Sway-referenced Vision Research Articles

Contributing factors to postural stability in Prader-Willi syndrome

BackgroundPrader-Willi Syndrome (PWS) is a rare neurodevelopmental disorder affecting multiple functional parameters. This study examined postural stability and associated gait and neuromuscular factors in young adults with PWS. MethodsParticipants included 10 adults with PWS [7 M/3F; Body Fat % 40.61 ± 7.79]; ten normal weight (NW) adults [7 M/3F; Body Fat % 23.42 ± 7.0]; ten obese (OB) adults [7 M/3F; Body Fat % 42.40 ± 5.62]. Participants completed the Sensory Organization Test (SOT)®. Condition (C) specific and a composite equilibrium score (CES) were calculated (maximum = 100). Quadriceps strength was assessed using an isokinetic dynamometer. Three-dimensional gait analyses were completed along a 10 m walkway using a motion capture system and two force plates. A gait stability ratio (GSR) was computed from gait speed and step length (steps/m). ResultsThe PWS group had lower scores for C1, C3, C4 and CES compared to the NW (p < .039 for all) and lower scores for C4 and CES than the OB (p < .019 for both) groups, respectively. In C5 (eyes closed, sway-referenced support) and C6 (sway-referenced vision and support), 33.3% of participants with PWS fell during the first trial in both conditions (X2 [2] 7.436, p = .024) and (X2 [2] 7.436, p = .024) but no participant in the other groups fell. Those with PWS showed higher GSR than participants with NW (p = .005) and those with obesity (p = .045). ConclusionIndividuals with PWS had more difficulty maintaining standing balance when relying on information from the somatosensory (C3), visual-vestibular (C4) and vestibular systems (C5, C6). A more stable walk was related to shorter steps, slower velocity and reduced peak quadriceps torque. Participation in multisensory activities that require appropriate prioritization of sensory system(s) input for controlling balance in altered sensory environments should be routinely included. In addition, exercises targeting muscular force and power should be included as part of exercise programming in PWS.

Stroboscopic Vision as a Dynamic Sensory Reweighting Alternative to the Sensory Organization Test.

The sensory organization test (SOT) is a standard for quantifying sensory dependence via sway-referenced conditions (sway-referenced support and sway-referenced vision [SRV]). However, the SOT is limited to expensive equipment. Thus, a practical version of the SOT is more commonly employed-the clinical test for sensory integration in balance; however, it fails to induce postural instability to the level of SRV. Determine if Stroboscopic vision (SV), characterized by intermittent visual blocking, may provide an alternative to the SRV for assessing postural stability. Descriptive laboratory study. Research laboratory. Eighteen participants (9 males, 9 females; age = 22.1 [2.1]y, height = 169.8 [8.5]cm, weight = 66.5 [10.6]kg). Participants completed the SOT conditions, and then repeated SOT conditions 2 and 5 with SV created by specialized eyewear. A repeated-measures analysis of variance was completed on the time-to-boundary metrics of center-of-pressure excursion in the anteroposterior and mediolateral directions in order to determine the difference between the full-vision, SV, and SRV conditions. Postural stability with either SRV or SV was significantly worse than with full vision (P < .05), with no significant difference between SV and SRV (P > .05). Limits of agreement analysis revealed similar effects of SV and SRV except for unstable surface mediolateral time-to-boundary. In general, SV was found to induce a degree of postural instability similar to that induced by SRV, indicating that SV could be a portable and relatively inexpensive alternative for the assessment of sensory dependence and reweighting.

Balance in Virtual Reality: Effect of Age and Bilateral Vestibular Loss.

