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PubMed1987

Effects of posture and ageing on circulating atrial natriuretic peptide levels in man.

Possible influences of posture or age on plasma immunoreactive atrial natriuretic peptide (irANP) levels and potential correlates were assessed in 12 young (age +/- s.e.m. 24 +/- 1 year) and 12 elderly (63 +/- 8 year) healthy subjects on a liberal sodium intake. The groups did not differ significantly in their basal 24-h urinary sodium excretion (210 +/- 23 versus 180 +/- 15 mmol/l). However, plasma irANP was five- to ninefold higher in the elderly (P less than 0.05-0.01). Plasma irANP averaged 167 +/- 31 and 24 +/- 3 pg/ml in the elderly and young, respectively, during recumbency, fell (P less than 0.05) to 101 +/- 21 and 11 +/- 1 pg/ml, respectively, with upright posture, and rose (P less than 0.01) to 250 +/- 51 and 50 +/- 9 pg/ml, respectively, after intravenous (i.v.) loading with 0.9% saline (2.14 l in 3 h). Supine blood pressure (BP) and plasma norepinephrine tended to be higher while renin and aldosterone levels were lower (P less than 0.01) in the elderly; the three latter variables rose (P less than 0.001) with upright posture. These findings demonstrate that in normal humans, circulating irANP levels vary with posture and ageing. These changes may have potential physiological relevance and should be considered when interpreting plasma irANP levels in pathological conditions.

Adult↗
PubMed2004

Haemodynamic responses to physical activity and body posture during everyday life.

OBJECTIVE: To determine the relationships between body posture and physical activity and systemic haemodynamics during everyday life. METHODS: Continuous measurements were performed in 34 subjects (16 hypertensive, 12 male), aged 49 +/- 13 (mean +/- standard deviation) years. Blood pressure (BP) was measured in the brachial artery. Physical activity and posture were measured with four accelerometers. Beat-to-beat values of systolic blood pressure (SBP), diastolic blood pressure (DBP), heart rate (HR), stroke volume (SV), cardiac output (CO) and systemic vascular resistance (SVR) were computed from the pressure waveforms. Multiple correlation coefficients (R) between activity and haemodynamic variables were computed and responses to physical activity were estimated with random regression models. RESULTS: The overall percentages of variance in SBP, DBP, HR, SV, CO and SVR explained by activity (R2) were 32, 28, 56, 44, 74, and 45%, respectively. The SBP and HR increased linearly with increasing levels of activity (19 mmHg and 30 beats/min when activity increased 90 percentiles). Other variables showed parabolic relationships. The initial decrease in SV and CO (14 ml and 0.5 l/min) and increase in DBP and SVR (9 mmHg and 2 mmHg min/l) with increasing levels of activity coincided with changes in posture (lying-sitting-standing). The subsequent SV and CO increase (23 ml and 3.7 l/min) and DBP and SVR decrease (8 mmHg and 8 mmHg min/l) coincided with changes in activity (standing-moving generally-walking). CONCLUSIONS: Our findings show that normal daily posture and activity are only moderate determinants of BP, but main determinants of HR and CO variation.

Adult↗
PubMed1995

Pulmonary function and posture in traumatic quadriplegia.

OBJECTIVE: To determine optimum posture for pulmonary function in traumatic quadriplegia. DESIGN: Lung function with changes in posture of normal healthy volunteers was compared with that of traumatic quadriplegic patients. MATERIALS AND METHODS: Functional residual capacity (FRC), Forced vital capacity (FVC), and arterial blood gases in room air were compared in 16 male patients aged 18 to 32 years, 8 of whom (group I) sustained traumatic quadriplegia (C6 to C7) at least 1 year previously, and 8 of whom (group II) were healthy volunteers. MEASUREMENTS: FRC, FVC and blood gases were measured after 15 minutes in the following random positions: 20 degrees head down, horizontal, 35 degrees head up, 60 degrees head up, and 90 degrees head up. MAIN RESULTS: FRC was lower in all positions in group I but there was a similar directional change in FRC with posture in both groups. The greatest increase in FRC occurred in group I between the 35-degree head up and the 60-degree head up positions. Group I, in contrast to group II, decreased FVC from the 35-degree head up to the 60-degree head up position. There were no significant changes in PO2 with position in group II, but quadriplegic patients showed PO2 improvement from the head down to the horizontal and 60-degree head up positions. CONCLUSIONS: In traumatic quadriplegia, maximum oxygenation and patency of alveoli (FRC) are achieved in the 60- to 90-degree head up positions. In contrast to normal subjects, no changes in FRC and FVC occurred between the horizontal and 35-degree head up positions in quadriplegia. The optimum position in these patients for physiotherapy (deep breathing and coughing, as reflected by maximum FVC) is the horizontal or 35-degree head up position. These differences in lung volumes and oxygenation with posture may be important in optimizing respiratory care in traumatic quadriplegia.

