Influence of Immobilization, Stretching, and Activity on the Morphological Properties of Spastic Gastrocnemius Muscles

<b>Background/Objectives:</b> Children with cerebral palsy (CP) often develop altered muscle architecture and calf muscle contractures. Orthotic immobilization aims to provide prolonged stretch to lengthen the muscle belly and muscle-tendon unit (MTU), but immobilization may also cause atrophy. This study investigated whether immobilization combined with periods of daily muscle activation has a different effect on calf muscle properties than continuous immobilization alone. <b>Methods</b>: Fourteen children with CP and equinus deformity (mean age: 9.9 ± 3.0 years; GMFCS Level I: 10, II: 4) were enrolled in a 12-week randomized controlled trial. Participants were allocated to one of two groups: continuous immobilization (23 h per day) with a dynamic ankle-foot orthosis (AFO), or a combined regimen consisting of immobilization (14 h) and a daily activity phase (10 h). Gastrocnemius medialis (GM) MTU properties, including muscle belly and Achilles tendon (AT) length, fascicle length, and muscle volume, among others, were assessed four times using three-dimensional (3D) freehand ultrasound. <b>Results</b>: Significant within-group increases in MTU and AT lengths were observed over time at both a 90° ankle position (<i>p</i> < 0.01) and a more dorsiflexed ankle position (4 Nm applied torque, <i>p</i> < 0.01). However, no significant group × time interactions were observed for any parameter. <b>Conclusions</b>: Contrary to our hypothesis, combining activity and immobilization did not confer additional benefits. Nevertheless, shorter orthosis-wearing time had the same effect on the MTU and could lead to improved compliance with orthosis treatment in CP. Larger trials are needed to support our findings.