Quantitative balance measurement is used in clinical practice to prevent falls. The conditions of the test were limited to eyes open, eyes closed, and sway-referenced vision. We developed a new visual perturbation to challenge balance using virtual reality (VR), measuring postural stability by a Wii Balance Board (WBB). In this study, we recorded balance performance of 116 healthy subjects and of 10 bilateral vestibular loss patients using VR to assess the effect of age and the effect of total loss of vestibular function. We used several conditions: eyes open (normal visual inputs), eyes closed (no visual inputs), stable visual world (vision referenced), and perturbed visual world (visual perturbation) at different amplitudes of perturbation. Balance under these visual conditions was assessed on the WBB (stable support surface) and on the WBB plus foam rubber (unstable support surface). In healthy subjects, we found that the percentage of falls increased with age and with the amplitude of perturbation for both conditions: WBB or WBB + foam. Moreover, we can define a threshold for falls in each age group as the amplitude of perturbation which induced falls. For bilateral vestibular loss patients, on the WBB + foam, all of them failed with eyes closed and with perturbed visual world even at the minimal amplitude of perturbation. Finally, we observed that stable visual world induced fewer falls than eyes closed whatever the subject's group (healthy or bilateral vestibular loss) and whatever the age decade. VR allowed us to develop a useful new tool with a wide range of visual perturbations. Rather than only two levels of visual condition (eyes open and eyes closed), the VR stimulus can be continuously adjusted to produce a visual perturbation powerful enough to induce falls even in young healthy subjects and which has allowed us to determine a threshold for falls.

Impact of alternative footwear on human balance

Alternative footwear are those that are most commonly used for casual or recreational purposes, over the course of the day. The purpose of this study was to examine the effects of three forms of alternative footwear (thong style flip-flops, clog style Crocs®, and Vibram Five-Fingers®) on balance with a low-intensity workload. Eighteen healthy male adults (age: 22.9 ± 2.88 years; height: 179 ± 6.0 cm; mass: 81.3 ± 8.8 kg) participated in this study. Balance performance along with electromyographic (EMG) measures was assessed with sensory organization test (SOT) and motor control test on the Neurocom Equitest, while donning alternative footwear, prior to and after a one-mile walk at a self-selected pace. Sway velocities and root-mean-square sway, SOT equilibrium scores, postural response latencies, and EMG measures from lower leg muscles were analysed using a 3 × 2 (footwear × time) repeated-measures ANOVA. Results from balance variables revealed a significant main effect difference for footwear in the eyes closed and eyes open sway-referenced vision conditions and a significant main effect difference for time in the eyes open, eyes open sway-referenced vision, and eyes open sway-referenced platform conditions. Pairwise comparisons revealed MIN demonstrating significantly greater balance performance in the pretest condition and the post-test demonstrating significantly lower balance performance. Greater balance performance from MIN could be attributed to the barefoot design suggesting an increase in somatosensory feedback from the plantar surface, particularly during absent or conflicting visual feedback. The lower balance performance seen in post-test could be attributed to the one-mile walk, suggesting that even a transient physiological workload could be sufficient to cause balance decrements in alternative footwear.

Effect of tetrabenazine on computerized dynamic posturography in Huntington disease patients

BackgroundImpairment in computerized dynamic posturography scores has been documented in Huntington disease patients. Tetrabenazine is approved to treat chorea in Huntington disease, but its effect on posturography scores, and balance in general, is unknown. Materials and methodsWe designed a study to test computerized dynamic posturography performance while taking tetrabenazine and after stopping tetrabenazine for at least three days. Results10 Huntington disease patients were studied both ON and OFF tetrabenazine. The composite score was statistically different between ON and OFF conditions and both conditions were significantly worse than reference scores. There was no significant difference between ON and OFF trials in the number of falls. A significant improvement on Sensory Orientation Test conditions 3 (sway-referenced vision) and 5 (sway-referenced motion of the support surface and eyes closed) was seen while ON tetrabenazine. Strategy scores 1–3 were also significantly different while ON tetrabenazine. ConclusionThese findings suggest that tetrabenazine aided patients in gating out of abnormal visual cues when other sensory modalities were available, as well as in gating out abnormal kinesthetic cues when visual cues were not available. It could not help with gating out of simultaneous abnormal visual and somatosensory cues. Thus, tetrabenazine can improve postural stability when one sensory modality is irrelevant, but this effect is not sustained when multiple abnormal sensory modalities are present. This is the first study supporting the use of any medicine to treat balance problems in Huntington disease.

