Undisturbed upright stance control in the elderly: Part 1. Age-related changes in undisturbed upright stance control

The authors investigated age-related changes in postural control in 33 healthy young adults (18-31 years), 29 seniors (62-75 years), and 22 elderly people (75-96 years). A force platform recorded the results. The horizontal motions of the center of gravity (CGh) and their difference in the plane of support CP - CGv were deduced from the complex center of pressure (CP) trajectories. With fractional Brownian modeling, one can establish that the aging process seems to induce a transition phase in which seniors take more time to initiate the corrective process in the mediolateral (ML) axis than do younger people. The elderly develop a new strategy characterized by the mobilization of higher neuromuscular energy to maintain equilibrium. In the ML axis, the larger displacements could be caused mainly by a hip strategy that could facilitate step initiation. In the anteroposterior (AP) axis, seniors and elderly individuals maintain a relative ability to stabilize their CG into the base of support compared with younger people.     

Undisturbed Upright Stance Control in the Elderly: Part 1. Age-Related Changes in Undisturbed Upright Stance Control

The authors investigated age-related changes in postural control in 33 healthy young adults (18-31 years), 29 seniors (62-75 years), and 22 elderly people (75-96 years). A force platform recorded the results. The horizontal motions of the center of gravity (CG_h) and their difference in the plane of support CP - CG_v were deduced from the complex center of pressure (CP) trajectories. With fractional Brownian modeling, one can establish that the aging process seems to induce a transition phase in which seniors take more time to initiate the corrective process in the mediolateral (ML) axis than do younger people. The elderly develop a new strategy characterized by the mobilization of higher neuromuscular energy to maintain equilibrium. In the ML axis, the larger displacements could be caused mainly by a hip strategy that could facilitate step initiation. In the anteroposterior (AP) axis, seniors and elderly individuals maintain a relative ability to stabilize their CG into the base of support compared with younger people.     

Undisturbed Upright Stance Control in the Elderly: Part 2. Postural-Control Impairments of Elderly Fallers

A common way of predicting falling risks in elderly people can be to study center of pressure (CP) trajectories during undisturbed upright stance maintenance. By estimating the difference between CP and center of gravity (CG) motions (CP - CG_v), one can estimate the neuromuscular activity. The results of this study, which included 34 sedentary elderly persons aged over 75 years (21 fallers and 13 nonfallers), demonstrated significantly increased CG_h and CP - CG_v motions in both axes for the fallers. In addition, the fallers presented larger CG_h motions in the mediolateral axis, suggesting an enlarged loading—unloading mechanism, which could have reflected the adoption of a step-initiating strategy. As highlighted by fractional Brownian motion modeling, the distance covered by the CP - CG_v motions before the successive control mechanisms switched was enhanced for the fallers in both axes, therefore increasing the risk that the CG would be outside of the base of support.     

Effects of breathing on multijoint control of center of mass position during upright stance

ABSTRACT Breathing exerts destabilizing effects on postural stability during quiet stance. The authors conducted an experiment to evaluate the role of motor abundance in the organization of the postural synergy compensating for the effects of breathing. They measured the kinematic pattern of covariation among the major joints of the postural chain (ankle, knee, hip, trunk, and neck) as a function of different breathing modes (spontaneous, paced, and increased volume) and different stance instructions (still vs. relaxed) using the uncontrolled manifold approach. Joint variability was structured to preserve the stable position of the center of mass. This result supports the hypothesis that motor abundance of the postural chain plays an important role in the flexible compensation for breathing during quiet stance.     

Lower limb muscle fatigability is not associated with changes in movement strategies for balance control in the upright stance

BackgroundFatigue is a distressing symptom inversely related to postural stability in adults with neuromuscular and systemic diseases. However, there is no information about the effects of lower limb muscles fatigability on the movement strategies for balance control in the upright standing.MethodsThis study enrolled 41 healthy subjects (female/male: 22/19; age 23 ± 3 years; body mass index 25.4 ± 3.7 kg/m²). Participants underwent posturography and surface electromyography of the gastrocnemius medialis muscle during a sustained, fatiguing voluntary contraction of the gastrocnemius preceded and followed by quiet standing (120 s). Amplitude of electromyograms and fatigability were evaluated using the root mean square (RMS) value and both the RMS and spectral median frequency (f_med) slopes. Balance control was evaluated using the center-of-pressure elliptic area (Area) and average velocity (Vavg). Movement strategies for balance control were evaluated using the number of high-density regions (nHDR) and spatial patterns of the three-dimensional statokinesigram.ResultsMean time to muscle fatigability was 258 ± 190 s. Area and Vavg but not nHDR increased after the fatiguing task. Single-centered spatial patterns were predominant in both tasks (pre-fatigue: n = 22/41; post-fatigue: n = 19/41), with no evidence of an association between the spatial patterns and tasks (γ = 0.237, 95%CI = [−0.338; 0.542]).ConclusionsLower limb muscle fatigability increases postural instability, but it is not associated with changes in movement strategies for balance control in the upright stance.     

