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PubMed2005

Motor strategies responsible for maintaining standing posture after deafferentation of the unilateral leg.

OBJECTIVE: To identify the motor strategies responsible for maintaining standing posture after deafferentation of the unilateral leg. DESIGN: Pretest-posttest, repeated-measures design. SETTING: A Japanese university hospital rehabilitation facility. PARTICIPANTS: Nine healthy subjects aged 25 to 32 years. INTERVENTION: Two separate sessions that consisted of prolonged standing (control task) and standing until the H-reflex disappeared through the application of an inflated pneumatic cuff above the right knee. MAIN OUTCOME MEASURES: Center of pressure (COP), hip and ankle joint positions, and electromyographic activities. RESULTS: In the control task, no time-related change during prolonged standing was found in any of the measured parameters. After deafferentation, the right soleus activity decreased significantly (P<.01), so the mean velocities of the COP in the anteroposterior and mediolateral directions were greater and the average COP position under the right foot shifted backward compared with those in the previous periods (P<.01). Also, the left tibialis anterior and soleus were activated, as was the bilateral gluteus medius. CONCLUSIONS: The unilateral loss of leg and foot sensory information necessitated additional regulatory activities to stabilize the standing posture. The newly organized posture appeared to partly simulate the standing posture in patients with sensory disturbance of a unilateral leg.

Adult↗
PubMed2006

Effect of different sitting postures on lung capacity, expiratory flow, and lumbar lordosis.

OBJECTIVE: To investigate the effect of sitting posture on lung capacity and expiratory flow (LC-EF) and lumbar lordosis. DESIGN: Repeated measures on 1 group of subjects in 4 postures. SETTING: Laboratory. PARTICIPANTS: Seventy able-bodied volunteers. INTERVENTIONS: Postures were assumed randomly: normal, with full ischial support and flat lumbar support; slumped, with the pelvis positioned in the middle of seat while leaning against the backrest; against the back part of the seat without ischial support (WO-BPS), with partially removed ischial support and an enhanced lumbar support; and standing. MAIN OUTCOME MEASURES: For LC-EF, forced vital capacity, maximum forced expiratory flow, forced expiratory volume in 1 second, and peak expiratory flow; and lumbar lordosis. RESULTS: All LC-EF measures in standing were significantly superior to those in slumped and normal sitting, and 4 measures were significantly higher than in WO-BPS. In slumped sitting, LC-EF significantly decreased from that in normal sitting. WO-BPS sitting significantly increased 4 of the LC-EF measures from those in the normal sitting. Lumbar lordosis was the highest in standing and progressively decreased in WO-BPS, normal, and slumped sitting. CONCLUSIONS: Slumped sitting significantly decreased LC-EF and lumbar lordosis. Because it increases the lumbar lordosis and promotes LC-EF, the WO-BPS posture may be a better seating option for people sitting for a prolonged time.

Adult↗
PubMed2006

Risk-factor analysis of high school basketball-player ankle injuries: a prospective controlled cohort study evaluating postural sway, ankle strength, and flexibility.

OBJECTIVE: To analyze risk factors, including postural sway, ankle strength, and flexibility, for the prediction of ankle injuries in men's high school basketball players. DESIGN: A cohort study with follow-up duration of 1 basketball season. SETTING: Biomechanics laboratory. PARTICIPANTS: Forty-two (age, 16.5+/-1.1y) players competing in first league of the High School Basketball Association without history of injury in the lower extremities within 6 months before recruitment and without significant malalignment in the lower extremities were included. None of these players met exclusion criteria such as using ankle braces or taping or failed in wearing low-top sports shoes during the follow-up season. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Biomechanic measurements including isokinetic ankle strength, 1-leg standing postural sway, and ankle joint dorsiflexion flexibility were performed before the basketball season by 1 physical therapist. The subsequent monthly follow-up questionnaires were sent and returned by mail to prospectively record the incidence of ankle injury occurring in the season. Results of these preseason measurements were analyzed to correlate if any of these measured variables could predict future ankle injuries. RESULTS: Eighteen ankle sport injuries were recorded for 42 players during the follow-up season. High variation of postural sway in both anteroposterior and mediolateral directions corresponded to occurrences of ankle injuries (P=.01, odds ratio [OR]=1.220; P< .001, OR=1.216, respectively). All other variables were not associated with injury. CONCLUSIONS: High variations of postural sway in 1-leg standing test could explain partly the increased prevalence of ankle injury in basketball players. It may be used as a screening tool to recommend balance training before basketball season.