Immediate Effects of Ischemic Compression on Neck Function in Patients With Cervicogenic Cephalic Syndrome

ObjectiveCervicogenic cephalic syndrome (CCS), a group of diseases, consists of cervicogenic headache and dizziness. These symptoms may cause loss of physical function compared with other headache and dizziness disorders. The purpose of this case-control study was to assess the clinical effects of ischemic compression (IC) in patients with CCS. MethodsTwenty-seven subjects with chronic neck pain (persisting for >3 months) and 26 healthy volunteers were examined. Subjects with organic lesion of the ear, nose, throat, eye, or central nervous system were excluded. The CCS group received IC over the maximal tender points of the origin of the posterior nuchal muscle. Sensory organization test (SOT) scores, cervical range of motion (ROM), and isometric strength of neck were measured before IC and after IC. ResultsThe ROM of the cervical spine increased in all directions after IC (P < .0083) in the CCS group, and isometric strength in the CCS group rose in all directions after IC (P = .000). There was a significant difference in ankle strategy score under the sway-referenced vision and fixed support condition (P = .003) between the control group and CCS before IC. The ankle strategy score of the CCS group improved substantially after IC under eyes closed and sway-referenced support conditions (P = .003). The visual and vestibular ratios in the CCS group also increased after IC (P = .006 and P = .002, respectively). ConclusionsThe findings of this study showed that ROM of the cervical spine and isometric strength increased in all directions, and the SOT scores showed increased postural stability under conditions with swayed reference support after IC in the CCS group. The ratios for vestibular and visual function also increased after IC in the CCS group.

Effects of swimming on eye hand coordination and balance in the elderly.

To evaluate the effects of swimming on upper extremity motor control, and balance in elderly population. Cross-sectional study. The biomechanical laboratory in a tertiary hospital. The swimming group consisted of 20 swimmers (n_20, 65.4 ± 5.5 years) who received regular swimming exercise for more than 2 years. The control group consisted of 34 healthy active subjects (n_34, 67.4 ± 5.7 years) who have regular exercises other than swimming. The eye hand coordination was evaluated by calculating the mean reaction time required in accurately pointing onto the center of the target sensors that come in three different sizes (1 cm, 1.5 cm, and 2 cm in diameter). The SMART Balance Master device was used to measure posture balance. The maximal stability, center of pressure (COP) velocity, and percentage ankle strategy were obtained under six different balance conditions. In the testing of upper extremity motor control, the swimming group had significant shorter mean reaction time as compared with the control group in all three target sensor sizes (p < 0.05). In balance testing, the swimming group had significant greater percentage of ankle strategy during eyes closed and fixed support (EC), and sway-referenced vision and support (SVSS) conditions as compared with the control group (p < 0.05). Regular swimming exercise may result in improved eye hand coordination as faster and more accurate repetitive movements. Swimming may also result in improved balance function under few complicated balance conditions.

Improvement Of Balance And Neck Fitness After Prolotherapy: Alternative Treatment Of Cervico-cephalic Syndrome

