demonstrated that maximum amplitude of head rotations in the pitch and roll planes starts
improving during the first weeks of autonomous ambulation and attains mean values close
to the mature range within 6–32 weeks (Ledebt and Bril 2000).
A cross-sectional study of walking in typically developing children, in which
children were studied in conditions with minimal equilibrium demands (overground
walking) and in difficult balance conditions (narrow beam walking), has shown that adoption
of head stabilisation in space is confined to easy locomotor tasks in 3- to 6-year-old children,
to be subsequently extended to difficult tasks in 7- to 8-year-olds (Assaiante and Amblard
1993). In typically developing children aged 7–8 years, dynamic control of head
displacement in the pitch and yaw planes attains near-adult features, whereas less effective
performance occurs in the roll plane (Assaiante and Amblard 1993). This indicates that
acquisition of the ability to ‘anchor’ the head position to gravity-linked reference frames
over a functionally effective spectrum of locomotor tasks runs a protracted developmental
course.
In addition to the above basic head stabilisation actions, minor patterns of head (and
trunk) motion in the sagittal plane were described during ambulation. These consist of lowamplitude
forward and downward head pitches, which are thought to compensate for vertical
trunk translations, both by minimising peak accelerations at the head and by assisting visual
fixation, when needed (Mulavara and Bloomberg 2002). Compared with the strategy of
head stabilisation in space, such a fine coordination strategy has a slower developmental
evolution, in that, by the end of the first year of independent walking, it has attained about
50% of the adult performance level (Ledebt and Wiener-Vacher 1996).
Quantitative evaluation of head stability during treadmill walking in 7- to 12-year-old
children with bilateral or mild unilateral spastic CP was performed by Holt et al. (1999), who
adopted a variability measure of the vertical displacement of the head. The study revealed
that the variability of fluctuations in the amplitude of head displacement of children with
CP only differed to a minor extent from that of typically developing children. At variance,
the variability of fluctuation in the period of head displacement was significantly higher than
that of the controls. This finding suggests that in children with CP timing rather than spatial
control of head position during walking might be mainly impaired. Further studies are
necessary for ascertaining the suboptimal ability to control dynamic head rotation in the
three planes during ordinary overground walking in the different forms of CP. Such studies
are needed in particular because it is known that children with CP, examined in a sitting
position, may show significant disturbances of head–eye coordination and gaze stabilisation,
which might yield possible effects on the processing of vestibular and/or visual information
(van der Weel et al. 1996). Similar dysfunctions might also interfere with gait performance.