EFFECTS OF BALANCE TRAINING IN ELDERLY EVALUATED BY CLINICAL TESTS AND DYNAMIC POSTUROGRAPHY

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1 Journal of Vestibular Research, Vol. 1, pp , 1990/91 Printed in the USA. All rights reserved $ Copyright 1991 Pergamon Press pic EFFECTS OF BALANCE TRAINING IN ELDERLY EVALUATED BY CLINICAL TESTS AND DYNAMIC POSTUROGRAPHY T. Ledin,* A. C. Kronhed,t C. Molier,* M. Molier,t L. M. Odkvist,* and B. Olssont *Department of Oto-Rhino-Laryngology, University Hospital, Link6ping and tdepartment of Research and Development in Primary Health Care, Mj6lby, Sweden Reprint address: T. Ledin, Dept. of ENT, University Hospital, Link6ping, Sweden o Abstract - All persons aged 70 through 75 years (N = 457) in a Swedish community were invited to participate in a 9 week balance training study. Out of 55 interested subjects, 15 were chosen at random for a study group; 15 matched controls were also selected. Before and after the investigation period the balance function was assessed by clinical balance tests and dynamic posturography. In the clinical balance tests, the training group significantly improved their balance standing on -one leg with eyes closed as well as standing on one leg while shaking the head; they also walked 15 m back and forth faster. In the dynamic posturography the training group significantly improved their equilibrium scores in the 3 most difficult test conditions. The results of the control group were unchanged except for one test condition in the dynamic posturography. The differences in one-leg standing with head shaking, walking 2 x 15 m, and the equilibrium score using sway-referenced platform in dynamic posturography were proved to be attributable to the training. The first investigation in all 29 subjects formed normative dynamic posturography data for the age group 70 through 75 years. The normative posturographic data of this age group differed from previously obtained data in the age groups 20 through 59 and 60 through 6~ years. It is concluded that elderly may improve their balance by regular balance training exercises for as short a period as 9 weeks. This might prove to be of great value in improving balance and thereby preventing accidental falls and subsequent fractures in elderly. o Keywords - dynamic posturography; training effects; aging; equilibrium. Introduction The incidence of hip fractures is steadily increasing among elderly, being approximately doubled during recent decades in Sweden (1). The incidence of hip fractures is probably associated with the frequency of falling among elderly. Gryfe et al (2) report that 60/0 of falls in an elderly population result in fractures and that 1 % are fractures of the hip. Patients with radial bone fractures have been postulated to display impaired postural equilibrium compared to controls (3), and a prospective study found impaired equilibrium in subjects who fell during the subsequent year compared to those who did not (4). The subjective ability to keep good equilibrium is markedly reduced in elderly about 65 years and older, according to questionnaires directed to the average citizen in both the USA (5) and Sweden (6). Other important factors to consider in assessing postural equilibrium are medication and social conditions (7). With aging there seems to be a loss of cells in both the peripheral and the central part of the vestibular system (8,9). The elderly have for practical and psychological reasons diminished drives for active body movements. These two factors might significantly contribute to decreased performance in tasks that demand postural reactions. It is also well known that central compensation after vestibular disturbances is delayed and in some cases less effective in elderly people (10). The decrease of RECEIVED 12 January 1990; REVISION RECEIVED 25 May 1990; ACCEPTED 28 May

2 130 vestibular function and nerve cells seems to accelerate around the age of 70 years (6,8,9). In order to remain in standing equilibrium, postural muscles generate acceleration forces acting on the body segments. The cerebellum and the brainstem integrate signals from the somatosensory, visual, and vestibular systems and correct equilibrium disturbances. These three systems all contribute to the postural control, and damage to any of them, or to the brainstem/cerebellum. will influence the overall output of the postural system. This has been studied using various forms of static posturography to assess body equilibrium (11-15). The dynamic posturography introduces new aspects of balance testing, in that not only the sway of the subject under stable conditions can be detected, but also external disturbances as well as distorted sensory influx can be provided. To accomplish this, the visual surround and the support platform can be stable or sway-referenced and the platform can be actively moved. In this way the different inputs to the postural system may to some extent be tested separately and more accurately. A sensory orgapization part of the dynamic posturography procedure tests the integration of sensory inputs to the equilibrium system; furthermore the movement coordination part, involving active platform movements, introduces a new dimension to the test dynamics in that the response of the equilibrium system to external disturbances may be studied. The influence of aging as measured by procedures similar to the dynamic posturography has been studied by Woollacott et al (16) and Manchester et al (17). Both studies found deteriorated balance function in the elderly compared to younger subjects in tests with sway-referenced support surface or visual surround, that is, when the proprioceptive and/or visual cues were not reliable. Furthermore, using electromyography the sequencing of