Accuracy of weightbearing at three target levels during bilateral upright stance in patients with neuropathic feet and control subjects

The purposes of this study were to (1) describe errors in weightbearing at three target levels for patients with neuropathic feet and control subjects, (2) compare the absolute errors at the three target levels between groups, and (3) identify predictor variables of errors in weightbearing by the neuropathic group. The groups of 26 subjects were matched for age and height. Weightbearing was measured with digital scales while subjects attempted to adjust their weight through a designated lower extremity to each target level (25, 50, and 75% of body weight). Analysis of variance indicated no significant difference in the percentage weightbearing between groups at the three target levels. There was a significant difference in errors made in weightbearing by the groups at the three target levels. Mean errors ranged from 8.5 to 9.7% for the neuropathic group and from 2.4 to 6.6% for the control group. The findings cast doubt on the utility (in the absence of feedback) of requesting individuals, particularly those with neuropathic feet, to weightbear at specific target levels.     

Center of gravity motions and ankle joint stiffness control in upright undisturbed stance modeled through a fractional Brownian motion framework

The authors modeled the center of gravity vertical projection (CG(v)) and the difference, CP - CG(v), which, combined, constitute the center of pressure (CP) trajectory, as fractional Brownian motion in order to investigate their relative contributions and their spatiotemporal articulation. The results demonstrated that CG(v) and CP - CG(v) motions are both endowed in complementary fashion with strong stochastic and part-deterministic behaviors. In addition, if the temporal coordinates remain similar for all 3 trajectories by definition, the switch between the successive control mechanisms appears for shorter displacements for CP - CG(v) and CG(v) than for CP trajectories. Results deduced from both input (CG(v)) and muscular stiffness (CP - CG(v)) thus provide insight into the way the central nervous system regulates stance control and in particular how CG and CP - CG are controlled.     

Affordances as constraints on the control of stance

In this article we present an ecological treatment of the control of stance by multi-segment organisms. We treat the organism as a black box, and the organism-environment interaction as a closed-loop system. We argue that different ways of controlling stance can have differing utility (affordances) for perception and action. We further argue that the affordances of a particular control strategy are in part determined by (a) the mechanical properties of the organism, (b) the mechanical properties of the surface on which stance takes place, and (c) the goals of behavior. Our conclusion is that the control of stance is based on, or constrained by, perception of the kinematic consequences, or affordances, of control actions. Finally, we argue that the relationship between affordances and constraints on control actions should be investigated using geometrical methods.     

Analysis of the transition from upright stance to steady state locomotion in children with under 200 days of autonomous walking

The aim of this paper was to study, from a developmental perspective, the transient phase of gait during the period between the standing posture and the achievement of steady state gait, using temporal and biochemical parameters. Eight children who had been walking autonomously for 90 to 200 days were observed. A total of 64 sequences of steps were analyzed. A sequence of steps began with the child standing still and was executed on a large force plate. From the determination of the instantaneous velocity of center of gravity results establish that, unlike adults, progression velocity in children end of the first step, but after two to four steps.The gait initiation process does not depend on the steady state velocity, but results from an initial fall. The duration of the movement up to the end of the first step is independent of the progression velocity but depends only upon the body mass and moment of inertia of the children.     

Flow structure versus retinal location in the optical control of stance

In four experiments I examined the importance of the retinal center and periphery in the pickup of optical information for controlling stance as a function of the dynamic geometrical structure of the optical flow. All experiments were performed in a moving room so that the magnitude of compensatory sway in response to room movements could be measured. In Experiments 1 and 2 I found stronger sway response to flow having a largely lamellar structure that was presented to the retinal periphery than to more radially structured flow in the center. In Experiment 3 observers turned their heads to face the right wall of the room, placing radial flow in the periphery and lamellar flow in the center of the visual field. Radial flow presented to the retinal periphery induced no compensatory sway. Lamellar flow in the center of the retina produced some sway. Flow structure apparently interacts with the exposed retinal area in controlling stance.     

Prediction of locus of control stance from the earliest childhood memory

The study was designed to test whether data from the earliest childhood memory (EM) could predict a Rotter internal vs external locus of control stance. Main Study subjects were 215 undergraduates from introductory psychology classes. Those EMs which could be reliably scored and coded for control stance--153 of the 215 Main Study protocols--were examined for success at predicting Rotter control stance. A total of 127 of 153 control predictions were correct, which yielded a Chi Square of 67.51, p < .0005 for a 2 x 2 table. Further, all 5 EM content hypotheses, which were based on groupings of the 54 Pilot Study codes, yielded results significant at p < .05. These results were discussed as supporting the validity of EMs to predict control stance and as contributing to an understanding of the dynamic basis for and maintenance of a belief in internal vs external control.     

Major depression in the transition to adulthood: risks and impairments.

