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PubMed2005

Postural strategy changes with fatigue of the lumbar extensor muscles.

The purpose of this study was to investigate the effect of lumbar extensor fatigue on postural strategy in response to a balance perturbation. Anteriorly-directed force perturbations were applied to the upper back with a padded pendulum and attempted to challenge the postural control system without eliciting a stepping response. In three separate sessions, subjects were perturbed both before and after a fatiguing protocol that induced lumbar extensor fatigue to one of three different fatigue levels. Postural strategy was quantified using center of pressure position along with joint angles and joint torques for the ankle, knee, hip, and "low back" joints. Results showed both proactive and reactive changes in postural strategy. Proactive changes involved a slight anterior lean prior to the perturbation, and reactive changes were consistent with a shift toward more of a hip strategy with fatigue. In addition, results suggested that subjects classified as moving mostly at the hip prior to fatigue were more affected by fatigue compared to subjects classified as moving roughly equal amounts at the ankle and hip prior to fatigue. Increasing fatigue level exaggerated some, but not all, of the changes in postural strategy with fatigue. These findings illustrate that neuromuscular fatigue can influence postural strategy in response to a balance perturbation.

Adult↗

PubMed2004

Kinematic and kinetic validity of the inverted pendulum model in quiet standing.

Movements of the whole-body center of mass during quiet standing have been estimated from measurements of body segment movements. These whole-body center of mass movements have been compared with movements of the center of mass as predicted from a simple inverted-pendulum model of standing. However, the total body center of mass is a weighted average of the center of mass of all individual body segments. The question arises as to how well the total body center of mass represents the individual segments and lower limb joint angles. This study focuses on the validity of how well the individual segments and lower limb angles temporally and spatially synchronize with the total body center of mass. Eleven healthy university students volunteered to participate. Kinematic data were collected using a 3D optoelectronic camera system; kinetic data were collected using a 3D force plate. Participants stood quietly, with eyes open, for 120 s. Segment and whole body centers of mass were calculated from a 14 segment, 3D bilateral model. Segment and joint angles were calculated for the lower limbs, bilaterally, and the trunk. Segment center of mass root-mean-square displacements were strongly correlated with center of mass height relative to the ankle joint and were synchronized, or temporally locked, to the movement of the whole body center of mass. Sagittal plane ankle angular displacements were highly correlated to sagittal plane center of mass movement; stronger correlations between body center of mass and lower limb angular displacement were observed, the result of compensatory knee joint angular displacements. These data support and extend the use of an inverted pendulum model to represent quiet standing postural control.

Acceleration↗

PubMed1999

Biological reaction to vibration--implications for sport.

In many situations of everyday life, vibration load occurs. Here whole body vibration in vehicles, such as boats, cars, helicopters and others as well as hand-transmitted vibration (motor saws etc.) can be named. As vibration is assumed liable to cause various threats to human health, a great number of studies in work science focussed on dose-effect relations and concepts for prevention. Although in many sports remarkable vibration load also occurs, there is very little research on the potential dangers and benefits of vibration stimuli, e.g. on whole body vibration and the implications for muscular activity and neuromuscular control in sport. In personal studies the damping behaviour and training effects under whole body vibration were investigated. Various research areas have been studied in order to approach the relevant topics: neuromuscular and posture control, energy metabolism in terms of oxygen uptake under whole body vibration and local concentration of phosphates by means of 31P-MRS. Furthermore the effects of a strength training under whole body vibration were analysed. The results underline that vibration is a neglected research topic in sport science from the preventive point of view as well as from the one focussing on the improvement of sport performance.

Energy Metabolism↗

PubMedDate not supplied

Comparison of head- and body-velocity trajectories during locomotion among healthy and vestibulopathic subjects.

The optimal strategies for improving locomotor stability in people with vestibulopathy remain unclear. To help identify likely targets for intervention, we sought to determine whether vestibulopathic postural control impairment during locomotor activity was more localized to either the head or the whole body. We used high curvature analysis (HCA) to quantify the smoothness of head- and body-velocity trajectories during repeated stepping in 18 vestibulopathic and 17 healthy subjects. We employed a mixed-model repeated measures analysis of variance to compare differences in head- and body-trajectory HCA scores. Pearson coefficients were used to describe relationships between head- and body-trajectory HCA scores within each group. The results revealed that neither head- nor body-velocity trajectories were relatively more impaired in subjects with vestibulopathy. Importantly, however, the smoothness of head and body trajectories was more strongly related in subjects with vestibulopathy compared with healthy subjects, suggesting that the fundamental motor control impairment produced by vestibulopathy may be related to an abnormal coupling of head and body motion. We discuss implications for locomotor training in patients with vestibulopathy.

