Demonstration of the Effect of Centre of Mass Height on Postural Sway Using Accelerometry for Balance Analysis

The effect of center of mass (COM) height on stand-still postural sway analysis was studied. For this purpose, a measurement apparatus was set up that included an accelerometry unit attached to a rod: three plumb lines, positioned at 50 cm, 75 cm, and 100 cm to the end of the rod, each supported a plumb bob. Using a vice mechanism, the rod was inclined from vertical (0 degree inclination) in steps of 5 degrees to 90 degrees. For each inclination, the corresponding inclination angle was manually measured by a protractor, and the positions of the three plumb bobs on the ground surface were also manually measured using a tape measure. Algebraic operations were used to calculate the inclination angle and the associated displacements of the plumb bobs on the ground surface from the accelerometry data. For each inclination angle, the manual and accelerometry calculated ground displacement produced by each plumb bulb were close. It was demonstrated that the height of COM, where the measurement was taken, affected the projected displacement on the ground surface. A higher height produced a greater displacement. This effect has an implication in postural sway analysis where the accelerometry readings may need comparison amongst subjects with different COM heights. To overcome this, a method that normalized the accelerometry readings by considering the COM height was proposed, and the associated results were presented

The magnitude of the effect of calf muscles fatigue on postural control during bipedal quiet standing with vision depends on the eye-visual target distance

The purpose of the present experiment was to investigate whether, with vision, the magnitude of the effect of calf muscles fatigue on postural control during bipedal quiet standing depends on the eye-visual target distance. Twelve young university students were asked to stand upright as immobile as possible in three visual conditions (No vision, Vision 1m and Vision 4m) executed in two conditions of No fatigue and Fatigue of the calf muscles. Centre of foot pressure displacements were recorded using a force platform. Similar increased variances of the centre of foot pressure displacements were observed in the fatigue relative to the No fatigue condition for both the No vision and Vision 4m conditions. Interestingly, in the vision 1m condition, fatigue yielded: (1) a similar increased variance of the centre of foot pressure displacements to those observed in the No vision and Vision 4m conditions along the medio-lateral axis and (2) a weaker destabilising effect relative to the No vision and Vision 4m conditions along the antero-posterior axis. These results evidence that the ability to use visual information for postural control during bipedal quiet standing following calf muscles fatigue is dependent on the eye-visual target distance. More largely, in the context of the multisensory control of balance, the present findings suggest that the efficiency of the sensory reweighting of visual sensory cues as the neuro-muscular constraints acting on the subject change is critically linked with the quality of the information the visual system obtains

Perception of Lower Extremity Loads in Stroke Survivors

Objective: This study aimed to improve our understanding of static and dynamic lower extremity sensory perception and the impact of sensory impairments on the control of walking in stroke survivors. Methods: Using a custom, real-time unloading system, we tested load perception at heel strike, mid stance and push off in 10 stroke survivors and compared their performance to 10 age-matched and 5 young adult control subjects. Dynamic load perception was based on a judgment of which leg was bearing more load, which was altered on a step by step basis. We also examined lower extremity static load perception, coordination, proprioception, balance, and gait symmetry. Results: The stroke survivors performed significantly worse than the control subjects in dynamic load perception, coordination, proprioception, balance and gait symmetry. Gait symmetry correlated with static and dynamic load perception measures but not with age, proprioception, coordination, and balance. Conclusions: Sensory deficits related to load detection in the impaired limb could result in an increased uncertainty of limb load and a gait strategy in which stroke survivors minimize loading of the impaired limb. Significance: This new method of measuring lower extremity dynamic load perception provides a framework for understanding gait-related sensory impairments in stroke survivors

Effect of coordination training on proprioception of the functionally unstable ankle

Abstract: Exercises to improve joint proprioception and coordination of the functionally unstable ankle are advocated throughout the literature, yet there is little evidence that these exercises have any effect on proprioception and balance. The purpose of this study was to determine the effects of a 6-week coordination and balance training program on proprioception of subjects with functional ankle instability. Forty-five subjects (age = 22.53 ± 3.95 years, height = 172.04 ± 10.0 cm, weight = 71.72 ± 15.7 kg) were randomly placed into a control (Group 1), sham (Group 2), or experimental (Group 3) group. The experimental group trained 3 days per week, 10 minutes each day, performing various balance and proprioception exercises. Postural sway and active and passive joint position sense were assessed. Analysis of variance for postural sway modified equilibrium score for anterior and posterior sway, as well as medial and lateral sway revealed significant four-way interactions. Tukey post hoc analyses revealed that Group 3 performed significantly better (p < .05) than Group 1 and Group 2 on the posttests. There were no significant differences for joint position sense or postural sway index. Results suggest that balance and coordination training can improve some measures of postural sway. It is still unclear if joint position sense can be improved in the functionally unstable ankle

