Properties of postural adjustments associated with rapid arm movements

1982 ◽  
Vol 47 (2) ◽  
pp. 287-302 ◽  
Author(s):  
P. J. Cordo ◽  
L. M. Nashner
Keyword(s):  
Steady State ◽  
Stretch Reflex ◽  
Human Subjects ◽  
Reaction Times ◽  
Body Sway ◽  
Support Surface ◽  
Free Standing ◽  
Postural Adjustments ◽  
Temporal Sequencing ◽  
Postural Equilibrium

1. We have examined rapid postural adjustments associated with a class of voluntary movements that disturb postural equilibrium. In the text that follows, these motor activities are termed associated postural adjustments and voluntary focal movements, respectively. Standing human subjects performed a variety of movement tasks on a hand-held manipulandum, resulting in disturbances to their postural equilibrium. The experimental use of movements that interact with the subject's environment in a relatively simple was permitted a more precise comparison of the postural adjustments with their associated focal movements. 2. Subjects either pulled or pushed on a stiff interface (the handle) or they responded in a predetermined way to handle perturbations. These activities were carried out with various degrees of steady-state postural stability. Prior to and during these movements, support surface and handle forces, electromyographic (EMG) signals, and body sway were monitored. 3. In addition to previously shown postural adjustments associated with reaction-time armed movements, we have demonstrated these postural activities occur in concept with segmental stretch reflexes and self-initiated (untriggered) movements. Postural adjustments were initiated shortly before all focal movements tested except the short-latency component of the biceps stretch reflex (25- to 30-ms latency). However, this reflex component was rarely elicited by handle perturbations in free-standing subjects; therefore, postural adjustments usually preceded any biceps activity under this condition. 4. By varying the degree of steady-state postural equilibrium, a reciprocal gain/threshold relationship between postural and focal components was documented, i.e., when stability was high, postural activity was reduced or absent and focal activity enhanced. Conversely, the biceps stretch reflex was difficult to elicit under any condition where the subjects was not fully supported in the direction of movement and reaction times of focal movements were prolonged. 5. Postural activities associated with focal movements were found to share a number of organizational properties with automatic postural adjustments to support surface movements. Specifically, the postural muscle synergies were equivalent in muscle composition, relative activation magnitudes, and relative temporal sequencing. Furthermore, both types of postural adjustments were highly specific in locus and magnitude to the quality of steady-state postural equilibrium (e.g., postural "set"). 6. A conceptual model is proposed that suggests one simple way in which the reciprocal influence of postural set on postural and focal movement components and their temporal sequencing might be accomplished. Furthermore, we propose in this model a common central organization of postural adjustments associated with focal movements and those elicited by support-surface movements.

scholarly journals Age-Related Changes in Human Posture Control: Sensory Organization Tests

1990 ◽  
Vol 1 (1) ◽  
pp. 73-85 ◽  
Author(s):  
R.J. Peterka ◽  
F.O. Black
Keyword(s):  
Visual Cues ◽  
Human Subjects ◽  
Body Sway ◽  
Support Surface ◽  
Eyes Closed ◽  
Sensory Organization ◽  
Age Related ◽  
Eyes Open ◽  
Orientation Cues ◽  
Anterior Posterior

Postural control was measured in 214 human subjects ranging in age from 7 to 81 y. Sensory organization tests measured the magnitude of anterior-posterior body sway during six 21 s trials in which visual and somatosensory orientation cues were normal, altered (by rotating the visual surround and support surface in proportion to the subject’s sway), or vision eliminated (eyes closed). No age-related increase in postoral sway was found for subjects standing on a fixed support surface with eyes open or closed. However, age-related increases in sway were found for conditions involving altered visual or somatosensory cues. Subjects older tban about 55 y showed the largest sway increases. Subjects younger than about 15 y were also sensitive to alteration of sensory cues. On average, the older subjects were more affected by altered visual cues, whereas younger subjects had more difficulty with altered somatosensory cues.

scholarly journals Age-Related Changes in Human Posture Control: Motor Coordination Tests