Adult↗

PubMed1998

A new method for evaluating motor control in gait under real-life environmental conditions. Part 2: Gait analysis.

OBJECTIVE: The validity of assessing balance in gait by measuring balance in standing is questionable. Better methods for measuring balance during walking are therefore needed. DESIGN: It is suggested that the individual will demonstrate adequate postural control by moving a reference point near the body centre of mass (CoM) smoothly towards an intentional goal, even though movements of the extremities show variability consistent with a changing environment. BACKGROUND: In spite of an increased interest in variability as a prerequisite for motor control, gait analysis methods focus, to a large extent, on symmetry and repeatability of movements in stereotyped settings. METHODS: Acceleration of a reference point over the lumbar spine is registered during walking by a portable, triaxial accelerometry system. RESULTS: A quadratic relation between acceleration root mean square (RMS) and walking speed is demonstrated, and a second degree polynomial can therefore be computed as a curve estimate, if acceleration RMS representing at least three walking speeds are available. CONCLUSIONS: The relation between acceleration over a reference point on the trunk and walking speed can be compared between trials and also when walking speeds are self-selected. Calibration procedures and testing of the instrument for precision and accuracy in a mechanical testing jig are described in a companion article. RELEVANCE: This study suggests a new alternative to the traditions of measuring balance in standing and movements of the legs in walking. The method allows balance in gait to be assessed at self-selected speeds in relevant environmental conditions, which may facilitate gait analysis in the clinic and improve the validity of the results.

Journal Article↗

PubMed2004

Exercise for health for early postmenopausal women: a systematic review of randomised controlled trials.

Women who pass menopause face many changes that may lead to loss of health-related fitness (HRF), especially if sedentary. Many exercise recommendations are also relevant for early postmenopausal women; however, these may not meet their specific needs because the recommendations are based mainly on studies on men. We conducted a systematic review for randomised, controlled exercise trials on postmenopausal women (aged 50 to 65 years) on components of HRF. HRF consists of morphological fitness (body composition and bone strength), musculoskeletal fitness (muscle strength and endurance, flexibility), motor fitness (postural control), cardiorespiratory fitness (maximal aerobic power, blood pressure) and metabolic fitness (lipid and carbohydrate metabolism). The outcome variables chosen were: bodyweight; proportion of body fat of total bodyweight (F%); bone mineral density (BMD); bone mineral content (BMC); various tests on muscle performance, flexibility, balance and coordination; maximal oxygen consumption (V-dotO(2max)); resting blood pressure (BP); total cholesterol (TC); high-density lipoprotein-cholesterol; low-density lipoprotein-cholesterol; triglycerides; blood glucose and insulin. The feasibility of the exercise programme was assessed from drop-out, attendance and injury rates. Twenty-eight randomised controlled trials with 2646 participants were assessed. In total, 18 studies reported on the effects of exercise on bodyweight and F%, 16 on BMD or BMC, 11 on muscular strength or endurance, five on flexibility, six on balance or coordination, 18 on V-dotO(2max), seven on BP, nine on lipids and two studies on glucose an one on insulin. Based on these studies, early postmenopausal women could benefit from 30 minutes of daily moderate walking in one to three bouts combined with a resistance training programme twice a week. For a sedentary person, walking is feasible and can be incorporated into everyday life. A feasible way to start resistance training is to perform eight to ten repetitions of eight to ten exercises for major muscle groups starting with 40% of one repetition maximum. Resistance training initially requires professional instruction, but can thereafter be performed at home with little or no equipment as an alternative for a gym with weight machines. Warm-up and cool-down with stretching should be a part of every exercise session. The training described above is likely to preserve normal bodyweight, or combined with a weight-reducing diet, preserve BMD and increase muscle strength. Based on limited evidence, such exercise might also improve flexibility, balance and coordination, decrease hypertension and improve dyslipidaemia.

Absorptiometry, Photon↗

PubMed2006

Threshold control of motor actions prevents destabilizing effects of proprioceptive delays.