An ongoing longitudinal community study (N = 375) examined childhood risks and later adult impairments associated with 1-year Diagnostic and Statistical Manual of Mental Disorders (3rd ed., rev.; American Psychiatric Association, 1987) diagnoses of major depression during the transition to adulthood. Risks from birth to age 9 were reported by mothers, participants, and teachers. Teacher-reported hostility at age 6 predicted later depression. At age 9, self-perceptions of anxiety/depression, unpopularity, familial rejection, and abuse were potent risks. For men, neonatal and childhood health problems predicted later depression. For women, risks included family constellation, parental death, and poor academic achievement at age 9. Men and women who were depressed at age 18, age 21, or both demonstrated extensive psychosocial impairments in early adulthood, including poor overall functioning, interpersonal and behavioral problems, low self-esteem, and suicidality.     

Visuographic tests of set shifting and inhibitory control. The contribution of constructional impairments

Luria's graphical or alternating sequences test (the ‘rampart’ design) is a well‐known procedure to examine attentional processes such as set shifting and inhibition of competing responses. Although the test requires attentional control over inappropriate responses, it also relies on constructional abilities that may hamper the specificity of the test. In order to control for the influence of constructional abilities, the structural equation modelling (path analysis) was used to examine the correlations between the performance on alternating sequences and an independent criterion measure of executive functioning (the Behavioural Dyscontrol Scale), corrected for the influence of visuoconstructional ability as reflected by performance on a task of design copying. The tests were administered to 950 elderly participants in a psychogeriatric day‐care programme. Performance on the Behavioural Dyscontrol Scale (BDS) and the copying tasks jointly predicted performance on the alternating sequences test (AST) (multiple R²=.41). Though the effect of BDS on AST was 38.9% mediated by constructional ability, BDS scores predicted performance on graphical sequences above and beyond the influence of drawing ability. In a non‐parametric classification tree analysis, the performance on the AST was reliably predicted by drawing ability. When BDS performance was added to the analysis, the classification accuracy increased for participants with poor drawing, but remained unchanged for those who performed in the normal range on the copying tasks. As a task that relies on shifting and inhibitory control, the alternating sequences test is a feasible measure of executive functioning that is relatively independent of the influence of the component drawing skills.     

Health stresses and depressive symptomatology in the elderly: the importance of health engagement control strategies.

The study presents cross-sectional (N = 127) and longitudinal (n = 111) analyses examining relations between health engagement control strategies (HECSs), depressive symptoms, and health stresses in elderly individuals. HECS was measured as people's behavioral and cognitive investments toward attaining health goals. HECS was related to low levels of depressive symptoms, particularly among people experiencing acute physical symptoms. Moreover, HECS predicted reduction of depressive symptoms over time, and depressive symptomatology predicted negative change in HECS. The findings show that active investments of HECSs significantly moderate the negative affective consequences of health threats. Individuals who are characterized by low levels of HECS and high levels of depressive symptoms may be at increased risk of accelerated decline in their physical and mental health.     

Sensori-motor integration during stance: Time adaptation of control mechanisms on adding or removing vision

Sudden addition or removal of visual information can be particularly critical to balance control. The promptness of adaptation of stance control mechanisms is quantified by the latency at which body oscillation and postural muscle activity vary after a shift in visual condition. In the present study, volunteers stood on a force platform with feet parallel or in tandem. Shifts in visual condition were produced by electronic spectacles. Ground reaction force (center of foot pressure, CoP) and EMG of leg postural muscles were acquired, and latency of CoP and EMG changes estimated by t-tests on the averaged traces. Time-to-reach steady-state was estimated by means of an exponential model. On allowing or occluding vision, decrements and increments in CoP position and oscillation occurred within about 2 s. These were preceded by changes in muscle activity, regardless of visual-shift direction, foot position or front or rear leg in tandem. These time intervals were longer than simple reaction-time responses. The time course of recovery to steady-state was about 3 s, shorter for oscillation than position. The capacity of modifying balance control at very short intervals both during quiet standing and under more critical balance conditions speaks in favor of a necessary coupling between vision, postural reference, and postural muscle activity, and of the swiftness of this sensory reweighing process.     

Forgoing life-sustaining treatment: limits to the consensus. Part 2

While substantial progress has been made in reaching a moral and policy consensus regarding forgoing life-sustaining treatment, several holes exist in that consensus where more public discussion and moral analysis is needed. First, among patients who have not been found to be legally incompetent there is controversy over whether certain treatments can be refused. Controversies also remain over damages for treatment without consent, limits based on third-party interests and the ethical integrity of the medical profession, and cases where it cannot be agreed whether the patient is competent. Even greater dispute exists over care of incompetent patients. Perhaps the greatest gap in the consensus arises over limits to the use of the best interests standard. This article proposes replacing it with a "reasonableness standard" that takes into account disputes about what is literally the best for the patient and conflicts of interest between the patient and others.     

Posture control and complex arm coordination: analysis of multijoint coordinative movements and stability of stance

The authors addressed the interactions between control of bimanual multijoint coordination tasks and posture. Participants (N = 6) performed 8 coordination patterns that differed in degree of complexity by using their bilateral elbows and wrists under 3 scaled motion speeds while standing on 2 force plates. Results indicated that producing complex bimanual multijoint coordinative tasks affected postural sway, thus resulting in an increase of sway activity. Behavioral as well as mechanical factors accounted for the increased disturbance in postural sway. Those findings suggest that performing complex coordination tasks disrupts postural control in normal young adults.