Destabilization of human balance control by static and dynamic head tilts

Effect of oculo-motor and gaze stability exercises on postural stability and dynamic visual acuity in healthy young adults

The purpose of this study was to investigate the effectiveness of oculo-motor exercises and gaze stability exercises on postural stability and dynamic visual acuity (DVA) in healthy young adults. Subjects were randomly divided into experimental (n=28) and control groups (n=13). The experimental group performed oculo-motor exercises and gaze stability exercise for three weeks and the control group did not. Pre and post postural stability during quiet standing, standing with active head rotation, and DVA were measured on both groups. Significant differences were found in postural stability during standing with active head rotation and DVA in the experimental group (p<0.05). No significant differences were found in postural stability or DVA in the control group. Improvements in postural stability and DVA after three weeks of oculo-motor exercises and gaze stability exercises suggest that this specific type of vestibular and ocular system exercises may be beneficial for healthy young adults.

Balance performance in head-shake computerized dynamic posturography: aging effects and test-retest reliability

BACKGROUND

The ability of the Sensory Organization Test (SOT) to detect subtle balance problems has been challenged. The Head-Shake Sensory Organization Test (HS-SOT) has been developed to improve the delineation of balance performance.

OBJECTIVE

The purposes of this study were: (1) to examine age-related differences in balance measured with the HS-SOT and (2) to establish the test-retest reliability of the HS-SOT in younger adults who were healthy and older adults who were healthy.

DESIGN

A test-retest design was used in this observational measurement study.

METHODS

Ninety-two younger adults who were healthy (mean age=28.3 years) and 73 older adults who were healthy (mean age=60.3 years) underwent the SOT and the HS-SOT. Seventy-seven of them (56 younger adults, 21 older adults) underwent the same assessments 1 to 2 weeks later.

RESULTS

The equilibrium scores in HS-SOT conditions 2 (head movements with eyes closed while standing on a firm surface) and 5 (head movements with eyes closed while standing on a sway-referenced surface) were significantly lower than those in tests without dynamic head movements added (SOT conditions 2 and 5). Older adults attained significantly lower scores in both HS-SOT conditions than their younger peers. The test-retest reliability values, reported as intraclass correlation coefficients (ICC [3,2]), of the HS-SOT scores in conditions 2 and 5 for the younger adults were .85 and .78, respectively; those for the older adults were .64 and .55, respectively. The corresponding minimal detectable change values for the former were 2.7 and 16.2, and those for the latter were 3.6 and 22.7.

LIMITATIONS

Only head rotation movements on the horizontal plane were tested.

CONCLUSIONS

Adding head movements to the SOT increased the separation of younger adults who were healthy and older adults who were healthy. The HS-SOT has good reliability, and the reported minimal detectable change values may facilitate the interpretation of clinical studies in which the HS-SOT is used to assess changes in balance performance in younger and older adults.

Effect of vision, proprioception, and the position of the vestibular organ on postural sway

CONCLUSION

When measured together, it seems that vision and proprioception as well as position of the vestibular organ affect postural sway, vision the most. Mediolateral (ML) sway does not seem to be influenced by the position of the vestibular organ.

OBJECTIVE

To investigate how postural sway was affected by provocation of vision, by the position of the vestibular organ, and by provocation of proprioception, when measured together.

METHODS

Postural sway was measured by using a force plate. Tests were performed with eyes open and eyes closed, with head in neutral position and rotated to the right and to the left and with head maximally extended, both standing on firm surface and on foam. Measures of ML speed (mm/s), anteriorposterior (AP) speed (mm/s), and sway area (SA) (mm(2)/s) were analyzed using a multilevel approach.

RESULTS

The multilevel analysis revealed how postural sway was significantly affected by closed eyes and standing on foam, and by the position of the vestibular organ. Closed eyes and standing on foam both significantly prolonged the dependent measurement, irrespective of whether it was ML, AP or SA. However, only AP and SA were significantly affected by vestibular position, i.e. maximal head movement to the right and extension of the head.

