During the past 30 years spasticity research has raised fundamental concerns regarding the definition, evaluation and functional significance of spasticity. The present thesis is a direct continuation of this work. The aim of the thesis was to evaluate reflex mediated stiffness (spasticity) and passive stiffness (changes in the elastic properties of muscles) of ankle joint muscles at rest, during gait and in relation to gait training in children with cerebral palsy (CP). In study I we found that reflex mediated stiffness is difficult to distinguish clinically from changes in passive muscle stiffness and notably that passive muscle stiffness rather than increased reflex stiffness (spasticity) is the most frequent explanation of ankle muscle hyper tonicity in children with CP. These findings emphasises the importance of properly distinguishing different contributions to muscle stiffness in order to avoid unnecessary antispastic treatment.

Findings from study II suggested that spasticity is not the main functional limitation for movement of the ankle joint during gait in children with CP. Despite relative exaggeration of reflexes during gait, unloading of the active plantar flexors produced a similar or in some cases a smaller drop in the soleus EMG activity in the children with CP compared to control children. This indicates that sensory feedback mechanisms contribute less to the soleus EMG activity in children with CP than in control children. We thus argue that exaggeration of reflex activity is unlikely to contribute to foot drop and toe walking in the children with CP.
Antispastic treatment is therefore unlikely to benefit the children functionally and we argue that therapy and treatment strategies should rather be directed at passive muscle changes.

Study III was performed in order to explore whether intensive gait training on a treadmill with incline could reduce passive muscle stiffness in the ankle joint and maybe facilitate a more appropriate heel strike in children with CP. The study demonstrated that children with increased passive stiffness prior to intervention significantly reduced passive stiffness following training. This indicates that it is possible to reverse the development of passive muscle stiffness and maybe even prevent the development of contractures if the problem is revealed sufficiently early.

These three studies together highlight the essence of proper clinical evaluation in order to ensure the most optimal treatment and intervention for the individual child. Interventions involving physical activity and specific training may be more appropriate solutions than antispastic therapy for many of the children.