Sensory and methodological aspects in biomechanical research of postural control and clinical fields of application

The human senses constitute a highly complex system based on various sensory organs, afferent pathways, and central processing locations, which allow us to interact with the environment, but also with ourselves. A further domain is important to achieve this interaction: the motor system, which allows linguistic communication and locomotion, for example. It becomes evident that sensory receptors work as a source of information to initiate, optimize, or cease motor activity. One generic term for such sensory sources is the somatosensory system, which is mainly based on receptors located in muscles, tendons, and the skin (cutaneous sensitivity). In this regard, it has been shown that cutaneous sensitivity contributes to human balance regulation. However, there are still debates concerning the exact role of plantar (foot sole) receptor inputs in particular, and how their isolated contribution to, e.g., balance regulation may be assessed accordingly. To investigate the interaction between plantar cutaneous sensitivity and human balance capabilities, several aspects need to be considered which are still controversial and inconclusive in the scientific community. For example, when assessing cutaneous vibration sensitivity, it is well-known that increasing vertical forces of the contactor toward the skin usually result in improved sensitivity. However, it has not been profoundly investigated whether assessing plantar vibratory sensitivity differs when comparing a standing or sitting posture, which obviously involves different contactor forces. In addition, many studies implementing cutaneous sensitivity show certain limitations with respect to adequate data analyses. A similar aspect also applies when assessing balance performance: devices allowing an investigation of dynamic balance performance (induced by unexpected platform perturbations while standing, for example) have only been partially investigated with regard to their biomechanical quality criteria, such as reliability. With these considerations in mind, the present doctoral thesis is based on five published studies. Study 1 investigates if plantar sensitivity is influenced by different body positions when collecting data. Study 2 asks how to appropriatly analze plantar sensitivity data. Study 3 examines the reliability of dynamic balance responses using the so-called Posturomed device, and Study 4 identifies the isolated role of plantar inputs on balance responses, when an acute sensory manipulation is induced that exclusively affects plantar aspects. Ultimately, clinical fields of application (based on the previous four studies) are highlighted in Study 5. The main findings of the first four studies can be summarized as follows. First, higher contact forces when standing compared to sitting did not influence plantar sensitivity. This is an important finding, as plantar sensitivity tests (often performed during sitting) may, hence, be brought into context with balance tests usually performed during standing. Second, plantar sensitivity data are shown to exhibit heteroscedasticity, meaning that the measurement error increases as the values increase. In Study 2, we provided an easy-to-follow example for how to account for heteroscedasticity by logarithmizing the raw data, and how to control whether this approach was successful in eliminating heteroscedasticity. Third, dynamic balance responses assessed via the Posturomed device exhibit an overall good reliability. Occasional significant differences were shown to be clinically non-relevant, identified by root mean square error calculations. Fourth, a permanent plantar sensory manipulation (hypothermia) was successfully achieved and maintained throughout data collection. Study 4 showed that the reduced plantar sensory input due to the hypothermic manipulation was compensated during more unchallenging balance conditions (standing still). There was no full compensation during more challenging balance conditions (unexpected platform perturbations during standing), however, with the body reacting with cautious motor behavior. This became evident by decreased outcome measures following hypothermic plantar sensory manipulation. These four studies shed further light onto investigations combining sensory and motor tests, especially with regard to physiological and methodological aspects that should be considered when analyzing and interpreting associated data. Finally, this doctoral thesis also provides an example of identifying clinical fields of application concerning sensory-focused research. In Study 5, we highlight the role of sensory research in the (early) diagnosis of diseases associated with cognitive decline. For this purpose, various instruments such as sensory tests or coordinative motor tests are implemented. Preliminary results suggest that not only classical cognitive parameters and questionnaires should be used to identify and better understand cognitive decline.Die menschlichen Sinne stellen ein sehr komplexes System dar, welches auf verschiedenen sensorischen Organen, afferenten Leitungsbahnen und zentralen Verarbeitungsstellen basiert und es uns ermöglicht, mit der Umwelt, aber auch mit uns selbst, zu interagieren. Dahingehend ist eine weitere wichtige Domäne wichtig, um diese Interaktion zu bewerkstelligen: das motorische System, welches etwa eine sprachliche Kommunikation oder auch die Fortbewegung ermöglicht. Es wird somit offensichtlich, dass sensorische Rezeptoren eine Informationsquelle darstellen, um motorische Aktivität zu initiieren, zu optimieren