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Biomedical subjects

A S Aruin

Publications and source records attributed to A S Aruin.

At least 19 recordsLinked to original sources
PubMed2001

The role of action in postural preparation for loading and unloading in standing subjects.

The main purpose of the present study has been to find an answer to the question: Can the subject generate anticipatory postural adjustments (APAs) when a predictable postural perturbation occurs in the absence of a voluntary action? Answering this question would allow us to distinguish between two competing hypotheses on the relation between APAs and voluntary movements. One hypothesis considers both APAsigma and voluntary "focal" movements different peripheral patterns associated with a single control process, while the alternative hypothesis considers them outcomes of two parallel control processes. Healthy subjects performed series of loading and unloading trials that included: (1) catching a falling load onto another load held in extended hands; (2) catching a falling load onto a tray attached to the trunk; (3) allowing a falling load to hit another load out of the extended hands, causing an unloading; and (4) releasing a load held in extended hands by a voluntary shoulder movement. In series 1, precautions were taken to avoid possible small hand movements prior to the impact of the falling load. Available visual information on the trajectory of the falling load was manipulated. In all conditions, except when the subject's eyes were closed, APAs were seen with patterns that were adequate for counteracting expected perturbations. Quantitative electromyographic indices of APAs depended on the availability of visual information and particular methods of introducing postural perturbations despite the fact that the magnitude of the perturbation was always the same. Our findings support a hypothesis that control processes resulting in APAs can be different from control processes associated with focal voluntary movements.

Adult↗
PubMed2001

Anticipatory postural adjustments associated with lateral and rotational perturbations during standing.

We studied the role of different leg and trunk muscle groups in the generation of anticipatory postural adjustments (APAs) prior to lateral and rotational perturbations associated with predictable and self-triggered postural perturbations during standing. Postural perturbations were induced by a variety of manipulations including catching and releasing a load with the right hand extended either in front of the body or to the right side, performing bilateral fast shoulder movements in different directions, and applying brief force pulses with a hand against the wall. Perturbations in a frontal plane ("lateral perturbations") were associated with significant asymmetries in APAs seen in the right and left distal (soleus and tibialis anterior) muscles; these asymmetries dependent on the direction of the perturbation. Rotational perturbations about the vertical axis of the body generated by fast movements of the two shoulders in the opposite directions were also associated with direction-dependent asymmetries in the APAs in soleus muscles. However, rotational perturbations generated by an off-body-midline force pulse application were accompanied by direction-dependent asymmetries in proximal muscle groups, but not in the distal muscles. We conclude that muscles controlling the ankle joint play an important role in the compensation of lateral and rotational perturbations. The abundance of muscles participating in maintaining vertical posture allows the control system to use different task-dependent strategies during the generation of APAs in anticipation of rotational perturbation.

Adult↗
PubMed2001

Simple lower extremity two-joint synergy.

The purpose of this study was to describe the existence of a simple synergy in the lower extremity. Subjects performed discrete knee flexion or extension movements or ankle plantar or dorsiflexion movements in a sagittal plane, moving one of the joints "as fast as possible." Joint angles and electromyographic (EMG) signals from the biceps femoris, rectus femoris, soleus, and tibialis anterior were recorded. Typically, EMG patterns in both muscle pairs acting at the joints demonstrated the "triphasic" pattern. The knee flexor (biceps femoris) and ankle plantar flexor (soleus) tended to show simultaneous EMG bursts, while the knee extensor (rectus femoris) and ankle dorsiflexor (tibialis anterior) had similar patterns of activation. A two-joint simple synergy previously established for upper extremities seems pertinent for lower extremities as well. Such a synergy is used by the central nervous system to simplify control of the postural component of a motor task.

Adult↗
PubMed2000

Knee position feedback: its effect on management of pelvic instability in a stroke patient.

PURPOSE: This is a case study of improvement in pelvic instability due to a stroke, with treatment. The patient had narrow knee-to-knee distance due to weakness in the pelvic muscles resulting in a narrow base of support. METHOD: Treatment was focused on pre-gait activities to improve upright posture control followed by gait training involving extrinsic auditory feedback about knee-to-knee distance. RESULTS: After two weeks of therapy with feedback technique incorporated in a functional context of gait therapy, the patient was able to advance his left lower extremity with proper foot placement. Laboratory measurements showed that step width and stride length gotten better after treatment as well. CONCLUSION: An inclusion of feedback information about knee-to-knee distance could benefit gait training of patients with pelvic instability.

Aged↗
PubMed2000

The effect of shoe lifts on static and dynamic postural control in individuals with hemiparesis.

