Aim Lack of muscle growth relative to bone growth may be responsible for development of contractures in children with cerebral palsy (CP). Here, we used ultrasonography to compare growth of the medial gastrocnemius muscle in children with and without CP. Method Twenty‐six children with spastic CP (15 males, 11 females; mean age 35mo, range 8–65mo) and 101 typically developing children (47 males, 54 females; mean age 29mo, range 1–69mo) were included. Functional abilities of children with CP equalled levels I to III in the Gross Motor Function Classification System. Medial gastrocnemius muscle volume was constructed from serial, transverse, two‐dimensional ultrasonography images. Results In typically developing children, medial gastrocnemius volume increased linearly with age. Among children with CP, medial gastrocnemius volume increased less with age and deviated significantly from typically developing children at 15 months of age (p<0.05). Bone length increased with age without significant difference (p=0.49). Interpretation Muscle growth in children with CP initially follows that of typically developing children, but decreases at 15 months of age. This may be related to reduced physical activity and neural activation of the muscle. Interventions stimulating muscle growth in young children with CP may be important to prevent contractures.

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Reduced depression of transmitter release from Ia afferents following previous activation (post-activation depression) has been suggested to be involved in the pathophysiology of spasticity. However, the effect of this mechanism on the myotatic reflex and its possible contribution to increased reflex excitability in spastic participants has not been tested. To investigate these effects, we examined post-activation depression in Soleus H-reflex responses and in mechanically evoked Soleus stretch reflex responses. Stretch reflex responses were evoked with consecutive dorsiflexion perturbations delivered at different intervals. The magnitude of the stretch reflex and ankle torque response was assessed as a function of the time between perturbations. Soleus stretch reflexes were evoked with constant velocity (175 degrees /s) and amplitude (6 degrees) plantar flexion perturbations. Soleus H-reflexes were evoked by electrical stimulation of the tibial nerve in the popliteal fossa. The stretch reflex and H-reflex responses of 30 spastic participants (with multiple sclerosis or spinal cord injury) were compared with those of 15 healthy participants. In the healthy participants, the magnitude of the soleus stretch reflex and H-reflex decreased as the interval between the stimulus/perturbation was decreased. Similarly, the stretch-evoked torque decreased. In the spastic participants, the post-activation depression of both reflexes and the stretch-evoked torque was significantly smaller than in healthy participants. These findings demonstrate that post-activation depression is an important factor in the evaluation of stretch reflex excitability and muscle stiffness in spasticity, and they strengthen the hypothesis that reduced post-activation depression plays a role in the pathophysiology of spasticity.

AIM Clinical determination of spasticity is confounded by the difficulty in distinguishing reflex from passive contributions to muscle stiffness. There is, therefore, a risk that children with cerebral palsy (CP) receive antispasticity treatment unnecessarily. To investigate this, we aimed to determine the contribution of reflex mechanisms to changes in the passive elastic properties of muscles and tendons in children with CP.METHOD Biomechanical and electrophysiological measures were used to determine the relative contribution of reflex and passive mechanisms to ankle muscle stiffness in 35 children with spastic CP (21 males, 14 females; mean age 9y, SD 3y 4mo; range 3-15y) and 28 control children without CP (19 males, nine females; mean age 8y 11mo, SD 2y 10mo; range 3-15y). Twenty-seven children were diagnosed as having spastic hemiplegia, six with spastic diplegia, and two with spastic tetraplegia. According to the Gross Motor Function Classification System, 31 children were classified in level I, two in level II, and two in level III.RESULTS Only seven children with spastic CP showed reflex stiffness outside the range of the control children. In contrast, 20 children with spastic CP showed abnormal passive muscle stiffness (p<0.001). No correlation between increased reflex or increased passive muscle stiffness and age was observed within the age range studied.