Adolescent↗
PubMed2005

Sexually dimorphic postural adjustments are used in a skilled reaching task in the rat.

Sex differences occur not only in the sexual repertoire of animals but also are evident in other aspects of movement. The present study asked whether sexually dimorphic motor behavior extends to the skilled movements used in reaching for food in the rat. Because we have previously shown that males and females are sexually dimorphic in their organization of lateral and rotatory movements and because postural adjustments are incorporated into skilled movements, both body posture and limb movements were examined during a skilled reaching task. Male and female Long-Evans rats were filmed, from both the front and ventral views and their stepping patterns, postural adjustments and forelimb movements, during a successful reach were analyzed. While males and females did not differ in forelimb movements, they were significantly different in how they approached and oriented their body to the food item during a successful reach. These results are discussed in relation to the dissociation of skilled movement from postural adjustments, sex-dependent alterations following CNS injury, and the neural and evolutionary basis of sex differences in movement organization.

Animals↗
PubMed2004

Emotion and motivated behavior: postural adjustments to affective picture viewing.

Thirty-six participants (18 female, 18 male) viewed affective pictures to investigate the coupling between emotional reactions and motivated behavior. Framed within the biphasic theory of emotion, the three systems approach was employed by collecting measures of subjective report, expressive physiology, and motivated behavior. Postural adjustments associated with viewing affective pictures were measured. Results indicated sex-differences for postural responses to unpleasant pictures; an effect not found for pleasant and neutral picture contents. Females exhibited increased postural movement in the posterior direction, and males exhibited increased movement in the anterior direction, for unpleasant pictures. Subjective report of valence and arousal using the self-assessment manikin (SAM), and the startle eye-blink reflex were collected during a separate session, which replicated previous picture-viewing research. Specifically, participants rated pleasant pictures higher in valence and exhibited smaller startle responses compared to unpleasant pictures. Females also reported lower valence ratings compared to males across all picture contents. These findings extend our knowledge of motivated engagement with affective stimuli and indicate that postural responses may provide insight into sex-related differences in withdrawal behavior.

Adolescent↗
PubMed2005

Rest and postural tremors in patients with Parkinson's disease.

The mild tremor of twenty-four patients with Parkinson's disease (PD) was quantified in four conditions: finger-rest, finger-postural, hand-rest and hand-postural. Tremor characteristics such as amplitude, median power frequency, power dispersion, and power percentage within the 4-7 Hz band were correlated across conditions. Results show that all tremor characteristics were well correlated across conditions (Spearman's Rank), signifying that presence of PD rest tremor was accompanied with a postural tremor having similar characteristics to that of rest tremor. The present results suggest that neural mechanisms involved in PD rest tremor do remain active in the postural condition, even in patients with mild tremor.

Aged↗
PubMed2006

Postural adaptation to walking on inclined surfaces: II. Strategies following spinal cord injury.

OBJECTIVE: To investigate the postural adaptations to inclined walking in spinal cord injured (SCI) subjects. METHODS: Eight subjects with an incomplete spinal cord injury and eight age- and sex-matched healthy control subjects walked on a treadmill at five different grades (from -10 to 10%) without any assistance. The movements of the trunk and pelvis were recorded with four high-resolution cameras. RESULTS: The SCI subjects walked with greater forward tilt of both trunk and pelvic segments during level or inclined walking and could not adapt their body orientation to the inclination of the support surface as observed in healthy control subjects. Trunk and pelvic rotations as well as lateral excursions were maintained constant during inclined walking in both groups of subjects but total excursions were always greater in the SCI subjects. CONCLUSIONS: We argue that the forward bending posture observed in SCI subjects at any treadmill grade is adopted to compensate for a certain degree of instability due to lower-limb deficits and is a postural adaptation to the daily use of ambulatory assistive devices. SIGNIFICANCE: The bent posture adopted by SCI subjects is not adequate when performing level or downhill walking and can lead to a loss of balance or a fall in these subjects.