Adult↗
PubMed2002

Attentional demands and postural sway: the effect of the calf muscles fatigue.

PURPOSE: The purpose of the present experiment was to investigate whether the calf muscle fatigue affects postural sway in bipedal stance and requires additional attentional demands. METHODS: Nine healthy university students had to respond as rapidly as possible to an unpredictable auditory stimulus while maintaining stable seated and upright postures with their eyes closed in two conditions of no-fatigue and fatigue of the calf muscles. Center of foot pressure (COP) displacements were recorded using a force platform. Reaction times (RTs) values were used as an index of the attentional demand necessary for regulating postural sway. RESULTS: Fatigue yielded a significant anterior shift of mean position of the COP and increased range, mean speed, and dispersion of COP displacements. An increased attentional demand for regulating postural sway also was observed with fatigue. CONCLUSIONS: These results suggest that muscular fatigue may put the individuals at higher risk of falling, especially when engaging in concurrent tasks.

Adult↗
PubMed1994

Dark focus of accommodation and vergence posture.

We evaluated the dark focus of accommodation and vergence posture in 20 boys and girls, 10 with and 10 without accommodative esotropia, before and after they wore glasses for at least 1 month. Refractive error was measured by Nidek Autorefractometer AR1600. We used two definitions of the dark focus, DFcus (Non-Cyclo R) and DFcus (Cyclo R). DFcus (Non-Cyclo R) = Dark R - Non-Cyclo R. DFcus (Cyclo R) = Dark R - Cyclo R. (Dark R: refractive state in the dark; Non-Cyclo R: non-cycloplegic refractive error; Cyclo R: cycloplegic refractive error.) Vergence posture was measured by prism cover test during distance fixation while uncorrected. DFcus (Cyclo R) was significantly greater in esotropic subjects than in non-esotropic subjects, although DFcus (Non-Cyclo R) did not differ significantly. A significant hyperopic shift in Dark R was observed after wearing glasses. DFcus (Cyclo R) was significantly decreased after wearing glasses, suggesting that wearing glasses is an important variable of the dark focus. Unlike the dark focus, the vergence posture did not change in either group after wearing glasses. The dissociation of the dark focus from vergence posture seems to be inconsistent with previous findings. It is postulated that change in dark vergence after wearing glasses is responsible for the results.

Accommodation, Ocular↗
PubMed1986

Therapeutic effect of posture in sleep apnea.

Four patients with mild to moderate obstructive sleep apnea were monitored first in the supine posture to establish a diagnosis of obstructive sleep apnea (apnea indices 33, 12, 22, 36). A second polysomnogram, obtained while the patients slept in the lateral posture, showed a dramatic decrease in apnea (apnea indices 5, 0, 0.2, and 0) and snoring. Each patient had an enlarged uvula, which moved to the side in the lateral posture. We conclude that sleeping in the lateral posture may be therapeutic in some patients with obstructive sleep apneas.

Adult↗
PubMed1995

The effects of spinal flexion and extension exercises and their associated postures in patients with acute low back pain.

STUDY DESIGN: A prospective randomized clinical trial compared the effects of flexion and extension back exercises and postures among soldiers with acute low back pain. OBJECTIVE: To compare the immediate effects of back exercise on functional status, spinal mobility, straight leg raising, pain severity, and treatment satisfaction, and to determine whether spinal exercise during the acute stage of low back pain reduces recurrent episodes of low back pain. SUMMARY OF BACKGROUND DATA: Conflicting reports exist concerning the efficacy of spinal flexion and extension exercises in patients with low back pain of varying duration. Poor study design and lack of functional outcomes characterize many of these studies. METHODS: One-hundred-forty-nine subjects with acute low back pain received flexion exercise and posture (n = 57), extension exercise and posture (n = 62), or no exercise or posture (n = 30) for 8 weeks. Outcomes were assessed 1, 2, 4 and 8 weeks after treatment onset. A questionnaire assessed the recurrence of low back pain 6-12 months after study entry. RESULTS: Flexion and extension exercise groups did not differ in any outcome over 8 weeks. After 1 week, both exercise groups had reduced disability scores, a higher proportion returning to work, and fewer subjects with a positive straight-leg raise compared with the control group. There was no difference among groups regarding recurrence of low back pain after 6-12 months. CONCLUSIONS: There was no difference for any outcomes between the flexion or extension exercise groups. However, either exercise was slightly more effective than no exercise when patients with acute low back pain were treated.