1990 ◽  
Vol 1 (1) ◽  
pp. 87-96 ◽  
Author(s):  
R.J. Peterka ◽  
F.O. Black
Keyword(s):  
Motor Coordination ◽  
Center Of Pressure ◽  
Human Subjects ◽  
Body Sway ◽  
Support Surface ◽  
Age Related ◽  
Postural Responses ◽  
Surface Displacements ◽  
Normal Human ◽  
Motor Tests

Postural responses to support surface displacements were measured in 214 normal human subjects ranging in age from 7 to 81 y. Motor tests measured leg muscle electromyographic (EMG) latencies, body sway, and the amplitude and timing of changes in center of pressure displacements in response to sudden forward and backward horizontal translations of the support surface upon which the subjects stood. There were small increases in both EMG latencies and the time to reach the peak amplitude of center of pressure responses with increasing age. The amplitude of center of pressure responses showed no change with age if the amplitude measures were normalized by a factor related to subject height. In general, postoral responses to sudden translations showed minimal changes with age, and all age-related trends that were identified were small relative to the variability within the population.

scholarly journals Sensory reweighting dynamics following removal and addition of visual and proprioceptive cues

2016 ◽  
Vol 116 (2) ◽  
pp. 272-285 ◽  
Author(s):  
Lorenz Assländer ◽  
Robert J. Peterka
Keyword(s):  
Steady State ◽  
Time Course ◽  
Temporal Dynamics ◽  
Transition Period ◽  
Sensory System ◽  
Experimental Tests ◽  
Body Sway ◽  
Support Surface ◽  
Sensory Cues ◽  
Sensory Reweighting

Removing or adding sensory cues from one sensory system during standing balance causes a change in the contribution of the remaining sensory systems, a process referred to as sensory reweighting. While reweighting changes have been described in many studies under steady-state conditions, less is known about the temporal dynamics of reweighting following sudden transitions to different sensory conditions. The present study changed sensory conditions by periodically adding or removing visual (lights On/Off) or proprioceptive cues (surface sway referencing On/Off) in 12 young, healthy subjects. Evidence for changes in sensory contributions to balance was obtained by measuring the time course of medial-lateral sway responses to a constant-amplitude 0.56-Hz sinusoidal stimulus, applied as support surface tilt (proprioceptive contribution), as visual scene tilt (visual contribution), or as binaural galvanic vestibular stimulation (vestibular contribution), and by analyzing the time course of sway variability. Sine responses and variability of body sway velocity showed significant changes following transitions and were highly correlated under steady-state conditions. A dependence of steady-state responses on upcoming transitions was observed, suggesting that knowledge of impending changes can influence sensory weighting. Dynamic changes in sway in the period immediately following sensory transitions were very inhomogeneous across sway measures and in different experimental tests. In contrast to steady-state results, sway response and variability measures were not correlated with one another in the dynamic transition period. Several factors influence sway responses following addition or removal of sensory cues, partly instigated by but also obscuring the effects of reweighting dynamics.

Postural sway with earth-fixed and body-referenced finger contact in young and older adults

1999 ◽  
Vol 9 (2) ◽  
pp. 103-109
Author(s):  
Reginald L. Reginella ◽  
Mark S. Redfern ◽  
Joseph M. Furman
Keyword(s):  
Older Adults ◽  
Postural Sway ◽  
Center Of Pressure ◽  
Sensory Information ◽  
Body Sway ◽  
Support Surface ◽  
Proprioceptive Information ◽  
Postural Control System ◽  
Fixed Reference ◽  
Older Subjects

Sensory information from lightly touching a reference with the hand is known to influence postural sway in young adults. The primary aim of this study was to compare the influence of finger contact (FC) with an earth-fixed reference to the influence of FC with a body-fixed reference. A second goal of this study was to determine if FC is used differently by older adults compared to younger adults. Using a force plate, center of pressure at the feet was recorded from blindfolded young and older subjects during several conditions. Subjects either did or did not lightly touch a force-sensitive plate that was either earth-fixed or moved forward and backward in synchrony with body sway (that is, sway-referenced). In addition, support surface conditions were also varied, including a fixed floor and a sway-referenced floor using an EquitestTM. Results showed that the type of FC, floor condition, and age each had an effect on postural sway. Touching an earth-fixed plate decreased postural sway as compared to no touching, while touching a sway-referenced plate incresased sway. This influence of FC was enhanced when the floor was sway-referenced. Although older subjects swayed more than young subjects overall, no age-FC interactions occurred, indicating that FC was not utilized differently between the age groups. This study suggests that FC cannot be disregarded as erroneous, especially when proprioceptive information from the legs is distorted. Further, FC is integrated with other sensory information by the postural control system similarly in young and older persons.