muscular activity in response to active movements of the support surface was found to be disturbed in the elderly. Balance training studies are scarce. Young healthy subjects were studied by Brandt et al (18) during neck extension when balancing on a platform with eyes closed. The length of the T. Ledin et al training was 1 h a day for 5 days. They found daily improvements during the training hour as well as a downward trend in sway measures, ending at to 50% decrement after 5 days. Regarding the elderly, a previous balance training study demonstrated ambiguous results on static equilibrium parameters in healthy women above 65 years of age (19). Using a very short measurement period (up to 10 seconds), no effects of training were found in double leg stance. in single limb stance a small improvement in eyes open balancing capacity appeared, however it was not significant. On the other hand, a significant effect with eyes closed was found, paradoxically in favor of the control subjects. It has been postulated (20) that training might induce better stability and decrease the incidence of fractures in the elderly. Physical exercises expose the vestibular, visual, and somatosensory systems to new challenges and thereby enhance central nervous system balancing mechanisms. In addition, physical exercises have been shown to increase the bone mass in postmenopausal women (21), having yet another positive effect on fracture risk, as elderly also often suffer from osteoporosis. Thus, a study was designed to examine the effects of short-term balance training in a group of healthy elderly volunteers aged 70 through 75 years by applying physical exercises. Assessment of balance by means of clinical balance tests and dynamic posturography was used as a more sophisticated testing of equilibrium performance than static measures of balance only, thus better resembling the dynamic disturbances of balance during daily life activities. Furthermore, as no dynamic posturography data is available for normal subjects above 70 years of age, comparisons between all subjects prior to the investigation period and previously obtained normal values in the age ranges 20 through 59 and 60 through 69 years were made. Materials and Methods From the Swedish population register in the county of Vadstena (total population

3 Equilibriometric Effects of Balance Training in Elderly ), all persons of ages 70 through 75 years were retrieved (N = 457). Of these, 30 were immediately excluded due to known handicaps or diseases (for example, dementia and hospitalization). The remaining subjects (427) were invited to participate, and informed that participation required independence of walking aids indoors. A total of 55 subjects replied. These were arranged in random order and contacted sequentially by telephone to set up a group of 15 subjects participating in the training program during 9 weeks, with exercises twice a week. Exclusion criteria were severe vertigo, epilepsy, Parkinson's disease, stroke, rheumatoid arthritis, total hip replacement, severe heart disease, severe hypertension, and abuse of alcohol. Persons taking drugs supposedly affecting the equilibrium performance (for example, sedatives and anxiolytics) were also excluded. Among the remaining subjects who had announced their interest to participate, a control group was selected that should match the training group according to age, sex, smoking, alcohol and physical activity habits. This group was instructed to continue their life style as before during the investigation period. One person in the control group did not participate in the dynamic posturography and was therefore excluded from the analysis. Thus the training group consisted of 8 women and 7 men with mean age 73.2 years (SD 1.5 years) and the control group of 7 women and 7 men with a mean age of 72.7 years (SD 1.6 years). The training program was performed twice a week during 9 weeks. Exercises were conducted by an experienced physiotherapist and carried out for 45 minutes followed by 10 to 15 minutes of muscle relaxation. The training program was particularly designed for the study and contained general gymnastic and balance exercises including parts of the vestibular habituation program developed by Norre and de Weerdt (22). It included the following tasks: jogging and jumping walking straight forward, backward, on toes and heels walking with sudden turns of and walking sideways rising from sitting standing on one leg with eyes open and closed visual fixation during neck flexion, torsion, and lateral flexion exercises playing with balls (for example, throwing, catching, and bouncing) jumping exercises on a trampoline The test procedure included both clinical balance tests and dynamic posturography. The clinical tests were performed 14 days before the training period and 7 days after the training sessions. The dynamic posturography was performed 7 days before and 5 days after the training sessions were ended. Balance Test Protocol Measurements of the time a subject can stand without losing balance (maximum 30 seconds) were made during the following conditions: feet together with eyes open and closed (Romberg test) tandem feet with eyes open and closed (sharpened Romberg test) standing on one leg with eyes open and closed (best leg is counted) both feet together while shaking the head with eyes open standing on one leg while shaking the head with eyes open (best leg is counted) iv.ieasuremem of walking speeci. the time required to walk back and forth 15 meters x 2 including turning Qualitative measurements of the presence or absence of corrective/erroneous steps in some maneuvers: turning to left and right walking toe to heel 15 steps backward between two lines walking heel to toe 15 steps forward on a line.