It is usually assumed that proprioceptive feedback comes to motoneurons too late to contribute to the initial activity of agonist muscles during fast arm movements, leading to the suggestion that this feedback is only efficient in slow movements and postural control. The argument does not take into account that the changes in the motoneuronal membrane potentials and the associated changes in the state of spinal neurons preceding the initial activity of muscles deeply affect, in a forward way, the state of reflex systems by shifting their thresholds, as suggested in the lambda model for motor control. As a result, the initial muscle activity emerges with full contribution of these systems so that the effects of reflex delays become negligible. We tested the hypothesis that threshold control of muscle activation may be instrumental in preventing destabilizing effects of proprioceptive delays in spinal and trans-cortical pathways to motoneurons. The analysis was made by recording fast elbow movements (peak velocity approximately 300-500 degrees/s) and simulating them in a dynamic model that incorporates the notion of threshold control of intrinsic and reflex muscle properties. The model was robust in reproducing experimental movement patterns (R (2)>0.95). It generated stable output despite substantial proprioceptive (up to 100 ms) and electromechanical (40 ms) delays. Stability was thus ensured for delays not only in segmental (about 25-50 ms) but also in trans-cortical loops (50-70 ms). Our study illustrates that a natural physiological process--threshold control--may manifest feed-forward properties hitherto attributed to hypothetical internal neural models.

Adult↗

PubMed1995

Head and trunk movements in the frontal plane during complex dynamic equilibrium tasks in humans.

Eight normal human subjects were asked to maintain monopodal equilibrium on a narrow beam (task 1) or bipodal equilibrium on an unstable rocking platform (task 2) for 5 s. Each task was performed under four experimental conditions: (1) in light, (2) in darkness, (3) in light while subject had to hold a full cup of water, and (4) as in 3, but with additional instructions to fix the gaze on the cup. The movements of the trunk and head in the frontal plane were recorded by means of a 50-Hz TV image analyzer that computed the coordinates of small reflective markers glued on the skin of the subjects. On the beam the trunk was inclined on the side of the supporting foot (13 +/- 9 degrees), on the rocking platform the mean trunk orientation during the tests was nearly vertical (2 +/- 7 degrees). Nevertheless, in both tasks the mean head position was the same and close to vertical: 1.5 +/- 4 degrees on the rocking platform and 1.5 +/- 5 degrees on the beam. For both tasks and all experimental conditions the head remained stabilized relative to vertical, despite large translations in the frontal plane. Standard deviations of head orientation from its mean value were 2.8 +/- 2 degrees for task 1 and 2 +/- 1.5 degrees for task 2. The changes of trunk orientation were significantly higher: 6.2 +/- 4.8 degrees and 4.5 +/- 4 degrees, respectively. The differences in angular stability of head and trunk, measured through the standard deviations of angular displacements, were especially pronounced in trials with large trunk movements. It was concluded that head angular stabilization, providing the central nervous system with necessary visual and vestibular references, is essential for effective dynamic postural control in the frontal plane during complex equilibrium tasks.

Adult↗

PubMed1986

Conditioning of crossed extensor reflex pathways by independent natural stimulation of labyrinth, neck and elbow joint afferents.

The present experiments demonstrated that labyrinth, neck and elbow joint afferents interact to influence the excitability of crossed extensor reflex pathways projecting to triceps brachii in decerebrate cats. Reflex excitability was dependent on head, neck and elbow position such that it was increased when the elbow was held at full flexion and either the head maintained side down or the neck rotated side up. Such interaction between these afferents is likely to be important in postural control.

Animals↗

PubMed2004

Vestibulo-ocular physiology underlying vestibular hypofunction.

The vestibular system detects motion of the head and maintains stability of images on the fovea of the retina as well as postural control during head motion. Signals representing angular and translational motion of the head as well as the tilt of the head relative to gravity are transduced by the vestibular end organs in the inner ear. This sensory information is then used to control reflexes responsible for maintaining the stability of images on the fovea (the central area of the retina where visual acuity is best) during head movements. Information from the vestibular receptors also is important for posture and gait. When vestibular function is normal, these reflexes operate with exquisite accuracy and, in the case of eye movements, at very short latencies. Knowledge of vestibular anatomy and physiology is important for physical therapists to effectively diagnose and manage people with vestibular dysfunction. The purposes of this article are to review the anatomy and physiology of the vestibular system and to describe the neurophysiological mechanisms responsible for the vestibulo-ocular abnormalities in patients with vestibular hypofunction.

Adult↗

PubMed1986

Haemodynamic effects of vasopressin in man are related to posture.