Adaptation, Physiological↗
PubMed2005

Sequencing sit-to-stand and upright posture for mobility limitation assessment: determination of the timing of the task phases from force platform data.

The identification of quantitative tools to assess an individual's mobility limitation is a complex and challenging task. Several motor tasks have been designated as potential indicators of mobility limitation. In this study, a multiple motor task obtained by sequencing sit-to-stand and upright posture was used. Algorithms based on data obtained exclusively from a single force platform were developed to detect the timing of the motor task phases (sit-to-stand, preparation to the upright posture and upright posture). To test these algorithms, an experimental protocol inducing predictable changes in the acquired signals was designed. Twenty-two young, able-bodied subjects performed the task in four different conditions: self-selected natural and high speed with feet kept together, and self-selected natural and high speed with feet pelvis-width apart. The proposed algorithms effectively detected the timing of the task phases, the duration of which was sensitive to the four different experimental conditions. As expected, the duration of the sit-to-stand was sensitive to the speed of the task and not to the foot position, while the duration of the preparation to the upright posture was sensitive to foot position but not to speed. In addition to providing a simple and effective description of the execution of the motor task, the correct timing of the studied multiple task could facilitate the accurate determination of variables descriptive of the single isolated phases, allowing for a more thorough description of the motor task and therefore could contribute to the development of effective quantitative functional evaluation tests.

Adult↗
PubMed2006

Attentional demands of postural control: the ability to selectively allocate information-processing resources.

Most studies have suggested the process of recovering body stability requires information-processing resources, but whether adults have the ability to selectively allocate resources to maintain balance is not known. Using a variable priority dual-task paradigm the present experiment investigated the extent to which young adults are able to shift attention between a postural task and a visual spatial memory task. Our results demonstrated a significant difference in verbal response time dependent on instructional set (focus on visual spatial memory versus postural task) but no difference in body sway measurement, indicating the ability of young adults to modulate visual spatial memory task, but not postural task focus. This suggests the existence of a hierarchy within attentional tasks with postural stability being a priority to stabilize gaze and head position.

Adult↗
PubMed2006

The influence of ambient lighting levels on postural sway in healthy children.

The purpose of this study was to determine whether postural sway in healthy children varied in different levels of ambient lighting. Twelve boys and 26 girls with a mean age of 118 months stood on a force platform under three conditions: eyes closed, eyes opened in regular light (200 lx) and eyes opened in dim light (3 lx). Analysis of variance and pairwise comparisons revealed significantly more postural sway with the eyes closed condition compared to the regular and dim light conditions but no differences between the regular and dim light conditions. While our results on postural sway during the eyes closed condition are consistent with current findings in the pediatric and adult literature, our findings comparing postural sway during regular and dim light conditions differ from those found in older adults. It appears that the visual system of children is efficient in dim light conditions, adding support to the view that quiet standing is more dependent on vision in older adults than in younger individuals.

Analysis of Variance↗
PubMed2005

Postural control in otolith disorders.

It was the aim of the present paper to investigate the influence of otolith disorders on human postural control by different methods. The 33 patients of our study had undergone a minor head injury and suffered subsequently from an utricular or sacculo-utricular disorder as evidenced by vestibular evoked myogenic potential recordings and eccentric rotation recordings of the otolith-ocular responses. Postural control was assessed by performing stance/gait tests (standard balance deficit test, SBDT) and by evaluating trunk sway (using angular velocity sensors). Moreover, classical tests of the posterior column of the spinal tract (Romberg/Unterberger) and the dynamic posturography (sensory organization test, SOT) were included. It could be shown that SBDT tasks with reduced proprioceptive and visual cues (e.g. standing on foam, eyes closed) are most sensitive for an otolith disorder. The patients showed an increased trunk sway in the pitch plane (i.e. linear motion as adequate utricular stimulus) and an increase in sway velocities (i.e. tilting movements as adequate saccular stimulus) compared to controls. The SOT was most sensitive for combined (sacculo-utricular) otolith disorders (78%) while vestibulospinal tests are not enough sensitive. In essence, otolith disorders evidently impair human postural control and have been possibly underestimated as a source of posttraumatic postural imbalance as yet.

Adult↗
PubMed2005

Integration of posture and movement: contributions of Sherrington, Hess, and Bernstein.