Prolotherapy becomes a promising alternative therapy for cervico-cephalic syndrome. Recent studies showed the neck plays a important role in balance performance. In this study, we tested the balance performance and neck fitness of the patients with cervico-cephalic syndrone before and after prolotherapy. Objective: To evaluate fitness and balance performance outcomes of the patients undergoing dextrose prolotherapy for cervico-cephalic syndrome METHODS: twenty-six male (Age: 37.8±14.0, Body height: 172.1±8.0 cm) and tewnty-one female (Age: 39.6±12.1, Body height: 157.9±7.1 cm) patients, who suffered from cervico-cephalic syndrome, received prolotherapy. The injections were gived on the entheses along bilateral superior, inferior nuchal line and mastoid process. Their balance performance and neck fitness were measured before and after prolotherapy. Balance performance was measured by Smart Balance Master (Neurocom International Inc., USA), including Sensory Organization Test (SOT). The SOT evaluated 6 consitions including (1) eyes open and fixed support (EO); (2) eyes closed and fixed support (EC); (3) sway-referenced vision and fixed support (SV); (4) eyes open and sway-referenced support (SS); (5) eyes closed and sway-referenced support (ECSS); (6) sway-referenced vision and support (SVSS). Cervical range of motion (ROM) and isometric strength were measured by microFET3 (HOGGAN Health Industries, USA). RESULTS: Equilibrium score showed significant difference in EC (92.2±3.2 vs. 92.8±2.6) and SS (83.8±10.7 vs. 86.8±9.0). Somatosensory ratio (0.967±0.02 vs. 0.975±0.01) and visual ratio (0.879±0.11 vs.0.911±0.08) increased significantly. Cervical ROM was found significantly improved in lateral flextion to right (33.1±8.7 vs. 34.8±7.4) and left (33.1±7.8 vs. 35.7±9.0). Cervical isometric strength was statistically different in lateral flextion to left and rotation to left. CONCLUSION: In this prospective study, the patients with cervico-cephalic syndrome demonstrated objective improvements in their flexibility and isometric strength of the neck, and balance performance after dextrose prolotherapy.

Impairment of Stance Control in Children With Sensory Modulation Disorder

To compare stance control between children with sensory modulation disorder (SMD) and typically developing children in various visual and somatosensory conditions. Thirty-one children participated in this study, including 17 children with SMD and 14 matched typically developing children. The Sensory Profile was used to screen for sensory modulation problems, which were further confirmed by measures of electrodermal response and the Evaluation of Sensory Processing. Stance parameters for an assessment of postural stability were obtained with a dual-axis accelerometer on the lumbar area. The children with SMD presented atypical sensory responses in terms of both electrophysiological and behavioral measures. The results for stance showed a greater body sway in the SMD group than in the control group (p < .05). However, the group difference was not always significant under the conditions of reliable somatosensory input and sway-referenced vision. Our findings first confirmed impaired stance control in children with SMD.

Differential Anti-aging Effects of Tai Chi Chuan on Aging Process of Balance

PURPOSE: To differentiate the anti-aging effect of Tai Chi Chuan (TCC) on the aging process of balance. METHODS: A 2×2 between age and TCC factorial design were studied at a biomechanical laboratory of a medical center. Twenty six old TCC practitioners (8 men and 18 women aged 52 to 76 years), 14 healthy and active old non-practitioners (4 men and 10 women aged 65 to 76 years), 12 young TCC practitioners (4 men and 9 women aged 18 to 26 years), and 19 young non-TCC practitioners (7 men and 12 women aged 19 to 33 years) were recruited for this study. A computerized posturography, the Smart Balance Master (Neuro Com Inc., Clackmas, Oregon, USA) was employed to measure postural stability under the defined conditions. RESULTS: About the TCC effects, significant differences (p<.0083) were found in eyes open and sway-referenced support (SS), eyes closed and sway-referenced support (ECSS), and sway-referenced vision and support (SVSS) conditions. Strategy analysis revealed the TCC group use more ankle strategy (p<.0083) only in SVSS condition than non-TCC group. Visual and vestibular ratios of TCC group were significantly better (p<.0125) than the non-TCC group. About the age effect, the younger subjects had significantly higher (p<.0083) equilibrium score than old subjects in all conditions. Significant differences (p<.0083) were found in ankle strategy usage of SS, ECSS, and SVSS conditions. The significant interaction effects of the age and the TCC were observed in the equilibrium score of the SVSS condition. There were also significant interaction effects on use ankle strategy usage of ECSS and SVSS conditions. CONCLUSION: TCC has delay effect, rather than rejuvenation or maintenance effect, on the aging process of balance, especially in the conditions of more challenge or the condition deprive of certain sensory information.