4 132 In total, 12 clinical tests were conducted. Each test was performed 3 times with registration of the best trial, except for the walking speed and turn around tests, which were conducted only once. Dynamic posturography (EquiTest, Neurocom Int Inc, Clackamas, Oregon, USA) was performed as described by NashTler (23) and Cyr et al (24). In the dynamic posturography, which was performed in the standard prea dual forceplale enclosed by a visual surround. Both the forceplate and the surround can be made to move with the person's anteroposterior (AP) sway or independent of the sway, thus enabling programmed disturbances of the equilibrium. The dual forceplate records the vertical forces between feet and ground as well as shear forces, thereby allowing estimation of the position of the swaying body as well as the pattern of sway in terms of hip or ankle strategy. The investigation is divided into two main sections: sensory organization test (SO) and movement coordination test (MC). The fundamentals of the SO part are thoroughly described by Black et al (25) and those of the Me part by Diener et al (26). The SO part is T. Ledin et al divided into 6 separate tests (Figure 1), lasting 20 sec each with test 4, 5, and 6 repeated three times. SO 1 is a quantified version of Rombergs test. The subject stands with eyes open and the surrounding as well as the ground are stable. SO 2 is equal to SO 1 except that the eyes are closed. In SO 3, performed with eyes open, the visual surround moves in response to the body sway. In test SO 4 the platform is sway-referenced and the surrounding stable.!!! test SO 5. with eves closed, the platform is sway-referenced, and in test SO 6 both the platform and surrounding are sway-referenced. Note that in SO 3 and SO 6 the tested subject might have some orientation information from the surrounding as it is only moving in the AP direction and not in the lateral direction. From each test an equilibrium score is computed. The score is 100 for absolutely no sway, decreasing with increasing sway range during the 20 sec measurement time, and zero in case of 12.5 sway range, or falling. A strategy score, related to the amount of shear force exerted, is computed expressing the degree.of ankle or hip movements - the more shear force the more of hip movements. A strategy score of 100 means solely ankle and z o - l- e z o U l- 1 e:: Q. ~ ~ Q. ~ w 4 ~ ~~ ~ VISUAL CONDITION FIXED EYES CLOSED 2 5 SWAY REFERENCED 3 6 Figure 1. The six different sensory conditions of dynamic posturography.

