No abstract

SUMMARY Segmental kinematics were investigated in horses during overground locomotion and compared with published reports on humans and other primates to determine the impact of a large neck on rotational mobility (>20 deg.) and stability (≤20 deg.) of the head and trunk. Three adult horses (Equus caballus) performing walks, trots and canters were videotaped in lateral view. Data analysis included locomotor velocity, segmental positions, pitch and linear displacements and velocities, and head displacement frequencies. Equine, human and monkey skulls and cervical spines were measured to estimate eye and vestibular arc length during head pitch displacements. Horses stabilized all three segments in all planes during all three gaits, unlike monkeys and humans who make large head pitch and yaw rotations during walks,and monkeys that make large trunk pitch rotations during gallops. Equine head angular displacements and velocities, with some exceptions during walks, were smaller than in humans and other primates. Nevertheless, owing to greater off-axis distances, orbital and vestibular arc lengths remained larger in horses, with the exception of head–neck axial pitch during trots, in which equine arc lengths were smaller than in running humans. Unlike monkeys and humans, equine head peak-frequency ranges fell within the estimated range in which inertia has a compensatory stabilizing effect. This inertial effect was typically over-ridden, however, by muscular or ligamentous intervention. Thus, equine head pitch was not consistently compensatory, as reported in humans. The equine neck isolated the head from the trunk enabling both segments to provide a spatial reference frame.

Trained ballet dancers and nondancer controls completed six balance tests using computerized dynamic posturography. The tests facilitated assessment of the type of sensory organization used to maintain postural control under conditions ranging from quiet standing to a situation in which visual and/or somatosensory information was systematically removed or made unreliable. Results indicated that ballet dancers and controls have comparable balance ability during eyes open and eyes closed conditions. However, when somatosensory information alone or in combination with visual information was made unreliable, dancers were significantly less stable than controls and utilized a hip strategy to maintain postural control.

Prenatal exposure to alcohol is known to affect gross motor functioning. Animal studies have shown that balance is particularly affected, and there is some evidence that similar deficits exist in alcohol-exposed children. In the current study, postural balance, or the ability to maintain equilibrium, was assessed in a group of alcohol-exposed children (ALC group; n = 11) and controls (NC group; n = 11) individually matched for age and sex. Balance was measured across six conditions designed to systematically manipulate or eliminate visual or somatosensory information. Equilibrium and strategy scores for each condition and a derived composite balance score were analyzed. Although the ALC group had a lower mean composite balance score, their performance was similar to that of the NC group on all conditions where somatosensory input was reliable. However, when somatosensory input was manipulated, and when both somatosensory and visual input were inaccurate, the ALC group performed more poorly than controls. Interestingly, there were no differences between the ALC group and NC group in the type of control strategy used to maintain balance. These results suggest that alcohol-exposed children are overly reliant on somatosensory input. When this input is atypical, alcohol-exposed children display significantly greater anterior-posterior body sway and are unable to compensate using available visual or vestibular information. These deficits may be related to cerebellar anomalies previously reported in fetal alcohol syndrome children.