OBJECTIVE: To determine the effect of lifts to the shoe of the nonaffected leg on weight symmetry and dynamic posturography in individuals with hemiparesis. DESIGN: Quantitative posturography was performed to determine subjects' response to sudden perturbations. Subjects received graded forward and backward perturbations while standing on a movable force platform. Compelled shift of the body weight was induced with sized lifts to the shoe of the nonaffected leg. Balance responses were analyzed in terms of latency and strength of neuromuscular response. Symmetry scores were used to characterize the symmetry of stance. SETTING: Free-standing acute inpatient rehabilitation hospital. PARTICIPANTS: Ten individuals with hemiparesis as a result of unilateral stroke. MAIN OUTCOME MEASURES: Weight symmetry scores, latencies of each leg's active response to the support surface translations, and response strength scores of each leg to the platform translations. RESULTS: When no lift was used, weight symmetry was characterized by underloading of the affected limb, as well as by longer onset latencies for the affected limb compared with the stronger one (158.5 +/- 3.9 vs 151.1 +/- 3.5 ms; p < .01 for large backward translations; 165.7 +/- 7.2 vs 158.0 +/- 5.1 ms; p < .01 for large forward translations). Response strength of the nonparetic limb was 2 times greater than the response strength of the weaker extremity (p < .05). Compelled weight shift induced by lifts applied to the shoe of the nonparetic limb promoted improved weight symmetry, shortened latencies, and increased magnitudes of the response strength. CONCLUSION: Lifts applied to the shoe of the stronger limb induced a body weight shift toward the paretic limb and resulted in improved symmetry of stance and postural control of individuals with hemiparesis. We suggest that compelled weight distribution induced by lifts to the shoe of the stronger limb could help treat ambulatory individuals with asymmetric stance and hemiparesis caused by unilateral stroke.

Adult↗
PubMed1998

Anticipatory postural adjustments in conditions of postural instability.

OBJECTIVES: The purpose of this study was to investigate anticipatory postural adjustments (APAs) in standing subjects who performed a standard motor action triggering a standard postural perturbation (releasing a 2.2 kg load from extended arms) in conditions of different stability requirements. METHODS: The degree of stability was varied either by balancing on special boards with long and narrow support beams or by instructions to the subjects. In the first series of experiments 13 subjects stood on the board facing either perpendicular to the beam (instability in a sagittal plane) or along the beam (instability in frontal plane); different widths of the beam were used to vary the degree of instability. During the second series of experiments (6 subjects) inclined and one-legged postures were used to induce instability in sagittal and frontal planes respectively. EMG activity of rectus abdominis, erector spinae, rectus femoris, biceps femoris, tibialis anterior, and soleus muscles were recorded. Statistical methods included repeated measures analysis of variance (ANOVA) with direction of instability and level of instability being major factors, descriptive statistics, and post hoc Student's t tests. RESULTS: The integral measure of changes in the background electromyographic activity of postural muscles during APAs depended on two factors related to the postural task: (1) standing on a platform with a narrow support area led to an attenuation of the APAs; and (2) these effects were stronger when instability was in a sagittal rather than in the frontal plane. The anticipatory component in the displacement of the center of pressure did not show a clear attenuation that would depend on the direction of instability. CONCLUSIONS: We suggest a hypothesis that, in conditions of high stability demands, the central nervous system may suppress APAs as a protection against their possible destabilizing effects. These effects are more pronounced when the direction of an expected perturbation is in the plane of instability.

Adult↗
PubMed1997

Anticipatory postural adjustments during standing in below-the-knee amputees.

OBJECTIVE: We studied the role of adaptive changes within the central nervous system in anticipatory postural adjustments seen in unilateral below-the-knee amputees. DESIGN: Changes in electromyographic and mechanical variables were compared during standardized tasks performed by standing subjects. BACKGROUND: Anticipatory postural adjustments represent an important mechanism of postural control which was expected to be changed in amputees because of both mechanical and secondary, neurological reasons. METHODS: Six patients after a below-the-knee amputation and six control subjects stood on a force platform and performed fast bilateral shoulder movements and also dropped or caught a load from (into) extended hands. Anticipatory changes in the background activity of postural muscles were analysed. RESULTS: In amputees, there were cases of marked asymmetry in anticipatory changes of the background muscle activity which were larger on the intact side of the body but were commonly small or absent on the side of the amputation. This asymmetry could lead to larger mediolateral forces and displacements of the centre of pressure. CONCLUSIONS: We suggest that asymmetrical patterns of anticipatory postural adjustments reflect central adaptive changes secondary to the amputation. Rehabilitation approaches would benefit from understanding and taking advantage of the adaptive changes within the central nervous system. RELEVANCE: We demonstrated asymmetries in patterns of anticipatory postural adjustments during voluntary arm movements and load manipulations by standing unilateral amputees. This finding is of potential importance for rehabilitation of amputees and their prosthetic training.