5 Equilibriometric Effects of Balance Training in Elderly 133 no hip movements, and zero corresponds to a horizontal shear force of about 110 N. Alignment data, that is, the angle between body and earth vertical, is also calculated during the trial. Initial alignment describes the conditions before the start of each test, and dynamic alignment is the angle during the test. The MC part is divided into 8 separate tests: small, medium and large backward and forward translation perturbations of the platform, to simulate falling forward and backward, are repeated 3 times each, and furthermore the platform is tilted toes-down and toes-up 5 times each. From the translation perturbations, the force response of each foot is evaluated to yield force symmetry scores between right and left foot. The slope and latency of force recruitment for each foot are also assessed to give estimations of the reaction of each foot separately. The average values of both feet are used in the analysis. A strategy score is also used in the MC part to estimate the degree of hip compared with ankle strategies. Finally the toes-up and toes-down tiltings are evaluated to estimate the adaptation in terms of decreasing energy required to correct the disturbance. The equilibrium scores of the 29 subjects prior to the investigation period were compared to the normative data for younger age groups, which was supplied by Neurocom Int Inc. These data were means and standard deviations of 112 subjects of ages 20 through 59 years and 20 subjects of ages 60 through 69 years. Statistical Analysis Student's t test between groups was used for comparison of all 29 subjects before the investigation period to the normative data in younger age groups. Wilcoxon's rank sum test was used to evaluate the presence of any differences between the training and control groups prior to training and the effects attributable to the training, which were measured as the differences between the training and the control groups regarding each subject's difference prior to the investigation compared to after. The test results prior to and at the end of the investigation period, in each group, were also evaluated with Wilcoxon's paired rank sum test to measure the effect of the investigation period for each group separately. In the dichotomous variables from the balance protocol (absence or presence of corrective steps), the sign test was used. Significance levels below 5070 were considered significant. Results Comparisons of equilibrium scores of all 29 subjects prior to the investigation period and the younger normative data supplied by Neurocom Int Inc are displayed in Table 1. Significant differences were found between the group of 70 through 75 year olds compared to the 60 through 69 year olds in conditions SO 3 (p < 0.05) and SO 5 (P < 0.01). When comparing to the 20 through 59 year olds, highly significant differences (P < 0.001) occurred in all conditions except SO 1 and SO 4. No significant differences in the balance tests or in the dynamic posturography, neither the SO nor the MC part, could be found between the training and control groups prior to the training period. The average participation in the training sessions was 16 times out of a possible 18. In the control group, the subjects gained an average of 0.8 kilograms of weight during the investigation period (P < 0.05), whereas i~!he t r 2jning gr01j~ ~!1~ suqje~~~ 10s~ c:: 2Yerage of 0.8 kilograms (P < 0.05). The effects of training are summarized in Table 2 (balance tests), Table 3 (SO part of dynamic posturography), and Table 4 (Me part of dynamic posturography). When comparing the differences for each subject between the groups to estimate the effects of the training, significant differences were found when standing on one leg with eyes open and head shaking (P < 0.001), and walking 15 m x 2 including turning around (P < 0.05). In the dynamic posturography SO tests, a significant

6 134 T. Ledin et al Table 1. Comparison of Equilibrium Score Averages in the SO Part of Dynamic Posturography in 3 Age Groups. (Left significance values refer to comparisons between the two oldest groups, right values compare 70 through 75 year olds to 20 through 59 year olds.) years years years (n = 112) (n = 20) (n = 29) Condition mean SO mean SO mean SO P P SO SO SO SO SO SO 6 FJF) The 20 through 59 and 60 through 69 years data are supplied by Neurocom Int Inc. = not significant. 'P<0.05, ' P<0.01, P< difference was found in condition SO 4 (sway-referenced platform, P < 0.05). Both training effects and value of prior knowledge of the tests were measured. The effects of the investigation period in each group separately were as follows: The training group showed significant improvements in the balance tests when stand- Table 2. Table of Preinvestigation and Postinvestigation Period Values (means and standard deviations) in the Balance Tests. Significance values for comparisons between before and after the investigation period within each group and estimation of the effects attributable to the training (rightmost column) are given. Units of measure are given next to each item. Training Group (n = 15) Control Group (n = 14) Net Before After Before After Effect Clinical tests Condition x SO x SO p x SO x SO p P Romberg eyes open (s) eyes closed (s) Sharpened Romberg eyes open (s) eyes closed (s) One leg stance eyes open (s) eyes closed (s) Two legs stance shaking head (s) One leg stance shaking head (s) Walking x 15 m (s) Turning 360 degrees left/right (subjects using corrective steps in any direction) 2/15 1/15 Walking 15 steps backwards 2/14 2/14 (subjects using corrective steps) 4/15 4/15 Walking 15 steps forwards 7/14 7/14 (subjects using corrective steps) 3/15 1/15 3/14 8/14 = not significant. P<0.05, P<0.01, P<O.OO1.

