  Summary: Walking is regulated through the motorcontrol system (MCS). The MCS
consists of a network of neurons from the central nervous system (CNS) and the
intraspinal nervous system (INS), which is capable of producing a syncopated
output. The coupling of the latter two systems produces a complex stride
interval time series that is characterized by fractal and multifractal
properties that depend upon several biological and stress constraints. It has
been shown that: (i) the gait phenomenon is essentially a rhythmic cycle that
obeys particular phase symmetries in the synchronized movement of the limbs;
(ii) the fractal and multifractal nature of the stride interval fluctuations
become slightly more pronounced under faster or slower paced frequencies
relative to the normal paced frequency of a subject; (iii) the randomness of
the fluctuations increases if subjects are asked to synchronize their gait with
the frequency of a metronome or if the subjects are elderly or suffering from
neurodegenerative disease. Here we present a new model, called the super
central pattern generator, able to reproduce these known properties of walking
and discuss the physiological and psychological interpretations of the model
parameters.
