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DECLINES IN FUNCTIONAL POSTURAL COMPONENTS CONTRIBUTE TO INSTABILITY AND FALLS WITH AGING FIG. 8. Schematic representation of the effects of disordered functional components of postural control on the incidence of falls in the elderly. The central plot [adapted from (72)] shows the incidence of falls as a function of age in the general population. The generalized tendency to fall actually reflects the complex summation of pathology and age-related declines in many different components of postural control which may be unique for each individual.

Figure 8 DECLINES IN FUNCTIONAL POSTURAL COMPONENTS CONTRIBUTE TO INSTABILITY AND FALLS WITH AGING FIG. 8. Schematic representation of the effects of disordered functional components of postural control on the incidence of falls in the elderly. The central plot [adapted from (72)] shows the incidence of falls as a function of age in the general population. The generalized tendency to fall actually reflects the complex summation of pathology and age-related declines in many different components of postural control which may be unique for each individual.

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FIG. 1. Schematic representations of two models of the effect of age-related changes in neural function on postural stability. (A) Neural function (solid line) declines as a function of age only. Shaded area shows the degree of decline necessary to produce observable postural instability. The heterogeneity of postural control in the elderly population is shown by the dotted lines, which show increasing levels of variability in neural function with increasing age. (B) The effect of age alone on neural function is represented by the solid line. The effect of any given pathology or pathologies is represented by the dotted lines. While the effect of age and either pathology alone is not sufficient to result in observable postural instability, the combined effect of all factors produces disequilibrium.
FIG. 1. Schematic representations of two models of the effect of age-related changes in neural function on postural stability. (A) Neural function (solid line) declines as a function of age only. Shaded area shows the degree of decline necessary to produce observable postural instability. The heterogeneity of postural control in the elderly population is shown by the dotted lines, which show increasing levels of variability in neural function with increasing age. (B) The effect of age alone on neural function is represented by the solid line. The effect of any given pathology or pathologies is represented by the dotted lines. While the effect of age and either pathology alone is not sufficient to result in observable postural instability, the combined effect of all factors produces disequilibrium.
FIG. 2. Examples of generalized measures of increasing postural instabil- ity with age. (A) Ratio of sway energy with eyes closed to sway energy with eyes open as a function of age. Subjects stood on a fixed force platform and sway energy was estimated by integrating the power spectrum of anterior/posterior displacement of the center of pressure in millimeters over a 15-second trial [adapted from (10)]. (B) Estimated sway area as a function of age for stance with eyes open and eyes closed [adapted from (108)]. Subjects stood on a fixed surface and wore a harness bearing a stylus which traced the sway path on grid paper (10 squares to the inch). The vertical axis shows the number of squares entered by the sway path on each trial averaged across subjects. Both figures show sway with eyes closed increasing with age more quickly than sway with eyes open.
FIG. 2. Examples of generalized measures of increasing postural instabil- ity with age. (A) Ratio of sway energy with eyes closed to sway energy with eyes open as a function of age. Subjects stood on a fixed force platform and sway energy was estimated by integrating the power spectrum of anterior/posterior displacement of the center of pressure in millimeters over a 15-second trial [adapted from (10)]. (B) Estimated sway area as a function of age for stance with eyes open and eyes closed [adapted from (108)]. Subjects stood on a fixed surface and wore a harness bearing a stylus which traced the sway path on grid paper (10 squares to the inch). The vertical axis shows the number of squares entered by the sway path on each trial averaged across subjects. Both figures show sway with eyes closed increasing with age more quickly than sway with eyes open.
FUNCTIONAL COMPONENTS OF POSTURAL CONTROL The list of proposed functional components of postural control in Table 1 is not exhaustive. Rather, it gives the more important components of the postural response which have been identified in recent studies of basic postural contro! mechanisms. Also, the functional components are arbi- trarily divided into motor and sensory categories, although it is clear that the sensory and motor components are closely related. For example. disequilibrium could result from pathology either in the traditional ‘*sen- sory’ or *‘motor’’ nervous systems. Further, a sensory disorder is likely to have an impact on a motor component and vice versa. TABLE |
FUNCTIONAL COMPONENTS OF POSTURAL CONTROL The list of proposed functional components of postural control in Table 1 is not exhaustive. Rather, it gives the more important components of the postural response which have been identified in recent studies of basic postural contro! mechanisms. Also, the functional components are arbi- trarily divided into motor and sensory categories, although it is clear that the sensory and motor components are closely related. For example. disequilibrium could result from pathology either in the traditional ‘*sen- sory’ or *‘motor’’ nervous systems. Further, a sensory disorder is likely to have an impact on a motor component and vice versa. TABLE |
FIG. 3. Illustration of the three most commonly used movement strategies for correcting anterior/posterior sway: (left) ankle strategy, (middle): hip strategy. and (right): stepping strategy. Left shows an ankle strategy in a healthy elderly man asked to sway forward to his limits of stability. Middle shows a hip strategy in a posturally unstable woman asked to sway forward to her stability limits. When asked to sway backwards (right), this subject used a stepping strategy.