Acute Disease↗
PubMed1996

Psychomotor speed and postural control in chronic low back pain patients A controlled follow-up study.

STUDY DESIGN: Psychomotor speed (reaction time) and postural control (center point of force velocity) among healthy control volunteers and patients with chronic low back pain (LBP) were studied at the beginning of an active, functional, restoration back rehabilitation program and 5 months after the program. OBJECTIVES: To study cross-sectionally reaction times and center points of force velocity among control volunteers and patients with low back pain, and to evaluate the effects of the restoration on these measures of motor function in a follow-up examination. SUMMARY OF BACKGROUND DATA: Deficits of motor skills and of coordination have been reported in association with musculoskeletal disorders, but one can only speculate about an association between proprioceptive dysfunction and low back disorders on the basis of the currently available data. METHODS: Sixty-one healthy control volunteers and 99 patients with low back pain-68 of these patients experienced moderate pain; 31 experienced severe pain-participated in the study. Reaction times for upper and lower limbs were tested with a system based on a microcomputer. Postural stability was measured with a vertical force platform. RESULTS: A consistent trend was found in which patients with low back pain had reaction times slower than these of control volunteers. Man with severe low back pain had significantly longer hand reaction times than men in the control group (P = 0.03). Women with severe low back pain also had poorer postural control than women with moderate low back pain (P = 0.02) and women in the control group (P = 0.04). Functional restoration seemed to have an effect on reaction times. The restoration was considered successful if the condition of a patient with a disability that had resulted from low back pain improved during the follow-up examination and unsuccessful if the disability worsened. Patients who experienced these results were identified in groups called "good" and "poor," respectively. Among men, the reaction times improved in the control group and "good" groups, but they became slower in the "poor" group. The difference between "good" and "poor" groups was significant (P = 0.008). Women in the "good" group achieved the most improved reaction times, and the difference between these women and the control women almost reached significance (P = 0.076). CONCLUSION: The results indicate that patients with chronic low back pain have impaired psychomotor speed and, among women, impaired postural control. Psychomotor speed improved during an active, functional, restoration back rehabilitation program.

Adult↗
PubMed1997

Stabilizing function of trunk flexor-extensor muscles around a neutral spine posture.

STUDY DESIGN: This study examined the coactivation of trunk flexor and extensor muscles in healthy individuals. The experimental electromyographic data and the theoretical calculations were analyzed in the context of mechanical stability of the lumbar spine. OBJECTIVES: To test a set of hypotheses pertaining to healthy individuals: 1) that the trunk flexor-extensor muscle coactivation is present around a neutral spine posture, 2) that the coactivation is increased when the subject carries a load; and 3) that the coactivation provides the needed mechanical stability to the lumbar spine. SUMMARY OF BACKGROUND DATA: Theoretically, antagonistic trunk muscle coactivation is necessary to provide mechanical stability to the human lumbar spine around its neutral posture. No experimental evidence exists, however, to support this hypothesis. METHODS: Ten individuals executed slow trunk flexion-extension tasks, while six muscles on the right side were monitored with surface electromyography: external oblique, internal oblique, rectus abdominis, multifidus, lumbar erector spinae, and thoracic erector spinae. Simple, but realistic, calculations of spine stability also were performed and compared with experimental results. RESULTS: Average antagonistic flexor-extensor muscle coactivation levels around the neutral spine posture as detected with electromyography were 1.7 +/- 0.8% of maximum voluntary contraction for no external load trials and 2.9 +/- 1.4% of maximum voluntary contraction for the trials with added 32-kg mass to the torso. The inverted pendulum model based on static moment equilibrium criteria predicted no antagonistic coactivation. The same model based on the mechanical stability criteria predicted 1.0% of maximum voluntary contraction coactivation of flexors and extensors with zero load and 3.1% of maximum voluntary contraction with a 32-kg mass. The stability model also was run with zero passive spine stiffness to simulate an injury. Under such conditions, the model predicted 3.4% and 5.5% of maximum voluntary contraction of antagonistic muscle coactivation for no extra load and the added 32 kg, respectively. CONCLUSIONS: This study demonstrated that antagonistic trunk flexor-extensor muscle coactivation was present around the neutral spine posture in healthy individuals. This coactivation increased with added mass to the torso. Using a biomechanical model, the coactivation was explained entirely on the basis of the need for the neuromuscular system to provide the mechanical stability to the lumbar spine.

