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PubMed1987

Behavioral and postural changes observed with use of adaptive seating by clients with multiple handicaps.

Adaptive seating devices (ASDs) are used in the treatment of children with multiple handicaps. This longitudinal study evaluated, through direct observation and parent-guardian assessment, the behavioral changes seen with the use of ASDs and programming. Nineteen individuals with multiple handicaps and developmental disabilities, aged 1 to 6 years, participated as subjects. Data were collected by a trained observer from eight on-site evaluations and from parent-guardian responses to a preequipment and postequipment questionnaire. Evaluations were made every six weeks, starting about three months before and ending about six months after receiving the seating devices. The activities observed were head control, controlled sitting posture, visual tracking, reach, and grasp. Rating scale data were analyzed using an analysis of variance and a Friedman's test. Other data were analyzed descriptively for frequencies and central tendencies. Sitting posture, head control, and grasp improved significantly. Parent perceptions of the equipment indicated that the chairs freed parents from the need to provide support for their children's activities of daily living, which enabled them to participate in other activities with the children and around the home.

Adolescent↗
PubMed1990

Posture, place, and mood effects on ambulatory blood pressure.

Ambulatory blood pressure was studied as a function of posture, place, and mood in 131 subjects classified according to race, gender, and hypertensive status. The effect of posture was significant and explained a substantial proportion of within-subject variability. After controlling for posture, significant place and mood effects were observed when subjects were sitting but not when they were standing. Home vs. work differences in both systolic and diastolic blood pressure were significantly greater in Whites than in Blacks. Similar differences in systolic blood pressure were greater in mild hypertensive than in normotensive subjects. The results of this study underscore the need to control for effects of posture when interpreting ambulatory blood pressure readings.

Adult↗
PubMed1995

An optimal control model for analyzing human postural balance.

The question posed in this study is whether optimal control and state estimation can explain selection of control strategies used by humans, in response to small perturbations to stable upright balance. To answer this question, a human sensorimotor control model, compatible with previous work by others, was assembled. This model incorporates linearized equations and full-state feedback with provision for state estimation. A form of gain-scheduling is employed to account for nonlinearities caused by control and biomechanical constraints. By decoupling the mechanics and transforming the controls into the space of experimentally observed strategies, the model is made amenable to the study of a number of possible control objectives. The objectives studied include cost functions on the state deviations, so as to control the center of mass, provide a stable platform for the head, or maintain upright stance, along with a cost function on control effort. Also studied was the effect of time delay on the stability of controls produced using various control strategies. An objective function weighting excursion of the center of mass and deviations from the upright stable position, while taking advantage of fast modes of the system, as dictated by inertial parameters and musculoskeletal geometry, produces a control that reasonably matches experimental data. Given estimates of sensor performance, the model is also suited for prediction of uncertainty in the response.

Biomechanical Phenomena↗
PubMed1999

EMG responses in lower leg muscles elicited by head-taps.

Forehead-taps elicited short-latency motor responses in the lower leg muscle which, together with vestibulocollic reflexes, might contribute to multisensory control of posture. We tested this paradigm in human subjects standing upright in order to determine if the responses differed depending on whether the taps were to the forehead or temporal bone. Forehead-taps elicited short-latency inhibitory EMG responses in both gastrocnemius muscles with a mean latency of 48 to 99 ms. The right or left temporal bone-taps elicited short-latency inhibitory EMG responses in the ipsilateral gastrocnemius muscle of 47 to 77 ms, short-latency excitatory EMG responses in the contralateral gastrocnemius muscle of 46 to 78 ms, and short-latency excitatory EMG responses in the contralateral tibialis anterior muscle of 48 to 78 ms. The temporal bone-taps elicited short-latency inhibitory EMG responses in the ipsilateral gastrocnemius muscle and excitatory EMG responses in the contralateral gastrocnemius muscle, which were thought to be generated by vestibular afferents and convergent with vestibular input for the multisensory control of posture.