Effects of galvanic mastoid stimulation in seated human subjects

2009 ◽  
Vol 106 (3) ◽  
pp. 893-903 ◽  
Author(s):  
Z. Ghanim ◽  
J. C. Lamy ◽  
A. Lackmy ◽  
V. Achache ◽  
N. Roche ◽  
...  
Keyword(s):  
Human Subjects ◽  
Normal Subjects ◽  
Standing Position ◽  
Reflex Response ◽  
Emg Activity ◽  
Free Standing ◽  
Vestibular Response ◽  
Vestibular Reflex ◽  
Tendon Jerk ◽  
Biphasic Responses

The vestibular responses evoked by transmastoid galvanic stimulation (GS) in the rectified soleus electromyogram (EMG) in freely standing human subjects disappear when seated. However, a GS-induced facilitation of the soleus monosynaptic (H and tendon jerk) reflex has been described in few experiments in subjects lying prone or seated. This study addresses the issue of whether this reflex facilitation while seated is of vestibulospinal origin. GS-induced responses in the soleus (modulation of the rectified ongoing EMG and of the monosynaptic reflexes) were compared in the same normal subjects while freely standing and sitting with back and head support. The polarity-dependent biphasic responses in the free-standing position were replaced by a non-polarity-dependent twofold facilitation while seated. The effects of GS were hardly detectable in the rectified ongoing voluntary EMG activity, weak for the H reflex, but large and constant for the tendon jerk. They were subject to habituation. Anesthesia of the skin beneath the GS electrodes markedly reduced the reflex facilitation, while a similar, although weaker, facilitation of the tendon jerk was observed when GS was replaced with purely cutaneous stimulation, a tap to the tendon of the sternomastoid muscle, or an auditory click. The stimulation polarity independence of the GS-induced reflex facilitation argues strongly against a vestibular response. However, the vestibular afferent volley, insufficient to produce a vestibular reflex response while seated, could summate with the GS-induced tactile or proprioceptive volley to produce a startle-like response responsible for the reflex facilitation.

Rolling balance board of adjustable geometry as a tool to assess balancing skill and to estimate reaction time delay

2021 ◽  
Vol 18 (176) ◽  
Author(s):  
Csenge A. Molnar ◽  
Ambrus Zelei ◽  
Tamas Insperger
Keyword(s):  
Reaction Time ◽  
Time Delay ◽  
Feedback Control ◽  
Mechanical Model ◽  
Human Subjects ◽  
Reaction Times ◽  
Physical Parameters ◽  
Stabilizing Feedback Control ◽  
Model Subject ◽  
Balance Board

The relation between balancing performance and reaction time is investigated for human subjects balancing on rolling balance board of adjustable physical parameters: adjustable rolling radius R and adjustable board elevation h . A well-defined measure of balancing performance is whether a subject can or cannot balance on balance board with a given geometry ( R , h ). The balancing ability is linked to the stabilizability of the underlying two-degree-of-freedom mechanical model subject to a delayed proportional–derivative feedback control. Although different sensory perceptions involve different reaction times at different hierarchical feedback loops, their effect is modelled as a single lumped reaction time delay. Stabilizability is investigated in terms of the time delay in the mechanical model: if the delay is larger than a critical value (critical delay), then no stabilizing feedback control exists. Series of balancing trials by 15 human subjects show that it is more difficult to balance on balance board configuration associated with smaller critical delay, than on balance boards associated with larger critical delay. Experiments verify the feature of the mechanical model that a change in the rolling radius R results in larger change in the difficulty of the task than the same change in the board elevation h does. The rolling balance board characterized by the two well-defined parameters R and h can therefore be a useful device to assess human balancing skill and to estimate the corresponding lumped reaction time delay.