Quantitative Assessment Of The Effect Of Ischemic Compression On Patients With Cervicogenic Headache.

Cervicogenic headache has the greatest potential of losing physical function when compared with the other groups of headache disorders. Dizziness and/or unsteadiness are also common symptoms of chronic whiplash-associated disorders. The diagnosis of cervicogenic dizziness is characterized by dizziness and dysequilibrium that is associated with neck pain in patients with cervical pathology. In addition to headache, dizziness and/or dysequilibrium, cervical lesions may also result in ophthalmic, olfactory and/or throat complaints. Collectively, we introduce the term "cervicogenic cephalic syndrome" (CCS). We also conduct a quantitative assessment to evaluate the treatment effect of ischemic compression on patients with CCS. PURPOSE: To access the effect of ischemic compression on the neck function of patients with CCS. METHODS: Twenty-three subjects, 10 males and 13 females, with chronic neck pain were recruited. An electronic instrument of combined goniometer and muscle test will be used to measure flexibility and isometric strength of neck. The sensory organization test (SOT) will conducted to assess the balance control of subjects. During the SOT, subjects will be exposed to 6 combinations of visual and support surface conditions as follows: (1) eyes open and fixed support (EO), (2) eyes closed and fixed support (EC), (3) sway-referenced vision and fixed support (SV), (4) eyes open and sway-referenced support (SS), (5) eyes closed and sway-referenced support (ECSS), and (6) sway-referenced vision and support (SVSS). RESULTS: The average age were 40.6 ± 17.6, and 44.4 ± 11.0 years old, in male and female respectively. The average duration of symptoms in male patients are 11.1±12.0 and female patients 7.0 ± 3.7 years. The ROM of cervical spine are increased in all direction after treatment (P < 0.05). The isometric strength increased in left lateral flexion and rotation after treatment (P <0.05). After treatment, the subjects showed increased postural stability in the SS, ECSS, and SVSS conditions of SOT. The visual and vestibular ratios are also increased after treatment. The ankle strategy improved in the SV, SS, ECSS, and SVSS conditions of SOT. CONCLUSION: ischemic compression is effective in treating patients with CCS. SOT could be a quantitative assessment tool of neck function.

Differential Anti-aging Effects Of Tai Chi Chuan On Aging Process Of Balance

Tai-Chi Chuan (TCC) is a traditional Chinese martial art. Debates had been made about the anti-aging effects of TCC in many researches. However, no previous research studies about the interaction effect of age and TCC in aging process of balance. We conduct a two-factor designed study to evaluate the antiaging effect of TCC on balance. PURPOSE: To determine anti-aging effects and the interaction effects of aging and TCC on balance. METHODS: Four groups (old TCC group, n=26, age=68.3± 6.2, duration of practice= 13.3± 9.6; young TCC group, n=13, age=21.8±2.5, duration of practice= 3.0± 1.7; old control group, n=14, age=69.1± 3.1; young control group, n=19, age=24.8± 3.8) of subjects were tested with The Smart Balance Master (Neuro Com Inc., Clackmas, Oregon, USA) to acquire postural stability measurement. The sensory organization test (SOT) will conducted to assess the balance control of subjects. During the SOT, subjects will be exposed to 6 combinations of visual and support surface conditions as follows: (1) eyes open and fixed support (EO), (2) eyes closed and fixed support (EC), (3) sway-referenced vision and fixed support (SV), (4) eyes open and sway-referenced support (SS), (5) eyes closed and sway-referenced support (ECSS), and (6) sway-referenced vision and support (SVSS). RESULT: TCC effects are significant in all the counter-active conditions (SV,SS, ECSS, SVSS). Age effects are significant in all conditions. Interaction effects are significant in ECSS and SVSS. Main effects of TCC and age are both significant in visual, vestibular and preferential ratios. Interaction effects are not significant in all ratios. CONCLUSION: TCC can improve postural stability and prevent balance deterioration during aging process.

