Abstract
BackgroundThe control of the head movements during walking allows for the stabilisation of the optic flow, for a more effective processing of the vestibular system signals, and for the consequent control of equilibrium.In young individuals, the oscillations of the upper body during level walking are characterised by an attenuation of the linear acceleration going from pelvis to head level. In elderly subjects the ability to implement this motor strategy is reduced. The aim of this paper is to go deeper into the mechanisms through which the head accelerations are controlled during level walking, in both young and elderly women specifically.MethodsA stereophotogrammetric system was used to reconstruct the displacement of markers located at head, shoulder, and pelvis level while 16 young (age: 24 ± 4 years) and 20 older (age: 72 ± 4 years) female volunteers walked at comfortable and fast speed along a linear pathway. The harmonic coefficients of the displacements in the medio-lateral (ML), antero-posterior (AP), and vertical (V) directions were calculated via discrete Fourier transform, and relevant accelerations were computed by analytical double differentiation. The root mean square of the accelerations were used to define three coefficients for quantifying the attenuations of the accelerations from pelvis to head, from pelvis to shoulder, and from shoulder to head.ResultsThe coefficients of attenuation were shown to be independent from the walking speed, and hence suitable for group and subject comparison.The acceleration in the AP direction was attenuated by the two groups both from pelvis to shoulder and from shoulder to head. The reduction of the shoulder to head acceleration, however, was less effective in older women, suggesting that the ability to exploit the cervical hinge to attenuate the AP acceleration is challenged in this population. Young women managed to exploit a pelvis to shoulder attenuation strategy also in the ML direction, whereas in the elderly group the head acceleration was even larger than the pelvis acceleration.ConclusionThe control of the head acceleration is fundamental when implementing a locomotor strategy and its loss could be one of the causes for walking instability in elderly women.
Highlights
The oscillations of head, trunk and pelvis during level walking are the result of a compass gait [1]
If seen by an observer moving at the mean velocity of progression, they are characterised by quasi sinusoidal trajectories which, as such, allow for minimal accelerations and, for the stabilisation of the optic flow, for a more effective processing of the vestibular system signals, and for the consequent control of equilibrium [2,3,4]
The walking speed reached by the YG in the fast speed (FS) trials was significantly higher than that of the EG, but still below the threshold
Summary
The oscillations of head, trunk and pelvis during level walking are the result of a compass gait [1]. In able-bodied individuals, both the lumbar and the cervical hinges play an important role in determining the attenuation of the mechanical perturbations transmitted from the hips, through the pelvis and the spinal column up to the head This attenuation manifests itself in the fact that the resultant acceleration tends to decrease going from pelvis to head level [5,6,7]. This is mostly due to a decrease of the antero-posterior (AP) acceleration component, as seen through its root mean square (RMS) value. The aim of this paper is to go deeper into the mechanisms through which the head accelerations are controlled during level walking, in both young and elderly women
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