Journal Article↗
PubMed1996

Are there deficits in anticipatory postural adjustments in Parkinson's disease?

We studied anticipatory postural adjustments in patients with Parkinson's disease who dropped a load from extended arms while standing. Anticipatory postural adjustments were seen when load dropping was induced by a fast, bilateral shoulder abduction but not when it was induced by pressing a trigger with the right thumb. We conclude that anticipatory postural adjustments in patients with Parkinson's disease can change with the magnitude of an action which is used to trigger a predictable postural perturbation. Thus, the described deficits in anticipatory postural adjustments in patients with Parkinson's disease are likely to be of quantitative rather than qualitative nature.

Aged↗
PubMed1996

Anticipatory postural adjustments during self-initiated perturbations of different magnitude triggered by a standard motor action.

The purpose of the study was to define whether anticipatory postural adjustments scale with the magnitude of a self-triggered postural perturbation when a standard motor action triggers the perturbation. Standing subjects generated vertical forces of different magnitude with their extended arms against a bar connected through a rigid cord to the floor. They released the bar with a standard bilateral shoulder abduction. Anticipatory postural adjustments were seen as changes in the level and/or timing of the background activation of postural muscles. Muscles of the dorsal part of the legs and of the trunk demonstrated an anticipatory decrease in the level of activation, commonly leading to its complete disappearance. There was no relation between the magnitude of the unloading and the timing of the changes in the background activity of these muscles. Muscles of the frontal part of the legs and of the trunk demonstrated an anticipatory increase in their activity whose timing and amplitude correlated positively with the magnitude of the perturbation. We conclude that anticipatory postural adjustments can be scaled with respect to the magnitude of a self-triggered perturbation.

Adult↗
PubMed1996

Organization of a simple two-joint synergy in individuals with Down syndrome.

Subjects with Down syndrome and age- and gender-matched control subjects performed discrete elbow or wrist, flexion or extension movements in a sagittal plane, moving one of the joints as fast as possible. The hand was either pronated or supinated. In control subjects, alternating bursts of activity were seen in the agonist-antagonist muscle pair controlling the nonfocal joint. Subjects with Down syndrome, in most series, demonstrated simultaneous bursts of activity in the flexor and extensor muscles controlling both joints. This group difference was particularly pronounced for the muscles controlling the nonfocal joint. We assume that the central nervous system may use two strategies to avoid flapping of a postural joint. The more universal co-contraction strategy in Down syndrome may be viewed as an adaptive feature reflecting a general tendency of these persons to trade efficacy for safety.

Adult↗
PubMed1995

Directional specificity of postural muscles in feed-forward postural reactions during fast voluntary arm movements.

Healthy subjects performed bilateral fast shoulder movements in different directions while standing on a force platform. Anticipatory postural adjustments were seen as changes in the electrical activity of postural muscles as well as displacements of the center of pressure and center of gravity. Postural muscle pairs of agonist-antagonist commonly demonstrated triphasic patterns starting prior to the first electromyographic (EMG) burst in the prime-mover muscle. Proximal postural muscles demonstrated the largest anticipatory increase in the background activity during movements in one of the two opposite directions (forward or backwards). These changes progressively decreased when movements deviated from the preferred direction and frequently disappeared during movements in the opposite direction. The patterns in distal muscles varied across subjects and could demonstrate larger anticipatory changes during movements forward and backwards as compared to movements in intermediate directions. Bilateral addition of inertial loads to the wrists did not change the general anticipatory patterns, while making some of their features more pronounced. Anticipatory postural adjustments were followed by later changes in the activity of postural muscles, also reflected in the mechanical variables. Changes in leg joint angles revealed a "hip-ankle strategy" during shoulder flexions and an "ankle strategy" during shoulder extensions. The study demonstrates different behaviors of proximal and distal muscles during anticipatory postural adjustments in preparation for fast arm movements. We suggest that the proximal muscles produce a general pattern of postural adjustments, while distal muscles take care of fine adjustments that are more likely to vary across subjects.

Adult↗
PubMed1995

The role of motor action in anticipatory postural adjustments studied with self-induced and externally triggered perturbations.