Balance Performance In Middle-aged Subjects With Cervical Spondylosis

Cervical spondylosis is a common progressive disorder in aging cervical spine. Sensory systems are important for balance maintenance. Poor postural control in older people is associated with increased risk of falling. PURPOSE: This study was to evaluate the impact of cervical spondylosis in the middle-aged group, compared with the young control group, on balance performance, neck range of motion (ROM) and isometric muscle strength. METHODS: Fifteen middle-aged subjects (age: 52±7years) with cervical spondylosis, diagnosed by cervical spine radiographs, and fifteen young subjects (age: 22±2years) underwent sensory organization test (SOT) using SMART Balance Master System. SOT evaluates postural control under 6 conditions including (1) eyes open and fixed support (EO); (2) eyes closed and fixed support (EC); (3) sway-referenced vision and fixed support (SV); (4) eyes open and sway-referenced support (SS); (5) eyes closed and sway-referenced support (ECSS); and (6) sway-referenced vision and support (SVSS). Microfet3 was used to assess neck ROM and isometric strength. Comparisons between groups were made using independent t-test. RESULTS: Equilibrium scores showed significant differences between groups in EO (94.4±1.7 vs. 95.9±1.0), SS (80.1±15.5 vs. 91.2±2.6), ECSS (57.0±16.4 vs. 70.6±4.9) and SVSS (59.7±15.1 vs. 78.7±6.3). Vis (0.8±0.2 vs. 1.0±0.02) and Vest (0.6±0.2 vs. 0.7±0.1) ratios had significant differences between groups. Neck ROM was significantly larger and isometric rotational muscle strength was also significantly stronger in the young group than the middle-aged group. CONCLUSION: Cervical spondylosis was diagnosed in the milled-aged group and might contribute to the change of neck ROM and isometric strength. ROM and strength were both deteriorated in the middle-aged group compared to the young group. Sensory ratios indicate the ability to use the visual or vestibular system and reflect in a sense the neck function. Poor balance performance in the middle-aged group may be in part attributed to poor neck function, reflected in the lower sensory ratios.

Assessment of fibula osteoseptocutaneous flap donor‐site morbidity using balance and gait test

To assess the functional deficits in gait and balance after fibular osteoseptocutaneous flap harvest, a case-control study in a hospital-based biomechanical laboratory was conducted. Eleven patients receiving fibula osteoseptocutaneous flaps were enrolled as study group and 10 age-matched and healthy subjects as a control group. The average postoperative period at the time of evaluation was 27.4 months (range: 10 to 68 months) and the average age at the time of evaluation was 52.1 years (range: 38 to 76 years). The balance test by Smart Balance Master and gait analysis were used for objective assessment of the donor leg function postoperatively. No statistical differences were observed in the kinetic and kinematic variables of gait analysis except double support time in both the groups. There were also no significant differences in simple static balance test (eyes open, eyes closed, swaying vision, eyes open with swaying surface, and sway-referenced vision and support). Significant differences were observed in more difficult task (eye closed with swaying support) and in the use of ankle strategy for maintaining maximum balance. In the dynamic balance test only specificity of the forward left direction determined significant difference in reaction time of movement control of gravity. The results of ankle strategy usage and dynamic balance indicated deficits of ankle muscle torque. Necessary postoperative physical training is required for ankle muscle torque and vestibular sense.