Adult↗
PubMed1992

Self-sitting and reaching in 5- to 8-month-old infants: the impact of posture and its development on early eye-hand coordination.

The relation between progress in the control of posture (i.e., the achievement of self-sitting posture) and the developmental transition from two-handed to one-handed engagement in infant reaching was investigated. Two groups of 5- to 8-month-old infants, who were either able or yet unable to sit on their own, were videotaped while they reached for objects in four different posture conditions that provided varying amounts of body support. Videotapes of infant reaches were microanalyzed to determine the relative engagement of both hands during reaches. Results demonstrate the interaction between postural development and the morphology of infant reaching. Nonsitting infants displayed symmetrical and synergistic engagement of both arms and hands while reaching in all but the seated posture condition. Sitting infants, by contrast, showed asymmetrical and lateralized (one-handed) reaches in all posture conditions. Results also show that, aside from posture, the perceived spatial arrangement of the object display is a determinant of infant reaching. Combined, these results are discussed as evidence for the interaction between postural and perceptual development in the control of early eye-hand coordination.

Journal Article↗
PubMed2001

Effects of head immobilization on the coordination and control of head and body reorientation and translation during steering.

Changing the direction of locomotion involves lateral translation of the body in addition to body reorientation to align with the new travel direction. We designed this study to investigate the CNS control of these postural adjustments. The specific aims of the study were: first, to test the hypothesis that anticipatory head movements towards the new travel path are proactively controlled by the CNS to provide a stable frame of reference for body reorientation and, second, to investigate the relative contribution of foot placement and other mechanisms to the control of lateral body translation during steering. We achieved these aims by carrying out a comprehensive biomechanical analysis of participants performing a steering paradigm and observing the effects of immobilizing the head (by fixing it to the trunk) on postural control and the sequencing of body segment reorientation. Participants performed a task whereby they were visually cued to change their direction of walking by 30 degrees or 60 degrees, left or right, at the midpoint of a 9-m path. The temporal sequence of body reorientation was consistent with previous findings that the head starts to turn in the direction of travel before the rest of the body. Translation of the centre of mass (COM) in the new travel direction was achieved both through alternate placement of the contralateral foot prior to the turn step and use of a hip strategy to control the body pendulum during swing. Immobilizing the head resulted in the following significant changes: earlier onset of trunk yaw with respect to cue delivery, later trunk roll onset and a reduction in trunk roll amplitude. These results provide valuable information regarding the biomechanics of steering and support the hypothesis that aligning the head with motor or locomotor goals using vision provides the CNS with a stable frame of reference, independent of gaze, that can be used to control the repositioning of the body in space.

Adult↗
PubMed1993

Effect of posture and acute glycaemic control on the excretion of retinol-binding protein in normoalbuminuric insulin-dependent diabetic patients.

1. It has been suggested that tubular damage may precede glomerular damage at the onset of diabetic nephropathy. This may be reflected by increased urinary excretion of low-molecular-mass proteins, such as retinol-binding protein. 2. We have measured the urinary excretion rate of retinol-binding protein overnight, during orthostasis and during a hyperinsulinaemic euglycaemic clamp (blood glucose concentration 7.0 mmol/l) with stable diuresis in 34 normotensive, normoalbuminuric insulin-dependent diabetic patients and in 10 normal control subjects. Normal control subjects were not clamped. A further four normoalbuminuric insulin-dependent diabetic patients were rendered euglycaemic without a water load. 3. Overnight retinol-binding protein excretion rate was 58 (16-157) [median(range)] ng/min in patients with insulin-dependent diabetes and 32 (15-72) ng/min in control subjects (P < 0.01). The excretion rate did not change during orthostasis [patients with insulin-dependent diabetes, 67 (3-173) ng/min; control subjects, 23 (5-78) ng/min]. During the euglycaemic clamp retinol-binding protein excretion rate increased to 383 (78-4897) ng/min in patients with insulin-dependent diabetes (P < 0.01). An average increment in retinol-binding protein excretion rate of greater than 4000% was noted after acute euglycaemia in those patients with insulin-dependent diabetes who were not water-loaded. 4. In insulin-dependent diabetes, both overnight and orthostatic retinal-binding protein excretion was not correlated with fasting blood glucose concentration, HbA1, fructosamine or duration of diabetes. The absolute and incremental excretion rates of retinol-binding protein during the clamp were, however, correlated with both fasting blood glucose concentration and glucose excretion rate (rs = 0.41-0.48, P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1987