Neural mechanisms that integrate posture with movement are widespread throughout the central nervous system (CNS), and they are recruited in patterns that are both task- and context-dependent. Scientists from several countries who were born in the 19th century provided essential groundwork for these modern-day concepts. Here, the focus is on three of this group with each selected for a somewhat different reason. Charles Sherrington (1857-1952) had innumerable contributions that were certainly needed in the subsequent study of posture and movement: inhibition as an active coordinative mechanism, the functional anatomy of spinal cord-muscle connectivity, and helping set the stage for modern work on the sensorimotor cortex and the corticospinal tract. Sadly, however, by not championing the work of his trainee and collaborator, Thomas Graham Brown (1882-1965), he delayed progress on two key motor control mechanisms: central programming and pattern generation. Walter Hess (1881-1973), a self-taught experimentalist, is now best known for his work on CNS coordination of autonomic (visceral) and emotional behavior. His contributions to posture and movement, however, were also far-reaching: the coordination of eye movements and integration of goal-directed and "framework" (anticipatory set) motor behavior. Nikolai Bernstein (1896-1966), the quintessence of an interdisciplinary, self-taught movement neuroscientist, made far-reaching contributions that were barely recognized by Western workers prior to the 1960s. Today, he is widely praised for showing that the CNS's hierarchy of control mechanisms for posture and movement is organized hand-in-hand with distributed and parallel processing, with all three subject to evolutionary pressures. He also made important observations, like those of several previous workers, on the goal focus of voluntary movements. The contributions of Sherrington, Hess, and Bernstein are enduring. They prompt thought on the philosophical axioms that appear to have driven their research, and the continual need for emphasis on interdisciplinary, comparative, and transnational approaches to advance movement neuroscience.

Affect↗
PubMed2006

Effects of postural anxiety on the soleus H-reflex.

Previous research has proposed that spinal reflex modulation may mediate anxiety-related changes in postural control. This study investigated how soleus H-reflex amplitude was influenced by standing at heights that induced different levels of anxiety. H-reflexes were elicited in 15 participants standing at the center and edge of a platform raised from a low to a high height (with and without vision). Increased skin conductance confirmed the anxiety effect of elevated surface heights. When standing at the edge of the platform with vision, H-reflex amplitude was attenuated in the high compared to low height condition. Changes in background muscle activity could not explain observed H-reflex changes, suggesting the potential involvement of pre-synaptic inhibition or fusimotor drive on anxiety-related changes in reflex modulation. This study reveals that healthy participants reduce spinal reflex excitability in the presence of increased postural anxiety and a postural threat imposed by standing at the edge of a raised platform. These findings have implications for understanding control of standing balance in individuals with postural instability and/or fear of falling, such as the elderly or stroke.

Adult↗
PubMed2004

Hip-flexed postures do not affect local anaesthetic spread following induction of epidural analgesia for labour.

Hip-flexed postures enlarging the pelvic diameter are used to improve the obstetric course of labour. Although most investigations show that lateral and sitting positions do not affect the spread of epidural analgesia, the effect of recently introduced hip-flexed postures has yet to be confirmed. This prospective randomised study included 93 parturients. Ropivacaine 0.1% 12 mL plus sufentanil 0.5 micrograms/mL was administered epidurally over a period of 6 min in one of four postures: sitting, right hip-flexed left lateral position, left hip-flexed right lateral position and supine 30 degrees lateral tilt as a control group. Left and right cephalad and sacral epidural spread were measured every 2 min over a period of 30 min. Pain relief, motor blockade and maternal and fetal side effects were noted. The total epidural spread was 15+/-0.3 dermatomes and the upper level of thermo-algesic blockade T7-T8 (range T3 to T10) in all groups. There were no differences between groups in left or right total spread or upper level of epidural blockade, time to maximal block or pain relief. There was no motor block nor any maternal or fetal side effects. The power of the study (1 - beta) was 93%. We conclude that, for the three hip-flexed postures tested, position does not influence local anaesthetic spread or symmetry of thermo-algesic blockade after induction of obstetric epidural analgesia.

Adult↗
PubMed2005

Postural and eye-blink indices of the defensive startle reflex.

