CONSTRAINTS ON DISORDERED LOCOMOTION - A DYNAMICAL-SYSTEMS PERSPECTIVE ON SPASTIC CEREBRAL-PALSY

Upper motor neuron disorders (UMN) result in abnormal movement pattern s that are due to spasticity, weakness, cocontraction of muscles, inap propriate timing of muscle activations in relation to maximal mechanic al advantage, and changes in the mechanical properties of muscles and connective tissues, Since many of the patterns observed in gait are re miniscent of immature patterns in non-disabled toddlers, prolonged abn ormal patterns are often viewed as a failure of normal neural maturati on. Since the 1960's the emphasis of therapeutic interventions has bee n to 'normalize' the movement pattern through a variety of neurotherap eutic techniques. The efforts have met with limited success. Recently there have been a number of publications that have emphasized the poss ibility that the observed patterns may develop or be functional adapta tions to a neural system that is not 'normal', and that the observed m ovement patterns in pathological populations may be normal and optimal for that system (Fetters, 1991; Holt, 1993; Latash and Anson, in pres s; Winter et al., 1990). Some authors have emphasized that alternative patterns develop and are facilitated by redundancy in the motor syste m (Latash and Anson, in press). Our emphasis has been to pursue the no tion that pattern development and functional adaptations in locomotion are driven by the underlying dynamics of the task and the dynamic res ources available to the individual. We use a model developed within th e dynamical systems framework, the force-driven, pendulum-spring model of locomotion, to parse out the energy forms that are needed for cont inued oscillations, and relate the energy forms to the dynamics that a re available to a disordered system, specifically, spastic cerebral pa lsy (CP). We then attempt to relate the available dynamics to the obse rved gait patterns. In this way. we seek to understand ordered and dis ordered gaits as alternative functional solutions to the dynamical req uirements for continued cycling of a periodically forced oscillator. T he implications of the theoretical model and experimental findings are discussed with respect to therapeutic intervention, and the dynamical systems approach.