Efficacy of a computerized sensor system for evaluation and training of dizzy patients

Patients with vestibular hypofunction often experience dizziness and unsteadiness while moving their heads. Appropriate sensors can effectively detect a patient’s dynamic visual acuity and associated body balance control. Forty-one vestibular-deficit patients and 10 normal individuals were invited to participate in this study. Questionnaires, clinical assessment scales and objective measures were evaluated on participants’ first visits. After 12 sessions of training, all scales were evaluated again on vestibular-deficit patients. The computerized system was composed of sensors, including a gyro and strain gauges, data acquisition accessories and LabVIEW software. Results revealed that the system could effectively distinguish normal subjects from subjects with vestibular deficits. In addition, after a rehabilitation program, subjects’ subjective and objective performances were significantly improved. Based on our results, we concluded that the present system, which uses a gyro and strain gauges, may provide an effective method for assessing and treating vestibular-deficit patients.

Modified head shake computerized dynamic posturography

PURPOSE

Recent research on head shake posturography has demonstrated a modest increase in sensitivity to identifying peripheral vestibular system asymmetry when horizontal head movements were added to portions of the standard Sensory Organization Test (SOT) battery. However, limitations with respect to the head shake protocol were outlined, and usable data for assessing performance could not be established. The purpose of this study was to test a change in protocol for use of head shake SOT to address the noted limitations.

METHOD

Forty participants ranging in age from 20 to 79 years with no history of dizziness completed Conditions 2 and 5 of the SOT portion of computerized dynamic posturography on EquiTest equipment, while maintaining head still as well as 4 horizontal head movement velocity tasks.

RESULTS

Slope of a linear regression fit to 6 performance points was used to characterize each participant. Spearman's ranked correlation (r) indicated a significant relationship between the slope of the line representing a decline in performance with age (r = -.52, p = .0006).

CONCLUSIONS

The head shake modification showed a trend in increasing the separation of normal individuals across age and eliminated the limitations addressed in earlier research. Future research will investigate the head shake modification for identifying vestibular peripheral system asymmetries.

Unconstrained shoulder joint position sense does not change with body orientation

Our knowledge of the role of muscle activation on proprioception is incomplete. Previous work has either focused on comparing active and passive motions or manipulated both muscle activation and joint angles simultaneously. We conducted an experiment at the shoulder in which subjects' trunks were tilted backwards to decouple joint angle from joint torque. Twenty three healthy subjects underwent testing in an unconstrained joint position sense task. Kinematics were measured with a magnetic tracking device. The joint position sense task consisted of subjects moving their arms to a predetermined orientation in space with the help of visual feedback from the magnetic tracking device presented to the subjects through a head-mounted display. Subjects were then asked to reproduce the presented joint position in the absence of visual feedback. The protocol was performed under two tilts: upright and trunk tilted back 45 degrees. This allowed for a comparison of joint position sense at different joint angles (at the same resistive torque) and at different resistive torques (at the same joint angles). When comparing these two tilts, we found that matching based on elevation angle demonstrated no significant difference, while matching based on torques did find differences. These results implicate elevation angle at the shoulder as playing a more important role in modulating joint position sense than joint torque.

Head Shake Computerized Dynamic Posturography in Peripheral Vestibular Lesions

Purpose

To determine the sensitivity of a head shake modification to the Sensory Organization Test (SOT) of dynamic posturography in identifying (a) those patients with unilateral, peripheral vestibular hypofunction as indicated by caloric irrigation findings and (b) those patients who report that head movements provoke disruption in postural control.

Method

A prospective, single-blinded, random selection methodology was used with 91 patients stratified by the presence or absence of a significant caloric asymmetry and by the presence or absence of head movement provoked symptoms (independent variables). Postural control performance, as measured by EquiTest during the standard test and a head shake modification, served as the dependent variables.

Results

Receiver operating characteristic curves demonstrated only minor improvement in sensitivity (a) with the head shake modification for unilateral peripheral asymmetry and (b) for identification of those with complaints of head movement provoked imbalance.

Conclusions

The head shake modification to standard SOT increased the test sensitivity to identification of patients with unilateral, peripheral vestibular hypofunction and those with head movement provoked symptoms. However, this occurred with low specificity, resulting in no significant improvement in overall performance with this head shake protocol. Suggestions for further research to improve the performance of the head shake modification of SOT for clinical application are discussed.