Adult↗
PubMed1997

Axial rotation strength in seated neutral and prerotated postures of young adults.

STUDY DESIGN: To determine the trunk-twisting capability from neutral and prerotated postures, a study was designed to measure torque generated in isometric and isokinetic activities of 50 young adults. OBJECTIVES: To determine the isometric and isokinetic axial rotation strengths of male and female subjects in neutral and asymmetric postures and to quantify the effect of velocity of rotation on the isokinetic trunk strength profile. METHODS: A specially designed axial rotation tester was employed using specially written modular software for data collection and analysis. The isometric strengths were measured in neutral, 15 degrees, and 30 degrees prerotated trunk postures. The isokinetic strength was measured in activities starting from the neutral position to fully rotated and from a fully rotated position to neutral positions at 10 degrees, 20 degrees, and 40 degrees per second angular velocity. The data obtained were subjected to multivariate and univariate analyses of variances with multiple comparisons and multiple regression analyses. RESULTS: All study participants were significantly stronger in isometric twisting activities than in the isokinetic activities. In isometric activities, participants were 20-25% weaker in prerotated postures when twisting in the direction of prerotation and were approximately 30% stronger in the opposite direction. For isokinetic activities, the trunk rotation from neutral to asymmetric positions produced lesser torques compared with torques from rotated positions to the neutral position. The torque-producing capability declined with increasing velocity of activity. CONCLUSION: This study adds to the data base of rotational strength.

Adolescent↗
PubMed2002

Impaired lumbar movement perception in association with postural stability and motor- and somatosensory-evoked potentials in lumbar spinal stenosis.

STUDY DESIGN: A descriptive study of the associations between different neurophysiologic findings in patients with lumbar spinal stenosis. OBJECTIVES: To evaluate the ability to sense a change in lumbar position and the associations between lumbar movement perception, postural stability, and motor-evoked potentials and somatosensory-evoked potentials. SUMMARY OF BACKGROUND DATA: Patients with low back pain have impaired postural control and impaired lumbar proprioception. Altered motor-evoked potentials and somatosensory-evoked potentials have been often observed in lumbar spinal stenosis. METHODS: The study included 26 patients with clinically and radiologically diagnosed lumbar spinal stenosis. Their ability to sense lumbar rotation was assessed in a previously validated motorized trunk rotation unit in the seated position. The abilities to indicate the movement direction and the movement magnitude were used as indexes of the ability to sense the lumbar rotatory movement. The postural stability was measured with a vertical force platform. The motor-evoked potentials were elicited by transcranial and lumbar stimulation and recorded from anterior tibialis muscles. The somatosensory-evoked potentials were elicited by transcutaneous electrical stimulation of the tibial nerve at the ankle. RESULTS: Twenty patients (76.9%; P = 0.006) reported the wrong movement direction. Furthermore, the patients consistently localized the movement sensation in their shoulders instead of the lumbar region. The altered motor-evoked potentials and somatosensory-evoked potentials were observed in 11 and 16 patients, respectively. Abnormal motor-evoked potentials had inconsistent associations with impaired movement perception and postural stability and abnormal somatosensory-evoked potentials had no associations with other findings. CONCLUSIONS: Many patients with lumbar spinal stenosis have difficulties in sensing the lumbar rotational movement, which may indicate impaired proprioceptive abilities. Abnormal motor-evoked potentials and somatosensory-evoked potentials are also frequent in lumbar spinal stenosis but do not necessarily occur in the same patients as the abnormal ability to sense trunk movement. These new findings add to our understanding of the pathophysiology of lumbar spinal stenosis.