7 Equilibriometric Effects of Balance Training in Elderly 135 Table 3. Preinvestigation and Postinvestigation Period Values (means and standard deviations) in the SO Part of Dynamic Posturography (Statistical Comparisons as in Table 2) Before Training Group (n = 15) After Condition x SO x SO p Equilibrium scores SO SO SO S SO SO Strategies SO SO S S SO SO Control Group (n = 14) Net Before After Effect x SO x SO p P = not significant. 'p < 0.05, P < ing on one leg with eyes closed (P <. 0.05), standing on one leg while shaking the head (P < 0.01), and walking back and forth 15 meters X 2 including turning around (P < 0.01). In the SO part of dynamic posturography the equilibrium scores in test conditions SO 4-6 (all conditions with sway-referenced platform) increased significantly (P < 0.01 in all cases). In the Me test the latencies of the training gr6up decreased significantly in the large backward perturbations (P < 0.05). In the control group the equilibrium scores in the SO part of dynamic posturography in most SO test conditions showed no differences. However, a significant increase in condition SO 5 (sway-referenced platform and absent vision) was found (P < 0.05). For variables (both balance tests and dy- Table 4. Table of Preinvestigation and Postinvestigation Period Values (means and standard deviations) in the Me Part of Dynamic Posturography (latencies are given in ms; statistical comparisons as in Table 2) Motor response latencies... :::" Training Grou;: (.r =0 :'::Jllt!'V; 3ruup ~J; =-,..., ~, Net Before After Before After Effect Condition x SO x SO p x SO x SO p P Backward perturbations Small Medium Large Forward perturbations Small Medium Large = not significant. 'p< 0.05.

8 136 namic posturography) not mentioned above, no significant effects were found. Discussion The present study was designed to assess the ability to train the postural system among elderly, which should be of importance in the handling of vertigo and balance disorders. The balance training as well as the evaluation comprised both stanc and aynamic procedures, thus covering a greater part of the situations in real life, where the elderly subject is exposed to hazards. Traditionally, estimations of balancing ability have often been limited to static measures of balance. The concept of balance training is at least threefold. The first part consists of an increase of the activity of the receptor organ in the inner ear during the exercises. This is achieved by head movements, preferably rotating accelerations in different directions stimulating the vestibular activity with increase of the afferent flow of action potentials. The second part is activating the integrating mechanisms in the e by offering varying proprioceptive, visual, and vestibular inflow. The third part constitutes training of the neuromuscular postural effector organ to handle different positions and movements, promoting coordination, minimizing sway, and preventing falls. The training effect seems to be mainly a C function, to a lesser degree concerning muscular strength as our training program was not directed towards muscle strength. Of course the mental effect, the psychological benefit from the training, may be important. The old person gets an increased confidence resulting in more effective movements. The training group as well as the controls were chosen using accepted match principles. Except for one dropout, the test persons participated well. It must be remembered, though, that participation required active interest from the subjects, thus they possibly constituted a physically or at least mentally somewhat selected group, compared to elderly in general. Comparing all 29 subjects prior to the in- T. Ledin et al vestigation with the normative data provided by Neurocom Int Inc revealed significant differences in most SO conditions when comparing the 70- through 75-year-old group with the 20- through 59-year-old group, and in a few conditions when comparing to the 60- through 69-year-old group. The reason for using Neurocom normative material was that this database is used by most EquiTest users and that the database seems sufficiently reliable in clinical practice. Albeit the normative data refers to an American population, the differences suggest that there is a decrease in balance performance around the age of 70 years, in agreement with other authors (6,27). In the balance tests, the Romberg tests with feet together and eyes open or closed did not demonstrate any significant training effect differences between groups, which is in accordance with Lichtenstein et al (19). Obviously these tests are not challenging the limits of stability, and healthy subjects at this age should be able to perform perfectly (that is, be able to stand at least 30 seconds) in these tests. Thus, a perfect Romberg test does not necessarily imply a good balance function. In