Ten healthy volunteers received intravenous infusions of arginine vasopressin (AVP) at 0.1 m-unit min-1 kg-1 and 5% D-glucose on separate days. AVP caused a small fall in forearm blood flow and small rises in mean arterial pressure and systemic vascular resistance. Cardiac output was unaffected. When subjects were tilted to 50 degrees the fall in forearm blood flow was much greater, mean fall being 44.8% with AVP compared with 18.2% with D-glucose. Cardiac output also fell significantly more with AVP, and diastolic pressure, mean arterial pressure and systemic vascular resistance rose significantly more on tilting during AVP infusion than with D-glucose. Six of the same volunteers were given sequential infusions of 'low dose' (0.0125 m-unit min-1 kg-1) and 'high dose' (0.3 m-unit min-1 kg-1) AVP on a third occasion. Tilting still produced a mean fall in forearm blood flow of 41.2% during low dose infusion, despite a mean plasma AVP level of only 1.9 pg/ml, which is well within the physiological range. When the AVP concentration was increased 24-fold to the high dose, forearm blood flow fell only a further 8.8%. The low dose infusion was also associated with a marked fall in cardiac output on tilting and a rise in systemic vascular resistance. We conclude that AVP has profound haemodynamic effects in man at physiological concentrations. Although these effects are modest in the supine position, they become marked on tilting, suggesting a possible role for AVP in the postural control of blood pressure.

Adult↗

PubMed1998

Physiological principles of vestibular function on earth and in space.

Physiological mechanisms underlying vestibular function have important implications for our ability to understand, predict, and modify balance processes during and after spaceflight. The microgravity environment of space provides many unique opportunities for studying the effects of changes in gravitoinertial force on structure and function of the vestibular system. Investigations of basic vestibular physiology and of changes in reflexes occurring as a consequence of exposure to microgravity have important implications for diagnosis and treatment of vestibular disorders in human beings. This report reviews physiological principles underlying control of vestibular processes on earth and in space. Information is presented from a functional perspective with emphasis on signals arising from labyrinthine receptors. Changes induced by microgravity in linear acceleration detected by the vestibulo-ocular reflexes. Alterations of the functional requirements for postural control in space are described. Areas of direct correlation between studies of vestibular reflexes in microgravity and vestibular disorders in human beings are discussed.

Acceleration↗

PubMed2002

Effects of postural muscle fatigue on the relation between segmental posture and movement.

The purpose of this study was to examine whether fatigue of postural muscles might influence the coordination between segmental posture and movement. Seven healthy adults performed series of fifteen fast wrist flexions and extensions while being instructed to keep a dominant upper limb posture as constant as possible. These series of voluntary movements were performed before and after a fatiguing submaximal isometric elbow flexion, and also with or without the help of an elbow support. Surface EMG from muscles Deltoïdeus anterior, Biceps brachii, Triceps brachii, Flexor carpi ulnaris, Extensor carpi radialis were recorded simultaneously with wrist, elbow and shoulder accelerations and wrist and elbow displacements. Fatigue was evidenced by a shift of the elbow and shoulder muscles EMG spectra towards low frequencies. Kinematics of wrist movements and corresponding activations of wrist prime-movers, as well as the background of postural muscle activation before wrist movement were not modified. There were only slight changes in timing of postural muscle activations. These data indicate that postural fatigue induced by a low-level isometric contraction has no effect on voluntary movement and requires no dramatic adaptation in postural control.

Adult↗

PubMed2005

Motor and postural response profiles of four children with developmental coordination disorder.

PURPOSE: The purpose of this report is to present a descriptive profile of the postural responses and motor skill performance of four children with developmental coordination disorder (DCD). METHODS: Four children with DCD, aged nine to 12 years participated. A profile of each child's case background, school performance, and motor skill performance was developed, in addition to the collection of data from three sessions of posturography trials on the computerized Sensory Organization Test (SOT). RESULTS: All four children had a significant degree of impairment in balance responses and limitations in motor performance, with increased sway and frequency of falls in all sensory conditions on the SOT in comparison with peers. Mean equilibrium scores were between one and two standard deviations below peer averages, and sensory scores showed performance levels similar to those of younger age groups. There was a high level of variability associated with repeated SOTs. CONCLUSIONS: The SOT data provide further insight into the underlying mechanisms that contribute to balance deficits experienced by children with DCD and suggest that assessment and therapeutic approaches take into account sensory deficits in postural control.

Case-Control Studies↗

PubMed1996

Effect of forward lean on postural ankle dynamics.