Evoked Potentials, Motor↗
PubMed2002

Historical perspective milestones in the evolution of lumbar spinal postural health in seating.

The best knowledge on seated posture before the Enlightenment was not scientific, but influenced by sociocultural, economic, and manufacturing factors. Although the pursuit of knowledge related to spinal postural health was advanced with the advent of empirico-analytic research, academic opinion continued to be influenced by unsubstantiated information, often resulting in incorrect advice to the public. Only in the past decade has advice on "correct" seated posture, spanning the time from the Hippocratic texts to the present, been brought into question by evidence-based research. By exploring seating from 3100 B.C to the present, this article discusses key influences that have an impact on seating functional to spinal postural health. Emphasis is placed on the role of medical opinion.

China↗
PubMed2002

Posture-dependent isometric trunk extension and flexion strength in normal male and female subjects.

The objective of this study was to quantify the relationship between trunk posture and trunk muscle function in a group of young, normal male and female subjects. Ten male and 10 female subjects performed isometric flexion and extension tasks using a trunk dynamometer. Peak isometric torque was recorded in flexion and extension at 10 degrees increments over a sagittal posture range of -20 degrees extension to +50 degrees of flexion. Significant differences in trunk strength (isometric torque) were found between males and females, at various sagittal plane trunk postures, and between flexion (F) and extension (E) tasks. Flexion torque was greatest at 20 degrees to 30 degrees flexion, whereas extension torque was greatest at 50 degrees flexion. Gender-specific differences in trunk strength were markedly reduced when the torque data were normalized by the subject's height multiplied by body weight. The E/F torque ratio showed a relatively linear, over twofold increase with increasing flexion angle, and was significantly greater for female subjects compared with male subjects at most sagittal postures. The baseline trunk isometric strength data provided by this study should help clinicians to use strength testing more precisely and specifically in prevention and diagnosis of patients at risk for back disorders.

Adult↗
PubMed2006

Differences in sitting postures are associated with nonspecific chronic low back pain disorders when patients are subclassified.

STUDY DESIGN: A comparative study. OBJECTIVES: To investigate sitting postures of asymptomatic individuals and nonspecific chronic low back pain (NS-CLBP) patients (pooled and subclassified) and evaluate the importance of subclassification. SUMMARY OF BACKGROUND: Currently, little evidence exists to support the hypothesis that CLBP patients sit differently from pain-free controls. Although classifying NS-CLBP patients into homogeneous subgroups has been previously emphasized, no attempts have been made to consider such groupings when examining seated posture. METHODS: Three angles (sacral tilt, lower lumbar, and upper lumbar) were measured during "usual" and "slumped" sitting in 33 NS-CLBP patients and 34 asymptomatic subjects using an electromagnetic measurement device. Before testing, NS-CLBP patients were subclassified by two blinded clinicians. Twenty patients were classified with a flexion motor control impairment and 13 with an active extension motor control impairment. RESULTS: No differences were found between control and NS-CLBP (pooled) patients during usual sitting. In contrast, analyses based on subclassification revealed that patients classified with an active extension pattern sat more lordotic at the symptomatic lower lumbar spine, whereas patients with a flexion pattern sat more kyphotic, when compared with healthy controls (F = 19.7; df1 = 2, df2 = 63, P < 0.001). Further, NS-CLBP patients had less ability to change their posture when asked to slump from usual sitting (t = 4.2, df = 65; P < 0.001). CONCLUSIONS: Differences in usual sitting posture were only revealed when NS-CLBP patients were subclassified. This highlights the importance of subclassifying NS-CLBP patients.

Adult↗
PubMed2006

Positional MRI changes in supine versus sitting postures in patients with degenerative lumbar spine.

INTRODUCTION: Back pain is associated with a degree of alteration in the alignment and movement of the lumbar spine. The purpose of this study is to investigate how the degree of lumbar segmental degeneration affects sagittal changes in the lumbar spine as it shifts from the supine to the sitting (load-bearing) posture. MATERIALS AND METHODS: Thirty patients with chronic low back pain were enrolled (14 male and 16 female patients); mean age 44.5 years. Their lumbar spines were initially investigated by conventional supine magnetic resonance imaging (MRI) followed later by positional MRI in the seated posture. Of the 150 discs studied, 87 were classified as healthy grade 1, 16 as grade 2, 34 as grade 3, and 13 as grade 4. RESULTS: As the lumbar spine was loaded from the supine to the sitting position, the end-plate angles were decreased significantly as the degeneration was increased. There were also significant changes in the anterior and middle disc heights between the supine and the sitting postures irrespective of the degree of degeneration. The overall lumbar lordosis did not significantly change between the two postures. CONCLUSIONS: We have found that the changes in the segmental motion were related to the degree of degeneration. With positional MRI, we were able to demonstrate changes in healthy and degenerative discs in the weight-bearing position. More similar studies are needed to understand the complex kinematics of the lumbar spine.