dynamic posturography, the test conditions SO 1 through SO 3 in the SO test are the easiest, using stable support, and no significant differences were found between the groups. However, in test conditions SO 4 through SO 6, the balance system was more stressed with a sway-referenced platform (SO 4) and, in addition, vision excluded (SO 5) or distorted (SO 6), and highly significant improvements were found in the training group. Even in the control group, a significant difference was found in condition SO 5; furthermore, there was a lack of net training effect in condition SO 6. This is probably attributable to the fact that the control group, having an observed improvement in both tests, had experience of the test conditions, giving them better results, even significantly so in SO 5. The effect in the training group, comprising the sum of training effects and the experience of the testing conditions from the first measurement, was thus not large enough in either test SO 5 or SO 6 to produce a significant difference between the groups. Obviously, there is a drawback in using difficult tests in that

9 Equilibriometric Effects of Balance Training in Elderly 137 prior experience of the test may in some cases be as important as training effects, making the latter difficult to unveil. The reason for the improvements observed in the training group could thus be multifactorial. First, a general improvement of motor and sensory orientation functions could have occurred. Second, enhanced stability is followed by a lessened fear of falling. Third, if there was a general improvement in muscle strength, and possibly also due to the observed weight reduction, improvements in equilibrium scores in tests SO 4 through 6 could have occurred. Finally, it must be remembered, as outlined above, that prior experience of the testing conditions may be of importance. In the Me tests, no net effects attributable to training could be shown. This is in accordance with what was expected, as the latencies are merely monitors of the stretch reflexes, nerve impulse transmissions, and the time required to activate the muscular function to produce torque around the ankles. None of these processes are likely to improve by exercise. The reason for the single decrement of motor latency in one of the perturbations in the training group is obscure. It must be remembered, though, that some statistically significant results do arise by chance, and must be interpreted with great caution. The balance tests displaying significant improvement after training were those that were most difficult to perform, for example, standing on one leg with head shaking or on one leg with eyes closed, which consequently would stress the equilibrium ability to its limits. The finding of the overall poor performance ( 5 to 6 s standing time) when standing on one leg with eyes closed needs further attention. Normal elderly obviously have a significantly reduced performance compared to what one would by experience expect from younger subjects. Furthermore, the significant increase after the training, although small in the measured number of seconds, indicates that exercises, or perhaps prior memory of the test, indeed seem to cause improvement in difficult tests of equilibrium. When assessing possible vestibular dysfunction in elderly, comparison must always be made to normative data for the same age group. Also in walking back and forth including turning on time, the difference was significant in the training group. We firmly believe that this is a function of increased stability and spatial self-confidence. However, as the training program included items similar to this test, it is of course possible that the difference can be explained by specific training, and not due to general improvement of balancing capacity. Suominen et al (28) found significant increase in oxygen uptake and muscle metabolism after 8 weeks of strenuous exercises 3 to 5 hours a week in men 56 through 70 years of age. However, in our study the total training time was shorter, and the training was not directed towards increasing muscle strength. Thus, it is unlikely that the improvement is, in any considerable part, due to muscular strength increase, leaving enhanced central nervous system mechanisms as the most probable cause of improved balance performance. However, measurements of muscular strength is this study would have been preferred, but had to be discarded for practical reasons. Added together, these results indicate that even at ages over 70 years there is a plasticity and learning ability of the vestibular system and its central integration. This is in contrast with the ambiguous results of Lichtenstein et al (19), who studied the effects of exercises on static parameters in balance performance in women of ages above 65 years. However, their measurement procedures were different from this study, making it hazardous to compare the results. When testing balancing ability, static measures are often employed. In this study we have found that static measures of balance often fail to unveil differences. Thus, maybe dynamic measurements would be preferred. It is also important not to be satisfied with a standard vestibulooculomotor reflex investigation when assessing balance. The vestibulooculomotor system comprises just one of the parts in the complex process of remaining in stable equilibrium under different conditions. From this study it is concluded that regular balancing exercises that expose the visual, vestibular, and somatosensory systems and