Neural control of a cyclic postural behavior in the crayfish, Procambarus clarkii: the pattern-initiating interneurons.

As part of its repertoire of defensive behaviors, the crayfish, Procambarus clarkii, may respond to mildly threatening tactile or visual stimuli from the front of its body by walking backwards. During this behavior, the abdomen undergoes complex cyclical movements involving flexion and extension of the postural musculature which cause the tail to alternately contact and withdraw from the substrate. Intracellular neuropil recordings and dye injections were used to search for the interneurons responsible for initiating this postural motor pattern in the crayfish abdomen. Several diverse morphological types of interganglionic pattern-initiating (PI) interneurons were found. Each interneuron, when driven intracellularly, was capable of eliciting the same motor program, in its entirety, throughout the abdominal nerve cord. During pattern generation, PI interneurons exhibited a burst of spikes preceding the motor output. Silencing single PI interneurons with hyperpolarizing current during pattern generation failed to affect the motor program, indicating a redundancy of pattern-initiating function. The observations of extensive dye-coupling with other parallel axons, consistent dye-coupling with other identified cells in the pattern-initiating system, and the presence of multiple spike amplitudes in the bursts suggested electrotonic coupling among the PI interneurons. An additional group of interganglionic interneurons, the partial pattern-initiating (PPI) interneurons, were found to comprise a significant subset of the pattern-initiating system. As with the PI cells, the PPI interneurons exhibited a complex burst of spikes just preceding the patterned motor program. However, the PPI interneurons were only capable of eliciting an incomplete, though recognizable, postural motor pattern. Silencing any PPI interneuron during pattern generation caused a deficit in the motor pattern, indicating either an absence or lesser degree of functional redundancy within the PPI interneuron population compared to that occurring within the PI interneuron group. We conclude that a large number of PI interneurons are presynaptic to a relatively small group of PPI interneurons which, in turn, conduct pattern-initiating signals to the ganglionic oscillators. Our results indicate that pattern-initiation is accomplished through a command system involving multiple command elements organized in a coordinated interganglionic network.

Animals↗
PubMed2000

Cardiovascular responses to upright and supine exercise in humans after 6 weeks of head-down tilt (-6 degrees).

Seven healthy men performed steady-state dynamic leg exercise at 50 W in supine and upright postures, before (control) and repeatedly after 42 days of strict head-down tilt (HDT) (-6 degrees) bedrest. Steady-state heart rate (fc), mean arterial blood pressure, cardiac output (Qc), and stroke volume (SV) were recorded. The following data changed significantly from control values. The fc was elevated in both postures at least until 12 days, but not at 32 days after bedrest. Immediately after HDT, SV and Qc were decreased by 25 (SEM 3)% and 19 (SEM 3)% in supine, and by 33 (SEM 5)% and 20 (SEM 3)% in upright postures, respectively. Within 2 days there was a partial recovery of SV in the upright but not in the supine posture. The SV and Qc during supine exercise remained significantly decreased for at least a month. Submaximal oxygen uptake did not change after HDT. We concluded that the cardiovascular response to exercise after prolonged bedrest was impaired for so long that it suggested that structural cardiac changes had developed during the HDT period.

Bed Rest↗
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↗
PubMed1998

Control of upright standing posture during low-frequency linear oscillation.