This study investigated the relation between the magnitude of a motor action triggering a postural perturbation and the magnitude of anticipatory postural adjustments. Subjects stood on a force platform and held, in extended arms, a balloon with a 2.2-kg load suspended on a rigid cord. In different series, unloadings were induced by fast bilateral shoulder abduction movements, by popping the balloon with a tack taped to the subject's right middle finger, or by the experimenter popping the balloon. Anticipatory postural adjustments were seen during all self-initiated unloadings as changes in the level of activation of postural muscles and in displacements of the center of pressure. However, absolute values of these changes were significantly smaller in the series with balloon popping as compared to the series with shoulder abductions. Such reactions were absent when the unloading was triggered by the experimenter. We conclude that a self-triggered perturbation is always associated with anticipatory postural adjustments, while the magnitude of the adjustments may be scaled with respect to the magnitude of a motor action used to induce the perturbation.

Adult↗
PubMed1995

Feedforward postural adjustments in a simple two-joint synergy in patients with Parkinson's disease.

Patients with Parkinson's disease, age-matched controls and young control subjects performed discrete elbow or wrist movements in a sagittal plane under the instruction to move one of the joints "as fast as possible." Relative stability of the other, postural joint was comparable in all 3 groups, while movement time was the highest in the patients and the lowest in young controls. Typically, EMG patterns in both muscle pairs acting at the joints demonstrated a commonly observed "tri-phasic" pattern. A cross-correlation analysis of the EMGs confirmed virtually simultaneous bursts in the wrist and elbow flexors and in the wrist and elbow extensors. In all 3 groups, there were no signs of anticipatory activation of postural muscles in about 90% of movements. We consider postural anticipation not a separate process, but a separate peripheral pattern of a single control process that may involve a number of joints and muscles. We conclude that the postural deficits in Parkinson's disease are not related to a basic deficit in the ability to generate feedforward postural adjustments but to other factors that may include the specificity of maintaining the vertical posture in the field of gravity.

Aged↗
PubMed1995

Anticipatory postural adjustments during self inflicted and predictable perturbations in Parkinson's disease.

This study investigated the relation between impaired anticipatory postural adjustments and bradykinesia in Parkinson's disease. Patients with Parkinson's disease and age matched controls stood on a platform. In one series of experiments, they performed fast, discrete shoulder flexion or extension movements. In another series, they were required to press a trigger with the right thumb and thus to release a load that was suspended from a bar which they were holding in front of them in extended arms. One more series included catching a load on the same bar. Anticipatory changes in the activity of postural muscles before fast voluntary movements occurred in patients and controls although the patients showed higher variability of anticipatory patterns. During load dropping and catching, control subjects had reproducible, although smaller, anticipatory changes in postural muscle activity. Such changes were absent in all but one patient. Two sources of these postural perturbations were analysed. The anticipatory postural adjustments in different muscle groups may counteract perturbations of different origin. The distal to proximal sequencing of joint involvement in postural reactions may be related to different reference points and working points associated with these tasks compared with reaching limb movements. The deficit in anticipatory postural adjustments in Parkinson's disease is likely to be unrelated to bradykinesia and is more likely to reflect the deficits in the basic processes of preparation and initiation of a motor act.

Aged↗
PubMed1984

Biomechanical characteristics of human ankle-joint muscles.

Equivalent biomechanical characteristics of human ankle-joint muscles have been determined by impact and vibration tests. The estimate of the stiffness and damping coefficients has yielded, respectively, (2.67 +/- 0.48) X 10(4) N X m-1 and (811.58 +/- 201.3) N X s X m-1 by impact actions, n = 126; (1.49 +/- 0.35) X 10(4) N X m-1 and (430.1 +/- 36.1) N X s X m-1 -by vibration actions, n = 7. The characteristics of the ankle-joint muscles of subjects representing different kinds of sports have proved to be different.

Ankle Joint↗
PubMedDate not supplied

Compelled weightbearing in persons with hemiparesis following stroke: the effect of a lift insert and goal-directed balance exercise.

The hypotheses have been tested that 1) symmetry of weightbearing in persons who have sustained a stroke could be improved by the addition of a lift to the shoe on the non-paretic lower limb and 2) compelled weightbearing resulting from the addition of a lift in conjunction with targeted exercise helps to overcome the learned disuse of the paretic limb. Weightbearing on the paretic side was measured in eight persons with hemiparesis during quiet standing and in conditions of compelled weight shift. Compelled weight shifts were applied with special lifts to the shoe on the non-paretic limb of the subjects. An increase in symmetrical weightbearing was recorded in conditions of compelled weight shifts: 10-mm lift provided the best symmetry of bipedal standing. We suggest that improved symmetry of bipedal standing obtained with the lift of the non-paretic limb would help in overcoming the learned disuse of the affected limb. Pre- and post-test results of a person with hemiparesis who was wearing a shoe lift on the non-paretic limb during a 6-week physical therapy program showed statistically significant improvement of walking speed, stride length, and weightbearing. Such findings support the idea of using compelled weightbearing via lifting and targeted exercise during treatment.

Aged↗