Sensorimotor specificities in balance control of expert fencers and pistol shooters

Motor skills during sport activity are influenced by practice-related constraints and leads to the development of appropriate postural sensorimotor strategies. Fencing is highly requiring visual monitoring and high-speed motor skills while retaining efficient balance control. Conversely, pistol shooting is a static activity requiring a high control of body sway. This study aimed to evaluate balance control and the related neurosensory organisation through reproducible postural tasks with and without sensory conflict. Twelve expert fencers, 10 expert shooters and 10 sedentary controls have performed a static posturographic test and a sensory organisation test (in 6 different sensory situations based upon sway-referenced vision and support surface, C1 to C6). Shooters yielded a better balance control during C1 (eyes open) and C2 (eyes closed) than fencers and controls. Fencers showed a better balance control in C5 (eyes closed with sway-referenced support surface) than shooters and controls. While this study confirms the beneficial effects of physical activities on balance control, a differential effect on balance characteristics due to the acquired specific motor skills was also noted. In addition to high proprioceptive sensitivity in sportsmen, dynamic constraints in fencing force fencers to permanently select the most relevant information to manage better sensory conflicting situations.

Effects of an Anterior Ankle–Foot Orthosis on Postural Stability in Stroke Patients with Hemiplegia

To evaluate the effects of an anterior leaflet ankle-foot orthosis (AFO) on postural stability in stroke patients with hemiplegia. Twenty-one stroke patients with hemiplegia resulting from new-onset stroke and ten normal subjects were included in this study. The SMART balance master system was used to assess the postural stability by measuring the ankle strategy, maximal stability, and velocity of center-of-gravity (COG) movement under the following six conditions: (1) eyes open and fixed support (EOFS), (2) eyes closed and fixed support (ECFS), (3) sway-referenced vision and fixed support (SVFS), (4) eyes open and sway-referenced support (EOSS), (5) eyes closed and sway-referenced support (ECSS), and (6) sway-referenced vision and support (SVSS). Each patient was tested with and without an anterior AFO as compared with normal subjects. When wearing an anterior AFO, patients used ankle strategy more than hip strategy to maintain postural stability in all the six sensory conditions (P < 0.05). An anterior AFO also provided stroke patients with better maximal stability under relatively challenging conditions such as SVFS, EOSS, and ECSS (P < 0.05), but the effect was not apparent in the conditions without external perturbation (EOFS and ECFS) and the most difficult condition (SVSS). The velocity of COG movement was lowered when wearing an anterior AFO in stroke patients, and significant differences existed in the EOFS, ECFS, ECSS, and SVSS conditions (P < 0.05). In the early stage of recovery, the use of an anterior AFO may assist stroke patients with hemiplegia to improve their postural stability.

The Effect of Maximal Exercise on Static and Dynamic Balance in Athletes and Non-Athletes

Abstract Zemkova E, Viitasalo J, Hannola H, Blomqvist M, Konttinen N, Mononen K. The effect of maximal exercise on static and dynamic balance in athletes and non-athletes. Med Sport 2007, 11(3): 70-77. Introduction : Though the effect of different forms of exercise on static balance has been studied, there are only scarce reports concerning its influence on dynamic balance. Aim of the study : The study deals with postural sway response to maximal exercise. Methods : A group of 30 athletes and 10 non-athletes underwent in random order in different days balance tests prior to and after maximal exercise bout on the cycle ergometer. Pre-exercise protocol comprised of standard SOT and HS SOT conditions based on the EquiTest dynamic posturography system. In the SOT, during the first three conditions with eyes open, eyes closed, and sway-referenced vision the support surface was fixed and during the same next three conditions the support surface was sway-referenced. In the HS SOT, support surface was either fixed or sway-referenced while subject´s eyes were closed and their head was moving in roll and pitch planes. After exercise only selected conditions were repeated, two static with subjects eyes open and closed and two dynamic with their eyes closed and sway-referenced vision.