Previous studies investigating postural control using platform perturbations demonstrated that forward leaning occurs under certain experimental conditions. This study examined a potential benefit of forward leaning, investigating the hypothesis that forward lean acts to increase the effective stiffness of the postural ankle dynamics. A systems modeling approach was used to evaluate the effect of forward lean (4 degrees ankle flexion beyond normal stance) on dynamic postural responses to continuous random antero-posterior platform acceleration in four healthy young adults. Motion was limited to the ankle joint using a restraint device and responses were characterized in terms of center-of-pressure displacement. Also, EMG and kinematic data were used to partition measured ankle torque into impedance and activation (postural "reflex") components. The results failed to show a consistent effect, due to lean, on the ankle dynamics. A significant increase in phasic ankle torque due to increased muscle impedance during forward lean was counterbalanced by a comparable decrease in net "reflex" ankle torque. The change in "reflex" torque was apparently due to decreased phasic dorsiflexor activity in forward lean, since phasic plantarflexor activity did not change significantly. Functionally, the results suggest that forward lean occurs for reasons other than stiffening of the overall postural ankle dynamics.

Adult↗

PubMed2000

Abnormal air-righting reflex in striatal rats.

To understand dynamic postural control of the higher brain, we compared air-righting reflexes in various decerebrate rats. Post-operative 3-5 d thalamic and mesencephalic rats displayed almost similar righting movements as intact. However, in striatal animals, coordination of righting movements was disrupted. The higher brain without cortical control could interfere with the brainstem center of the air-righting reflex.

Animals↗

PubMed2026

The effect of combining visuo-vestibular exercises with manual therapy and exercise on sensorimotor function in chronic neck pain: A randomized controlled trial.

OBJECTIVE: To investigate whether adding visuo-vestibular exercises to standard manual therapy and exercise produces superior improvements in sensorimotor function, pain, balance, and functional disability in adults with chronic neck pain. METHODS: This prospective, randomized controlled trial enrolled 58 adults with chronic neck pain (≥3 months) allocated to a manual therapy and exercise group (MtE; n = 29) or MtE plus visuo-vestibular exercises (MtE-VVE; n = 29). Both groups completed 12 supervised sessions over six weeks with a daily home exercise programme. Outcomes were assessed at baseline, 6 weeks, and 12 weeks, and included pain intensity (Visual Analog Scale [VAS]), upper extremity reaction time, computerized posturography, the Neck Disability Index (NDI), and cervical muscle endurance. RESULTS: Fifty-four participants (27 per group) completed the study. Both groups improved significantly across all outcomes (p < 0.001). At 12-week follow-up, the MtE-VVE group demonstrated superior outcomes: activity-related pain was reduced by an additional 2.00 cm (95% CI: 0.75-3.25; p = 0.005), bilateral reaction time improved by 1.70 s (p = 0.001), eyes-open mediolateral sway decreased by 0.50 mm (p < 0.001), NDI score was 6.30 points lower (95% CI: 3.42-9.18; p < 0.001), and cervical flexion and extension endurance improved by 12.00 s and 27.70 s, respectively (p ≤ 0.020). CONCLUSION: Adding visuo-vestibular exercises to standard manual therapy and exercise produces clinically meaningful and sustained improvements in activity-related pain, sensorimotor function, postural control, and functional disability in adults with chronic neck pain, and may be recommended as an effective adjunctive intervention.

Humans↗

PubMedDate not supplied

Long-term postural abnormalities in benign paroxysmal positional vertigo.

Benign paroxysmal positional vertigo (BPPV) is a disorder in which patients suffer from acute rotatory vertigo due to the presence of free otoconial debris migrating into one or more semicircular canals during head movements and resulting in abnormal stimulation of the ampullary crest. A prolonged loss of equilibrium of unclear origin is also present. Static posturography is a useful tool for the study of postural control systems and their role in these abnormalities. The aim of the present study was to evaluate the frequency of body sway and long-term instability of BPPV patients by posturography frequency analysis. Twenty patients with canalithiasis of the posterior semicircular canal and 20 normal controls were subjected to static posturography. Informed consent was obtained from all subjects. Patients were tested 1 h after diagnosis, and 3 days and 12 weeks after the characteristic Epley repositioning maneuver. Patients with BPPV showed significantly increased body sway both on lateral (X) and anteroposterior (Y) planes compared to normal subjects. Corporal oscillation with a broad-frequency spectrum was observed in both closed and open eye tests. The repositioning maneuver decreased the X plane body sway, while the anteroposterior sway was unchanged. Twelve weeks after treatment, a normalization of the anteroposterior sway was observed. Results of this study suggest that the long-term postural disturbance associated with BPPV differs from the acute disequilibrium that subsides after canalith repositioning: the former is a sagittal plane/broad spectrum body sway, while the latter is primarily a frontal plane/low frequency sway. The Epley maneuver was shown to reduce frontal sway, a postural abnormality that might therefore be linked to posterior semicircular canal function. Conversely, the observed sagittal body sway was only partially relieved by the restoration of canal function, and therefore, may be more related to the chronic dizziness observed in these patients.

Adult↗