We examined the effects of anteroposterior movement of a sled on human upright standing. Each of six healthy men stood on the platform of a sled in the dark. The sinusoidal acceleration was provided, from 0.02 to 0.04 G, followed by 0.06 and 0.08 G, at a stroke length from 6 to 10 m and then to 14 m. Low acceleration (0.02 and 0.04 G) induced body sway, pivoting on the ankle joint. High acceleration (0.06 and 0.08 G) increased body sway, but the head-neck joint remained locked upright. The electromyographic recordings of the lower leg muscles revealed continuous tonic EMG activities of the gastrocnemius and tibialis anterior muscles at acceleration of 0.02 and 0.04 G, while reciprocal activation was observed at 0.06 and 0.08 G. During head movement, the neck muscles were slightly activated tonically at acceleration of 0.02 and 0.04 G, but they were markedly and tonically activated at 0.06 and 0.08 G. We speculate that the sled oscillation caused body sway in proportion to the acceleration, with the ankle joint playing a principal role. Analysis of neck movement also revealed that the head was held in a fixed upright position, indicating that the vestibulocollic reflex might tonically activate the neck muscles.

Acceleration↗
PubMed1990

Central effects of the angiotensin-converting enzyme inhibitor, captopril. II. Electroencephalogram and body sway.

1. Effects of single doses of captopril (12.5, 25 and 50 mg) on the electroencephalogram (EEG) and on body sway were studied in fourteen healthy male subjects. Oxazepam (15 mg), as an active control, and two placebos were included in the study, together with a single dose of atenolol (100 mg). Medication was administered double-blind at 11.00 h, and assessments made before and at 2 and 4 h after drug ingestion. 2. There were no changes in the EEG with captopril. Oxazepam reduced the circadian rise in alpha activity, while atenolol decreased beta power. Delta activity was modified by both oxazepam and atenolol. 3. A reduction in lower frequencies of body sway (0.05-1 Hz) occurred with captopril, while the spectra were unaffected by oxazepam. Atenolol increased (P less than 0.05) activity in the frequency range 0.75-2.75 Hz. 4. These observations suggest that captopril is free of central effects such as sedation that may occur with beta-adrenoceptor antagonists. Reduced body sway with captopril could reflect improved integration of central and peripheral control of posture.

Atenolol↗
PubMed2004

Control of human mandibular posture during locomotion.

Mandibular movements and masseter muscle activity were measured in humans during hopping, walking and running to determine whether reflexes contribute to the maintenance of jaw position during locomotion. In initial experiments, subjects hopped so that they landed either on their toes or on their heel. Landing on the toes provoked only small mandibular movements and no reflex responses in the masseter electromyogram (EMG). Landing on the heels with the jaw muscles relaxed caused the mandible to move vertically downwards relative to the maxilla, and evoked a brisk reflex response in the masseter at monosynaptic latency. Neither this relative movement of the mandible nor the reflex was seen when the teeth were clenched: hence the reflex is not the result of vestibular activation during head movement. The same variables were measured in a second series of experiments while subjects stood, walked and ran at various speeds and at various inclinations on a treadmill. During walking, the vertical movements of the head and therefore the mandible were slow and small, and there was no tonic masseter EMG or gait-related activity in the jaw-closing muscles. When subjects ran, the vertical head and jaw movement depended on the running speed and the inclination of the treadmill. Landing on the heels induced larger movements than landing on the toes. About 10 ms after each foot-strike, the mandible moved downwards relative to the maxilla, thereby stretching the jaw-closing muscles and activating them at segmental reflex latency. This caused the mandible to move back upwards. The strength of the reflex response was related to the speed and amplitude of the vertical jaw movement following landing. It is concluded that, during walking, the small, slow movements of the mandible relative to the maxilla are subthreshold for stretch reflexes in the jaw muscles: i.e. the mandible is supported by visco-elasticity of the soft tissues in the masticatory system. However, the brisker downward movements of the mandible after heel-landing during hopping and running evoke segmental reflex responses which contribute to the active maintenance of the posture of the mandible. This is a unique demonstration of how a stretch reflex operates to maintain posture under entirely natural conditions.

Adolescent↗