: (1) determine whether a 6-week stretching program for the plantar flexors and knee flexors leads to changes in the morphological muscle and tendon properties of the medial gastrocnemius and semitendinosus, ankle and knee range of motion, muscle strength, gait and gross motor function; and (2) determine the correlation between baseline morphological muscle and tendon properties and the changes in the primary outcome parameters (ankle range of motion and stiffness).

The program will start with a 2-week period of stretching casts for the ankle plantar flexors, combined with a passive stretch program for the hamstrings, followed by a passive and active stretch program for both muscle groups for the remaining 4 weeks. The durations and frequencies for passive and active stretching are based on guidelines published by our own research group and on programs applied by previous research. The program will be set-up as a supervised home-based program on top of the usual care. The morphological muscle and tendon parameters, strength, spasticity, stiffness as well as gross motor function will be assessed before and after the entire 6-week stretching program. At the time of cast removal (after 2 weeks), only the morphological muscle and tendon parameters will be evaluated.

This study includes an intervention and control group which will be group-matched based on diagnosis, GMFCS level and age. The study will include patients with spastic cerebral palsy between 4 and 11 years old and a GMFCS level between I and III. Thirty children with a clinical indication for casting of the lower limb will be included in the intervention group and 30 children without an indication for a specific intervention will be included in the control group. Children in the control group will continue their usual care or normal routine treatment, i.e. physiotherapy and orthotic devices.

Inclusion Criteria:

• Confirmed diagnosis of spastic cerebral palsy
• Aged 4-12 years
• GMFCS levels I-III (GMFCS = Gross Motor Function Classification Score, expressing the overall functional level of impairment)
• Sufficient cooperation to comprehend and complete the test procedure
• Indication for casting of the lower limb

Exclusion Criteria:

• Non-ambulatory
• Botulinum toxin A injections six months prior to enrollment
• Lower limb surgery two years prior to enrollment
• Selective dorsal rhizotomy as treatment history
• Presence of ataxia or dystonia
• Cognitive problems that impede measurements
• Severe co-morbidities (severe epilepsy, non-correctable visual impairment, autism spectrum disorders, mental problems that prevent comprehensiveness of the tasks)