oder zu beenden. Ein grundlegender Terminus für solch sensorische Quellen ist das somatosensorische System, welches überwiegend auf Rezeptoren in Muskulatur, Sehnen und der Haut (kutane Sensibilität) beruht. Diesbezüglich wurde bereits aufgezeigt, dass die kutane Sensibilität einen Beitrag bei der menschlichen Gleichgewichtsregulation leistet. Allerdings existieren dabei nachwievor Diskussionen in Bezug auf die genaue Bedeutung plantarer (die Fußsohle betreffend) Rezeptor-Inputs und inwieweit deren isolierte Bedeutung bei der Gleichgewichtsregulation entsprechend ermittelt werden kann. Um die Interaktion zwischen der kutanen Sensorik der Fußsohle und der menschlichen Gleichgewichtsfähigkeit zu erforschen, sollten verschiedene Aspekte berücksichtigt werden, welche nachwievor kontrovers und nicht eindeutig in der Wissenschaft diskutiert werden. Bei Erhebungen der kutanen Vibrationssensibilität, als Beispiel, ist bereits bekannt, dass erhöhte Vertikalkräfte, mit denen der Vibrationsstößel gegen die Haut appliziert ist, generell zu einer verbesserten Sensibilität/Sensorik führen. Allerdings wurde noch nicht klar erforscht, ob sich die plantare Vibrationssensibilität zwischen einer stehenden und sitzenden Haltung der Probanden/innen unterscheidet, wobei hier natürlich unterschiedliche Vertikalkräfte der Stößel wahrscheinlich sind. Darüber hinaus zeigen viele Studien, welche die Hautsensibilität untersuchen, gewisse Limitierungen in Bezug auf eine adäquate Datenanalyse. Ein sehr ähnlicher Aspekt trifft auch auf die Evaluierung der Gleichgewichtsfähigkeit zu: Messgeräte, welche dabei eine Erfassung der dynamischen Gleichgewichtsfähigkeit zulassen (z.B. eingeleitet durch unerwartete Plattform-Perturbationen während des Stehens), wurden bisher nur teilweise auf die biomechanischen Gütekriterien hin untersucht, wie etwa die Reliabilität. Aufgrund dieser Überlegungen basiert die vorliegende Dissertation auf fünf publizierten Studien, welche folgende Aspekte untersuchten: Wird die plantare Sensibilität durch verschiedene Körperpositionen während der Datenaufnahme beeinflusst (Studie 1)? Wie können plantare Sensibilitätsdaten angemessen analysiert werden (Studie 2)? Darüber hinaus wurde ebenso untersucht, inwiefern das sogenannte 'Posturomed'-Messgerät bei der Beurteilung dynamischer Gleichgewichtsantworten reliable Messwerte liefert (Studie 3). Ferner wurde in Studie 4 untersucht, inwiefern isoliert plantare Inputsignale bei Gleichgewichtsantworten relevant sind (anhand einer akuten sensorischen Manipulation, welche ausschließlich die Fußsohle betrifft). In Studie 5 werden konkrete klinische Anwendungsbeispiele aufgrund der vier hier vorgestellten Studien aufgezeigt. Die Hauptergebnisse der ersten vier Studien können wie folgt zusammengefasst werden: Erstens, höhere vertikale Kontaktkräfte während des Stehens verglichen mit sitzenden Positionen führten zu keinen Unterschieden bzgl. der plantaren Sensibilität. Dies ist eine wichtige Erkenntnis, da plantare Sensorikmessungen (oft während des Sitzens durchgeführt) dadurch in Kontext mit Gleichgewichtstests gebracht werden können, welche normalerweise im Stehen erfolgen. Zweitens, Daten der plantaren Sensorik zeigten Heteroskedastizität, was bedeutet, dass sich der Messfehler mit Größenzunahme der Messwerte ebenso erhöht. Wir konnten in Studie 2 ein leicht zu erschließendes Beispiel aufzeigen, wie das Problem der Heteroskedastizität durch eine Logarithmierung der Rohdaten behandelt werden konnte und wie kontrolliert werden konnte, ob diese Behandlung erfolgreich war. Drittens, die dynamischen Gleichgewichtsantworten, welche mittels des 'Posturomed' ermittelt wurden, zeigen insgesamt eine gute Reliabilität. Gelegentlich auftretende signifikante Unterschiede wurden anhand von Berechnungen der Wurzel der mittleren Fehlerquadratsumme (root mean square error, RMSE) als klinisch nicht relevant eingestuft. Viertens, eine anhaltende plantar-sensorische Manipulation (Hypothermie) wurde erfolgreich eingeleitet und während der Datenerhebung aufrecht erhalten. Studie 4 zeigte ferner, dass die hypothermisch eingeleiteten reduzierten plantaren Sensorik-Inputs während der eher nicht herausfordernden quasi-statischen Gleichgewichtsbedingungen (einfaches aufrechtes Stehen) kompensiert werden konnten. Während der herausfordernden Gleichgewichtskonditionen (unerwartete Perturbationen der Plattform während des Stehens) hingegen wurde keine vollständige Kompensation erreicht. Allerdings reagierten die Probanden mit einem vorsichtigen motorischen Verhalten. Dies wurde durch die reduzierten Ergebnisparameter infolge der plantaren hypothermischen Manipulation ersichtlich. Die vier hier genannten Studien zeigen weitere Erkenntnisse in Bezug auf Forschungsaktivitäten, welche sensorische und motorische Tests vereinen. Dies trifft speziell in Hinblick auf physiologische und methodologische Aspekte zu, welche bei der Analyse und Interpretation derartiger Daten in Betracht gezogen werden sollten. Zuletzt bietet diese Arbeit auch ein Beispiel dafür, welche klinischen Anwendungsfelder im Bereich der sensorisch-fokussierten Forschung identifiziert werden können. In Studie 5 wird dafür die Bedeutung sensorischer Forschung bei der (Früh-) Diagnose von Erkrankungen aufgezeigt, welche mit kognitiven Einschränkungen in Verbindung gebracht werden. Für diesen Zweck werden verschiedene Instrumente eingebracht, wie etwa sensorische oder koordinativ-motorische Tests. Vorläufige Ergebnisse deuten dabei bereits an, dass nicht nur die klassischen kognitiven Parameter und Fragebögen bei der Identifizierung oder zum Zwecke des besseren Verstehens kognitiven Verfalls einbezogen werden sollten