FIG. 3. Illustration of the three most commonly used movement strategies for correcting anterior/posterior sway: (left) ankle strategy, (middle): hip strategy. and (right): stepping strategy. Left shows an ankle strategy in a healthy elderly man asked to sway forward to his limits of stability. Middle shows a hip strategy in a posturally unstable woman asked to sway forward to her stability limits. When asked to sway backwards (right), this subject used a stepping strategy.
FIG. 4. Schematic representations of normal (A, B, and C) and abnormal (D and E) postural muscle activation patterns in response to backward surface translations, which cause forward body displacement. Burst activation in representative muscle antagonists around the ankle (gastrocnemius and tibialis anterior), knee (hamstrings, biceps femoris and quadriceps, rectus femoris), and hip (rectus abdominis and lumbar paraspinals) are drawn as triangles with the dorsal muscles of the ankle strategy as solid symbols and the ventral muscles of the hip strategy as open symbols. [Adapted from (47), (49), and (87).] Thick arrows show direction of motion of body segments resulting from activation of muscle pattern.
FIG. 4. Schematic representations of normal (A, B, and C) and abnormal (D and E) postural muscle activation patterns in response to backward surface translations, which cause forward body displacement. Burst activation in representative muscle antagonists around the ankle (gastrocnemius and tibialis anterior), knee (hamstrings, biceps femoris and quadriceps, rectus femoris), and hip (rectus abdominis and lumbar paraspinals) are drawn as triangles with the dorsal muscles of the ankle strategy as solid symbols and the ventral muscles of the hip strategy as open symbols. [Adapted from (47), (49), and (87).] Thick arrows show direction of motion of body segments resulting from activation of muscle pattern.
FIG. 5. (A) Summary of experimental protocol used to test the ability of subjects to rapidly and accurately select a reliable source of sensory information for postural control. Blindfolds on stick figures indicate eyes closed conditions. Boxes at the feet or the head indicate that the support surface or the visual surround were moved in proportion to the subject's sway. (B) Shows the mean peak-to-peak anterior/posterior sway in each sensory condition for a group of young adults (open bars),.a group of elderly adults with no history of falls (‘‘asymptomatic elderly,’’ solid bars), and a group of elderly adults complaining of dizziness and imbalance (‘‘symptomatic elderly,’’ shaded bars). Data shown are for subjects who did not fall during the test. (C) Percentage of subjects who fell in each condition in each group.
FIG. 5. (A) Summary of experimental protocol used to test the ability of subjects to rapidly and accurately select a reliable source of sensory information for postural control. Blindfolds on stick figures indicate eyes closed conditions. Boxes at the feet or the head indicate that the support surface or the visual surround were moved in proportion to the subject's sway. (B) Shows the mean peak-to-peak anterior/posterior sway in each sensory condition for a group of young adults (open bars),.a group of elderly adults with no history of falls (‘‘asymptomatic elderly,’’ solid bars), and a group of elderly adults complaining of dizziness and imbalance (‘‘symptomatic elderly,’’ shaded bars). Data shown are for subjects who did not fall during the test. (C) Percentage of subjects who fell in each condition in each group.
FIG. 7. Comparison of the maximum forward and backward center of gravity positions for an elderly (A) and a young (C) subject asked to voluntarily lean to the limits of their stability. B and D show the center of gravity position for a 20-second trial of stance on a sway-referenced platform with eyes open for the same subjects. Notice how much further the elderly subject can actually control her center of gravity (CG) in B than she perceives in A.
FIG. 7. Comparison of the maximum forward and backward center of gravity positions for an elderly (A) and a young (C) subject asked to voluntarily lean to the limits of their stability. B and D show the center of gravity position for a 20-second trial of stance on a sway-referenced platform with eyes open for the same subjects. Notice how much further the elderly subject can actually control her center of gravity (CG) in B than she perceives in A.
Related topics:
AgingPostural BalanceNeurobiology of AgingNervous System DiseasesBiomechanical Phenomena
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