Effect of mild hypoxia on ventilation during exercise

1962 ◽  
Vol 17 (2) ◽  
pp. 239-242 ◽  
Author(s):  
Thomas F. Hornbein ◽  
Albert Roos
Keyword(s):  
Steady State ◽  
Ventilatory Response ◽  
Human Subjects ◽  
Sympathetic Innervation ◽  
Mild Degree ◽  
Flow Through ◽  
Neural Discharge ◽  
Response To Exercise ◽  
Mild Hypoxia ◽  
Rest And Exercise

Hypoxia of mild degree (PaOO2 above 60 mm Hg) produces little or no ventilatory response in resting man during the steady state. To evaluate the possibility that the effectiveness of a hypoxic chemoreceptor drive might be enhanced by exercise, the ventilatory response to mild hypoxia was measured in two human subjects during rest and exercise. Though no significant increase in ventilation occurred at rest above a PaOO2 of 60 mm Hg, a decrease in PaOO2from 100 to 94 mm Hg produced a statistically significant increase in steady state ventilation during moderate exercise. In addition, temporary block of the sympathetic innervation to the carotid and aortic bodies in one subject resulted in a diminution of work hyperpnea. This suggests that increased sympathetic tone during exercise, by reducing blood flow through the chemoreceptors, might result in increased neural discharge and hence increased ventilation even though arterial POO2 is the same as at rest. Thus, activity of the chemoreceptors as modified by sympathetic control of their blood supply may be an important determinant of the ventilatory response to exercise. Since work hyperpnea is enhanced by even mild hypoxia, this ventilatory response may be sufficient to initiate respiratory acclimatization to altitudes so low that resting ventilation on acute exposure is unaffected. Submitted on July 31, 1961

Response to sudden torques about ankle in man. II. Postmyotatic reactions

1980 ◽  
Vol 43 (1) ◽  
pp. 86-101 ◽  
Author(s):  
G. L. Gottlieb ◽  
G. C. Agarwal
Keyword(s):  
Tibialis Anterior ◽  
Stretch Reflex ◽  
Reaction Times ◽  
Tonic Contraction ◽  
Triceps Surae ◽  
Afferent Pathways ◽  
Triggered Reaction ◽  
Applied Torque ◽  
Significant Difference ◽  
The Subject

1. Torques were applied to dorsiflex or plantarflex the ankle joint of normal human subjects who were instructed to react to them in various ways. Myoelectric and mechanical responses were recorded and analyzed. 2. Myoelectric responses in triceps surae or tibialis anterior with times of onset between 100 and 200 ms are conditional on the instruction to the subject and not the direction of the applied torque. These responses are termed postmyotatic responses. 3. The latency of the postmyotatic response is the same in both triceps surae and tibialis anterior. It is not dependent on the direction of the applied torque and consequently is not a "stretch reflex," but a triggered reaction. 4. When the subject is sitting relaxed and instructed to resist the applied torque, the magnitude of the postmyotatic response is highly and linearly correlated with the rate of ankle rotation produced by the disturbing torque. 5. Tonic contraction of the muscles prior to the onset of a stretching torque has only a slight effect on the magnitude of the postmyotatic response and usually reduces it. Prior tonic contraction of the antagonist also has a modest effect in reducing the response. 6. Instructing the subject to resist a torque as quickly and strongly as possible increases the magnitude of the postmyotatic response but has little effect on its linear functional relationship to the magnitude of the mechanical stimulus. 7. The postmyotatic response, although voluntary and kinesthetically triggered, is not completely equivalent to a visually triggered voluntary reaction because under experimental situations designed to measure simple reaction times and choice reaction times of the postmyotatic response, no significant difference is found between the two conditions. 8. It is suggested that the peripheral afferent pathways of the stretch reflex play a dual role in determining postmyotatic responses. First, they provide to supraspinal centers one early proprioceptive signal about limb perturbation that can trigger a previously selected mode of response. Second, they modulate that response by convergence, at the segmental level, of peripheral afferent signals with the descending command signals.

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