Effects of cervical muscle fatigue protocol on balance and field-dependency

Cervical functional capacity outcome measures that are simple and reliable are urgently needed in order permit accurate assessment/reassessment during treatments and rehabilitation. Induced neck muscle fatigue has been shown to alter functional capacities such as balance and kinaesthetic sense in the standing posture.A series of experiments were carried out in order to improve our general knowledge of neck functional capacities with the view to ultimately developing neck injuries management outcomes measures. In particular, the following questions were addressed 1) which optimal type of foam pads used during static computerised posturography are the most effective to enhance postural disturbances according each participant‟s weight and 2) what are the effects of various neck muscle groups fatigue on balance and on the perception of the subjective visual vertical and horizontal?The results suggest that the foam pads selected for posturography should 1) possess a sufficiently high modulus of elasticity and 2) result in minimal deflection under the participant‟s load. Additionally, this thesis highlights the role of different muscle groups on functional capacities. Firstly, neck flexor and extensor muscle groups do not appear to play as much a significant role in our space awareness abilities as initially thought. Secondly, extensors and lateral flexor muscle groups appear to be major contributing factors to cervical functional capacities.The novel approach used in this project provides results that challenge existing concepts on the role of different muscle groups on function. The new knowledge presented should help researchers in their development of more accurate and practical functional capacity testing protocol

Comparison of Balance Variables Across Active and Retired Athletes and Age Matched Controls

International Journal of Exercise Science 14(3): 76-92, 2021. Postural control is a major falls risk factor, therefore identifying protective mechanisms is essential. Physical activity enhances postural stability but effect duration has been minimally researched. The current study investigated if prolonged early life training exposure protected neuromuscular balance processes later in life. Static and dynamic balance variables were assessed in 77 healthy adults. Two age ranges (18 - 35yr, young; \u3e 50yr, retired) were divided into weight bearing athlete and control groups; young athlete (YA), young control (YC), retired athlete (RA) and retired control (RC). Static balance was quantified using force platform derived sway velocity (mm.s-1) and C90area (mm2) data (stable and unstable surfaces, eyes open and closed) Dynamic balance was assessed using the Y balance test (YBT). Results demonstrated significant age effect across groups. However, an athletic effect was evident only assessing dynamic balance and static time to error variables. Mean time to error data (YA, 27.8 ± 5.8; YC, 20.5 ± 11.1; RA, 9.4 ± 8.5; RC, 8.6 ± 9.1 s) recorded significant age and athletic effects for the most challenging condition completed (single leg stance, eyes closed, stable surface). Mean maximum YBT composite score (YA, 90.0 ± 5.4%; YC, 83.6 ± 6.5%; RA, 80.8 ± 10.7%; RC, 72.4 ± 15.5%) demonstrated an age effect, and also identified a group effect in the retired cohorts. The current study supports research highlighting declined balance with ageing. Overall, former athleticism did not significantly enhance static balance in later life. Dynamic balance incorporates muscle strength possibly inferring a protective role in former athletes