Postural stability and vehicle kinematics during an evasive lane change manoeuvre: a driver training study

The purpose of this study was to investigate the effect of a 2-day driver-training course that emphasised postural stability maintenance during critical driving situations on postural stability and vehicle kinematics during an evasive lane change manoeuvre. Following training, the trainee group experienced enhanced postural stability during specific phases of the task. In terms of vehicle kinematics, the main adaptation to training was that trained drivers reduced the extent to which they experienced vehicle decelerations during rapid turning compared to controls. Such a strategy may confer a safety benefit due to the increased risks associated with simultaneous braking while turning during an evasive manoeuvre. The newly learned strategy was consistent with the strategy used by a group of highly skilled drivers (driving instructors). Taken together, the results of the study suggest postural stability may be a useful variable to consider in relation to the skill-based component of hierarchical driver training programmes. The findings of this study provide some preliminary evidence to suggest that postural stability may be an important consideration when instructing individuals on how to safely negotiate obstacles during driving.

The proprioceptive and agonist roles of gastrocnemius, soleus and tibialis anterior muscles in maintaining human upright posture

Humans can stand using sensory information solely from the ankle muscles. Muscle length and tension in the calf muscles (gastrocnemius and soleus) are unlikely to signal postural sways on account of balance-related modulation in agonist activity. These facts pose two questions: (1) Which ankle muscles provide the proprioceptive information? (2) Which peripheral mechanism could modulate agonist activity? To address these issues, subjects were asked to stand normally on two force plates. Ultrasound and surface EMG were recorded from the calf and tibialis anterior (TA) muscles. For all nine subjects, changes in muscle length of TA were mainly (84 +/- 9% whole trial duration) orthodoxly correlated with bodily sway (centre of gravity, CoG), i.e. in accordance with passive ankle rotation. When orthodox, TA had the highest correlation with CoG (-0.66 +/- 0.07, deep compartment, P < 0.001). For five subjects, the superficial TA compartment showed counter-intuitive changes in muscle length with CoG, probably due to the flattening of the foot and proximal attachment geometry. Gastrocnemius and soleus were usually (duration 71 +/- 23 and 81 +/- 16%, respectively) active agonists (paradoxically correlated with CoG) but, for short periods of time, they could be orthodox and then presented a moderate correlation (0.38 +/- 0.16 and 0.28 +/- 0.09, respectively) with CoG. Considering the duration and extent to which muscle length is orthodox and correlated with CoG, TA may be a better source of proprioceptive information than the active agonists (soleus and gastrocnemius). Therefore, if a peripheral feedback mechanism modulates agonist activity then reciprocal inhibition acted by TA on the calf muscles is more likely to be effective than the autogenic pathway.

Effects of dynamic head tilts on sensory organization test performance: a comparison between college-age athletes and nonathletes

STUDY DESIGN

Controlled laboratory study.

OBJECTIVE

To compare postural performance measures of athletes with those of nonathletes when completing the standard Sensory Organization Test (SOT) and a modified SOT that included dynamic head tilts (DHT-SOT).

BACKGROUND

Authors of recently published research have suggested that modifications to the SOT protocol (eg, introduction of pitch and roll head tilts) may enhance the test's sensitivity when assessing postural stability in individuals with higher balance capabilities or with well-compensated sensory deficits.

METHODS AND MEASURES

Nineteen athletes and 19 nonathletes (group) completed both the SOT and DHT-SOT (protocol). During the SOT, participants stood upright as steadily as possible for 20 seconds during each of 6 different sensory conditions. As a variation of the SOT, the DHT-SOT incorporated active pitch and roll head tilts into the SOT protocol. Four 2-way mixed-model analyses of variance (with protocol as the repeated factor) were performed to determine if the composite equilibrium score or the visual, vestibular, or somatosensory ratio scores differed between the 2 groups across the 2 testing protocols.

RESULTS

Significant group-by-protocol interaction effects were present for both the composite equilibrium score and visual ratio. Follow-up simple main-effects analyses indicated that these measures did not differ between groups for the SOT protocol but were significantly different on the DHT-SOT.

CONCLUSIONS

The addition of dynamic head tilts to the SOT protocol resulted in subtle differences in balance function between athletes and nonathletes. Athletes demonstrated an increased ability to adapt to sensory disruptions during the DHT-SOT. Therapists should consider including active pitch and roll head tilts to the SOT when evaluating individuals with higher balance function or to detect subtle deficits in balance function.

LEVEL OF EVIDENCE

Diagnosis, level 3b.