Adult↗
PubMedDate not supplied

Early postmenopausal hormone therapy improves postural balance.

OBJECTIVE: Postmenopausal hormone therapy (HT) results in more substantial reductions in the risk of hip fracture when initiated sooner rather than later after menopause. We studied the effects of postmenopausal HT on the postural balance of postmenopausal women, with further assessment according to the time since they achieved menopause. DESIGN: One hundred women with a mean age of 52.5 years (91 evaluable) were randomly and blindly assigned to either a sequential estradiol-norethisterone acetate regimen or placebo for 3 months, after which all participants received open HT for a further 3 months. Postural balance was assessed as sway velocity using a force platform. RESULTS: After 3 months of HT, sway velocity had improved (decreased) from baseline by 7.0% (P = 0.007 vs baseline and P = 0.038 vs placebo). Continued HT for 6 months further improved sway velocity by 12% from baseline (P < 0.0001) to reach values similar to those historically found in younger women or in postmenopausal women after long-term HT. Closer proximity to menopause and more pronounced increases in serum estradiol values were associated with stronger improvements in sway velocity (P = 0.018 for interaction). HT also improved dizziness (P = 0.016 vs baseline and 0.022 vs placebo). (Nonparametric statistics are used throughout, except for analyses of interaction and dizziness.) CONCLUSIONS: Initiation of HT soon after menopause rapidly improved postural balance to levels normally seen in young women. We suggest that improved postural balance can contribute to the protection against fractures associated with HT and explain the more substantial reduction in hip fracture risk after HT initiated sooner, compared with later, after menopause. Further study is required to confirm these results.

Dizziness↗
PubMed2006

Changes in posture and perceived exertion in adolescents wearing backpacks with and without abdominal supports.

OBJECTIVE: The goal was to examine whether backpacks with an abdominal support device improve posture and decrease exertion while walking among adolescents. DESIGN: Double-blinded trial, with 20 subjects, performed at a University Spine Center. On day 1, adolescents walked on a treadmill for 5 mins with photographic measurement of posture and responded to the Borg scale of perceived exertion before and after ambulation. On day 2, they repeated the trial four more times wearing a backpack randomly loaded with either 10% or 20% of body weight and with or without the Back Balancer abdominal support. Postural measures were recorded by a blinded observer. RESULTS: Postural changes (forward lean) wearing a backpack with abdominal support were significantly lower while carrying both 10% and 20% of body weight (P = 0.024 and P = 0.008, respectively) vs. no abdominal support. In addition, perceived exertion at 10% and 20% of body weight was significantly greater without abdominal support (P = 0.042 and P = 0.018, respectively). CONCLUSIONS: Forward lean and perceived exertion while wearing backpacks in adolescents can be significantly decreased with abdominal support. This may increase comfort and decrease complications, such as back pain, that may arise from backpack use.

Abdomen↗
PubMed2000

Renormalization group analysis of a quivering string model of posture control.

Scaling concepts and renormalization group methods are applied to a simple linear model of human posture control consisting of a trembling or quivering string subject to damping and restoring forces. The string is driven by uncorrelated white Gaussian noise, intended to model the corrections of the physiological control system. We find that adding a weak quadratic nonlinearity to the posture control model opens up a rich and complicated phase space (representing the dynamics) with various nontrivial fixed points and basins of attraction. The transition from diffusive to saturated regimes of the linear model is understood as a crossover phenomenon, and the robustness of the linear model with respect to weak nonlinearities is confirmed. Correlations in posture fluctuations are obtained in both time and space domains. There is an attractive fixed point identified with falling. The scaling of the correlations in the front-back displacement, which can be measured in the laboratory, is predicted for both large-separation (along the string) and long-time regimes of posture control.

Humans↗