Clinical, Biomechanical, Histo-immunological and Radiological Characterization of the Effects of Two Gastrocnemius Stretching Programs in Adult Patients With Spastic Paresis Following Cerebral Palsy: MYOSPAS-CP, a Randomized Controlled Study

Cerebral palsy (CP), resulting from a perinatal central neurological lesion, leads not only to lifelong motor impairment but also to a specific muscular disorder: spastic myopathy. This condition is characterized by early and progressive structural changes including decreased passive extensibility (XV1), reduced muscle fiber diameter, decreased number of sarcomeres in series, and hypertrophy of the endomysium and perimysium. In children, impaired gastrocnemius growth-quantified by reduced medial gastrocnemius muscle volume-appears before age 3 and precedes both hyperactivity and fixed stiffness. However, the long-term consequences of decades of underuse on the mechanical, histological, and morphometric properties of the gastrocnemius in adults with IP remain insufficiently explored.

Stretching, although widely prescribed, lacks standardized parameters, and its long-term effectiveness in adults with IP has never been formally evaluated. Evidence suggests that muscular plasticity requires high-load stretching and ≥10 minutes per muscle per day. Preliminary studies using Guided Self-Rehabilitation Contracts (GSCs) demonstrated significant gains in extensibility and function, while a randomized controlled trial in adults with acquired hemiparesis showed increased fascicle length, increased muscle thickness, and improved gait speed after one year of high-load self-stretching, supporting the reversibility of molecular pathways driving contracture.

This single-blind randomized controlled trial includes 40 adults with IP, randomized to: (1) conventional physiotherapy alone, or (2) conventional physiotherapy + a one-year daily GSC-based high-load gastrocnemius self-stretching program (10 minutes/day + phasic maximal dorsiflexion efforts). Multi-scale assessments span six analytical domains: clinical measures (XV1, XV3, XA; gait speed; SF-36), in vivo tissue biomechanics (resistance torque, passive energy, fascicle length, muscle thickness), functional and neurophysiological biomechanics (agonist-antagonist recruitment during gait), MRI morphometry (volume, intramuscular fat, edema), in vitro biomechanics (compressibility, strain, rupture stress), and genetic/histological markers (satellite cells, expression profile of 57 myogenic genes). Micro-invasive biopsies of both limbs will be performed at J1 and M12.

The primary outcome is maximal barefoot 10-meter gait speed. Secondary outcomes will characterize, chronologically and mechanistically, the trajectory of spastic myopathy and the potential of long-term high-load stretching to partially reverse its pathogenic processes.