Modeling postural instability with Galvanic vestibular stimulation

In this study the effect of a pseudorandom binaural bipolar Galvanic stimulus generated by a sum of nonharmonically related sine waves on postural control was functionally assessed using computerized dynamic posturography (CDP), and the results compared to vestibulopathic patient populations and astronauts exposed to microgravity. The standardized CDP test battery comprised six sensory organization tests (SOTs) that combined three visual conditions (eyes open, eyes closed, and sway-referenced vision) with two proprioceptive conditions (fixed and sway-referenced support surfaces). Subjects (12) performed 18 randomized trials (three trials of each of the six SOTs) as a baseline, repeated the 18 trials with Galvanic vestibular stimulation (GVS), and then performed a post-GVS baseline. A 10 min rest period was inserted between each test battery. Anterioposterior postural sway increased significantly and was in the abnormal range (fifth percentile) during GVS for SOTs where visual input was compromised (sway-referenced surround) or absent. Postural stability returned to baseline when GVS was removed. An analysis of sensory input scores (somatosensory, visual, and vestibular) demonstrated the specificity of GVS in distorting vestibular input to postural control. The SOT scores observed in astronauts on landing day did not differ significantly to that generated by GVS in our normal subjects. GVS also induced a similar pattern of instability on CDP as profound bilateral vestibular loss, although not as severe. The results suggest that unpredictably varying GVS quantitatively and qualitatively models postural instability of vestibular origin.

Frequency spectral characteristics of standing balance in children and young adults

Past research has shown that spectral frequency characteristics of a balance control system may be useful for early detection of minor changes in the system. Since there is a lack of information regarding the frequency spectrum of children’s balance control system, this study was undertaken to investigate and compare the spectral frequency characteristics of standing balance control between children and young adults under altered sensory environments. Seventeen children (9 females, 8 males, mean age 7.8±0.9 years) and the same number of female and male young adults (mean age 21.1±1.3 years) were tested for standing balance under six sensory conditions. These conditions were created by crossing the three levels of the visual factor (open eye, closed eye, sway-referenced vision) with the two levels of the somatosensory factor (fixed foot support, compliant foot support). The median spectral frequencies of the shear forces in the anterior–posterior (A/P) and the medial–lateral (M/L) directions were used as dependent variables. The results showed that children had higher median spectral frequency of the A/P shear force than young adults and this difference was not affected by the somatosensory factor. The median spectral frequency in the M/L direction was not different between the groups. The higher rate of body mass vibration of children in the A/P direction implies that children may not have fully developed the ankle strategy for maintaining standing balance, but nonetheless have developed the same efficiency of using vision for their reference of standing balance.

Vestibular plasticity following orbital spaceflight: recovery from postflight postural instability.

Results of previous studies suggested that the vestibular mediated postural instability observed in astronauts upon return to earth from orbital spaceflight may be exacerbated by an increased weighting of visual inputs for spatial orientation and control of movement. This study was performed to better understand the roles of visual and somatosensory contributions to recovery of normal sensori-motor postural control in returning astronauts. Preflight and postflight, 23 astronaut volunteers were presented randomly with three trials of six sensory organization test (SOT) conditions in the EquiTest system test battery. Sagittal plane center-of-gravity (COG) excursions computed from ground reaction forces were significantly higher on landing day than preflight for those test conditions presenting sway-referenced visual and/or somatosensory orientation cues. The ratio of summed peak-to-peak COG sway amplitudes on the two sway-referenced vision tests (SOTs 3 + 6) compared to the two eyes closed tests (SOTs 2 + 5) was increased on landing day, indicating an increased reliance on visual orientation cues for postural control. The ratio of peak-to-peak COG excursions on sway-referenced surfaces (SOTs 4, 5 & 6) to an earth fixed support surfaces (SOTs 1, 2 & 3) increased even more after landing suggesting primary reliance on somatosensory orientation cues for recovery of postflight postural stability. Readaptation to sway-referenced support surfaces took longer than readaptation to sway-referenced vision. The increased reliance on visual and somatosensory inputs disappeared in all astronauts 4-8 days following return to earth.