Postural and eye-blink reactions to acoustic startle probes were examined in 24 volunteers, who completed two blocked conditions (baseline, startle). A postural reaction during the startle condition demonstrated a reflexive movement in the anterior-posterior direction, which was not observed during the baseline condition. This reflexive response was positively associated with the eye-blink reflex, such that larger blink magnitude related to greater posterior movement. These findings were not observed for postural movements in the medial-lateral direction. The results suggest that a measurable postural reaction may be observed following a startling acoustic stimulus, which may reflect generalized bodily flexion associated with a preparatory behavioral response.

Acoustic Stimulation↗
PubMed2004

Responsiveness of the H reflex to loading and posture in patients following stroke.

The objective of the research was to examine the effects of loading and posture on motoneuronal excitability of the triceps surae (TS) for patients with hemiplegia. Twelve healthy subjects and 12 patient subjects with post-stroke hemiparesis (onset period: 3-60 months) were enrolled in this study. The subjects were instructed to remain in quiet sitting with the test knee straight and three standing conditions of different superincumbent loads by shifting body weight to the test leg (10%, 50%, and 90% of body weight), while the H reflexes and M waves of the TS were measured. The results clearly indicated that H reflex amplitudes were not affected by different loading conditions in standing for both healthy subjects and patients who had a previous stroke. In addition, the H reflex amplitude in quiet standing for healthy subjects was significantly downward modulated relative to that in relaxed sitting with the test knee straight, but this posturally driven modulation was impaired in patients following stroke. Current electrophysiological findings imply that body weight as a means for rehabilitation facilitation had little immediate effect on paretic TS, and absence in postural gating of reflex excitability appeared to be an incentive for postural instability resulting from post-stroke hemiparesis.

Adult↗
PubMed2005

The short-term reliability of grip strength measurement and the effects of posture and grip span.

PURPOSE: Because of the difficulty in verifying the reliability and validity of grip strength there is still no consensus regarding its measurement, particularly short-term reliability. The present study was conducted to investigate the short-term reliability of grip strength measurement and the effects of posture and grip span. METHODS: One hundred healthy subjects (50 men, 50 women; mean age, 38.2 y; range, 22-58 y) were evaluated. Grip strength was measured twice as a single set by using a dynamometer and the mean value for each hand was recorded. First 3 sets of measurements were performed using 2 different approaches: (1) continuous measurement without rest and (2) interval measurement with a 1-minute rest after each set. Next 1 set of measurements was performed with 3 types of grip span: standard grip span (which was measured as one half the distance between the index finger tip and the metacarpophalangeal joint flexion crease at the base of the thumb), +10% of the standard grip span, and -10% of the standard grip span. Finally 1 set of measurements was performed in 3 postures: standing, sitting, and supine. RESULTS: During continuous measurement the grip strength decreased gradually as the number of sets increased. During interval measurement, however, there was no change among sets for both genders and each hand. On the basis of this result subsequent studies were performed using interval measurement. There was no significant difference in maximum grip strength between the standard and +10% of standard grip span measurements; however, the -10% of standard model gave the minimum grip strength in both genders. With regard to posture the minimum grip strength in both genders was obtained when the subject was supine, with no difference between standing and sitting. CONCLUSIONS: Our study showed that interval measurement with a 1-minute rest after each set yielded a constant value; therefore, we advocate this approach for rapid evaluation of grip strength under different conditions. In addition the influence of grip span and posture should be considered to maximize data accuracy.

Adult↗
PubMed2004

Whole-body vibration and postural stress among operators of construction equipment: a literature review.

INTRODUCTION: Operators of construction equipment perform various duties at work that expose them to a variety of risk factors that may lead to health problems. A few of the health hazards among operators of construction equipment are: (a) whole-body vibration, (b) awkward postural requirements (including static sitting), (c) dust, (d) noise, (e) temperature extremes, and (f) shift work. It has been suggested that operating engineers (OEs) are exposed to two important risk factors for the development of musculoskeletal disorders: whole-body vibration and non-neutral body postures. METHOD: This review evaluates selected papers that have studied exposure to whole-body vibration and awkward posture among operators of mobile equipment. There have been only few studies that have specifically examined exposure of these risk factors among operators of construction equipment. Thus other studies from related industry and equipment were reviewed as applicable. CONCLUSION: In order to better understand whole-body vibration and postural stress among OEs, it is recommended that future studies are needed in evaluating these risk factors among OEs.

Equipment and Supplies↗