The Effect of Military Load Carriage on Postural Sway, Forward Trunk Lean, and Pelvic Girdle Motion

International Journal of Exercise Science 10(1): 25-36, 2017. Musculoskeletal injuries are a common occurrence in military service members. It is believed that the load carried by the service member impedes stability and alters back and pelvis kinematics, increasing their susceptibility to musculoskeletal injuries, specifically in the lower extremities. The purpose of this study was to examine the effects of two different loads on postural sway, forward trunk lean, and pelvic girdle motion in United States Army Cadets. Twenty male Army Reserve Officers’ Training Corps Cadets participated in this study. Each participant performed the Modified Clinical Testing of Sensory Interaction (mCTSIB) Protocol and the Unilateral Stance (ULS) Protocol under three different rucksack load conditions (unloaded, 16.0 kg, and 20.5 kg loads). Mean postural sway velocity was recorded along with 2-D kinematics of the trunk in the sagittal plane and the pelvis in the frontal and sagittal planes. External loads of 16.0 kg (p \u3c 0.001) and 20.5 kg (p ≤ 0.003) significantly increased mean sway velocity by 16% to 52% depending on stance and visual condition, but did not produce significant changes in trunk and pelvic kinematics

The test-retest reliability of centre of pressure measures in bipedal static task conditions - A systematic review of the literature

Summary of background data: The analysis of centre of pressure (COP) excursions is used as an index of postural stability in standing. Conflicting data have been reported over the past 20 years regarding the reliability of COP measures and no standard procedure for COP measure use in study design has been established. Search methods: Six online databases (January 1980 to February 2009) were systematically searched followed by a manual search of retrieved papers. Results: Thirty-two papers met the inclusion criteria. The majority of the papers (26/32, 81.3%) demonstrated acceptable reliability. While COP mean velocity (mVel) demonstrated variable but generally good reliability throughout the different studies (r= 0.32-0.94), no single measurement of COP appeared significantly more reliable than the others. Regarding data acquisition duration, a minimum of 90 s is required to reach acceptable reliability for most COP parameters. This review further suggests that while eyes closed readings may show slightly higher reliability coefficients, both eyes open and closed setups allow acceptable readings under the described conditions (r≥0.75). Also averaging the results of three to five repetitions on firm surface is necessary to obtain acceptable reliability. A sampling frequency of 100. Hz with a cut-off frequency of 10. Hz is also recommended. No final conclusion regarding the feet position could be reached. Conclusions: The studies reviewed show that bipedal static COP measures may be used as a reliable tool for investigating general postural stability and balance performance under specific conditions. Recommendations for maximizing the reliability of COP data are provided

Reliability of the Dynamic Gait Index in Vestibular Disorders

The purpose of this study was to examine the inter-rater and intra-rater reliability of the Dynamic Gait Index (DGI) when used with patients with vestibular disorders. Subjects included 30 patients aged 27-88 years, with vestibular disorders, who were referred for vestibular rehabilitation. Subjects\u27 performance on the DGI was concurrently rated by two physical therapists experienced in vestibular rehabilitation to determine inter-rater reliability. To determine intra-rater reliability each subject repeated the DGI one-hour later. Percent agreement and kappa statistics were calculated for individual DGI items. Kappa statistics for individual items were averaged to yield a composite kappa score of the DGI. Total DGI scores were evaluated for inter-rater and intra-rater reliability using Spearman rank order correlation coefficient. Inter-rater reliability of individual DGI items varied from poor to excellent based on kappa values. Composite kappa values demonstrated good overall inter-rater reliability of total DGI scores. Spearman Rho demonstrated excellent correlation between total DGI scores of both raters. Intra-rater reliability of individual items varied from fair to excellent based on kappa values. Composite kappa values demonstrated good overall intra-rater reliability of DGI. Fair but significant correlation was demonstrated between total DGI scores using Spearman Rho. It was concluded that the Dynamic Gait Index demonstrated only fair inter- and intra-rater reliability when used with subjects with vestibular disorders