Gaze behavior governing balance recovery in an unfamiliar and complex environment

Visuospatial information regarding obstacles and other environmental constraints on limb movement is essential for the successful planning and execution of stepping movements. Visuospatial control strategies used during gait and volitional stepping have been studied extensively; however, the visuospatial strategies that are used when stepping rapidly to recover balance in response to sudden postural perturbation are not well established. To study this, rapid forward stepping reactions were evoked by unpredictable support-surface acceleration while subjects stood amid multiple obstacles that moved intermittently and unpredictably prior to perturbation onset (PO). To prevent predictive control, subjects performed only one trial (their very first exposure to the perturbation and environment). Visual scanning of the obstacles and surroundings occurred prior to PO in all subjects; however, gaze was never redirected at the obstacles, step foot or landing site in response to the perturbation. Surprisingly, the point of gaze at time of foot-contact was consistently and substantially anterior to the step-landing site. Despite the apparent absence of 'online' visual feedback related to the foot movement, the compensatory step avoided obstacle contact in 10 of 12 young adults and 9 of 10 older subjects. The results indicate that the balance-recovery reaction was typically modulated on the basis of visuospatial environmental information that was acquired and continually updated prior to perturbation, as opposed to a strategy based on 'online' visual control. The capacity to do this was not adversely affected by aging, despite a tendency for older subjects to look downward less frequently than young adults.

Failed jump landing trials: deficits in neuromuscular control

The purpose of this investigation was to compare neuromuscular control variables during successful and failed jump landings in multiple directions (sagittal, diagonal, and lateral). All data were collected during a single leg hop stabilization maneuver, which required subjects to stand 70 cm from the center of a force plate, jump off both legs, touch a designated marker placed at a height equivalent to 50% of their maximum vertical jump, and land on a single leg for all directions. Twenty-six subjects [10 males (22+/-3.9 years of age, 70.9+/-7.6 kg, and 176.8+/-0.5 cm) and 16 females (20.6+/-0.5 years of age, 65.6+/-9.1 kg, and 166.4+/-5.9 cm)] volunteered to participate in this investigation. Muscle activation times, average preparatory, and reactive electromyographic (EMG) amplitudes were calculated for the vastus medialis, semi-membranosis, lateral gastrocnemius, and tibialis anterior. EMG data revealed that successful jump landing trials had earlier activation times and higher preparatory and reactive EMG amplitudes. There was no difference for EMG activation times or amplitudes among directions. The results indicate neuromuscular control differences between successful and failed trials because of earlier muscle onset and greater amplitude. The results also suggest that in a healthy population, the direction of the jump protocol will not affect lower extremity EMG characteristics.

A musculoskeletal model of low grade connective tissue inflammation in patients with thyroid associated ophthalmopathy (TAO): the WOMED concept of lateral tension and its general implications in disease

Background

Low level connective tissue inflammation has been proposed to play a role in thyroid associated ophthalmopathy (TAO). The aim of this study was to investigate this postulate by a musculoskeletal approach together with biochemical parameters.

Methods

13 patients with TAO and 16 controls were examined. Erythrocyte levels of Zn, Cu, Ca²⁺, Mg, and Fe were determined. The musculoskeletal evaluation included observational data on body posture with emphasis on the orbit-head region. The angular foot position in the frontal plane was quantified following gait observation. The axial orientation of the legs and feet was evaluated in an unloaded supine position. Functional propioceptive tests based on stretch stimuli were done by using foot inversion and foot rotation.

Results

Alterations in the control group included neck tilt in 3 cases, asymmetrical foot angle during gait in 2, and a reaction to foot inversion in 5 cases. TAO patients presented facial asymmetry with displaced eye fissure inclination (mean 9.1°) as well as tilted head-on-neck position (mean 5.7°). A further asymmetry feature was external rotation of the legs and feet (mean 27°). Both foot inversion as well as foot rotation induced a condition of neuromuscular deficit. This condition could be regulated by gentle acupressure either on the lateral abdomen or the lateral ankle at the acupuncture points gall bladder 26 or bladder 62, respectively. In 5 patients, foot rotation produced a phenomenon of moving toes in the contra lateral foot. In addition foot rotation was accompanied by an audible tendon snapping. Lower erythrocyte Zn levels and altered correlations between Ca²⁺, Mg, and Fe were found in TAO.

Conclusion

This whole body observational study has revealed axial deviations and body asymmetry as well as the phenomenon of moving toes in TAO. The most common finding was an arch-like displacement of the body, i.e. eccentric position, with foot inversion and head tilt to the contra lateral side and tendon snapping. We propose that eccentric muscle action over time can be the basis for a low grade inflammatory condition. The general implications of this model and its relations to Zn and Se will be discussed.