10 138 the integration in the e to new challenges, in a very short time are able to achieve significant improvements in some aspects of balance function. If physical exercises could be implemented among the elderly, it would most certainly improve balance and general health and decrease the high incidence of fall- T. Ledin et al ing and subsequent fractures in the growing population of elderly. Acknowledgments-The technical assistance in the dynamic posturography investigations by Mr 10- han Deblen and Mrs Lisbeth Noaksson is gratefully acknowledged. REFERENCES 1. 10hnell 0, Nilsson S, Obram K, Sernbo L Age ana sex pattern of hip fractures - changes in 30 years. Acta Orthop Scand. 1984;55: Gryfe Cl, Amies A, Ashley MJ. A longitudinal study of falls in an elderly population; 1: incidence and morbidity. Age Ageing. 1977;6: Ring C, Nayak L, Isaacs B. Balance function in elderly people who have and who have not fallen. Arch Phys Med Rehabil. 1988;69: Fernie GR, Gryfe CI, Holliday PJ, Llewellyn A. The relationship of postural sway in standing to the incidence of falls in geriatric subjects. Age Ageing. 1982;11: Gerson LW, Jarjoura D, McCord G. Risk of imbalance in elderly people with impaired hearing or vision. Age Ageing. 1989;18: Odkvist LM, Malmberg L, Moller C. Age-related vertigo and balance disorders according to a multiquestionnaire. In: Claussen CF, Kirtane MV, Schlitter K, Eds. Vertigo, nausea, tinnitus ang hypoacusia in metabolic disorders. Amsterdam: Elsevier Science Publishers B. V. 1988; Wickham C, Cooper C, Margetts BM, Barker DJP. Muscle strength, activity, housing, and the risk of falls in elderly people. Age Ageing. 1989;18: Rosenhall U. Degenerative pattern in the aging human vestibular neuro-epithelia. Acta Otolaryngol (Stockh). 1973;76: Bergstrom B. Morphology of the vestibular nerve; 2: the number of myelinated vestibular fibers in man at various ages. Acta Otolaryngol (Stockh). 1973;76: Norre ME, Beckers A. Benign paroxysmal positional vertigo in the elderly: treatment by habituation exercises. J Am Geriat Soc. 1988;36: Diener HC, Dichgans J, Bacher M, Gomph B. Quantification of postural sway in normals and patients with cerebellar disease. Electroencephalog Clin Neurophysiol. 1984;57: Dichgans J, Mauritz KH, Allum JH, Brandt T. Postural sway in normals and atactic patients: analysis of the stabilizing and destabilizing effects of vision. Agressologie. 1976;17: Kapteyn TS. Data processing of posturographic curves. Agressologie. 1972; 13(suppl B): Ledin T, Tropp H, Odenrick P, Odkvist LM. Postural sway and corrections. In: CF Claussen, MV Kirtane, Eds. Vertigo, nausea, tinnitus and hearing loss in cardio-vascular diseases. Excerpta Medica International Congress Series 708, 1986; Ledin T. Odkyist LN!, Moller C. Posturography findings in workers exposed to industrial solvents. Acta Otolaryngol (Stockh). 1989;107: Woollacott MH, Shumway-Cook A, Nashner LM. Aging and posture control: changes in sensory organization and muscular coordination. Int J Aging Hum Dey. 1986;23: Manchester D, Woollacott M, Zederbauer-Hylton N, Marin O. Visual, vestibular and somatosensory contributions to balance in the older adult. J of Gerontol. 1989;44:M Brandt, T, Krafzcyk S, Malsbenden 1. Postural imbalance with head extension: improvement by training as a model for ataxia therapy. Ann NY Acad Sci. 1981;374: Lichtenstein MJ, Shields SL, Shiavi RG, Burger MC. Exercise and balance in aged women; a pilot controlled clinical trial. Arch Phys Med Rehabil. 1989;70: Overstall PW. Prevention of falls in the elderly. JAm Geriatr Soc. 1980;28: Chow R, Harrison JE, Notarius C. Effect of two randomised exercise programmes on bone mass of healthy postmenopausal women. Br Med J 1987;245: Norre ME, de Weerdt W. Treatment of vertigo based on habituation. J Laryngol Otol. 1980;94: Nashner LM. A systems approach to understanding and assessing orientation and balance disorders. Advances in diagnosis and management of balance disorders conference, Boston, Massachusetts, Oct 1987 (available from Neurocom Int Inc, Clackamas, OR, USA). 24. Cyr DG, Moore GF, Moller CG. Clinical application of computerized dynamic posturography. Ear Nose Throat J (supp!). 1988;9: Black FO, Wall C III, Nashner LM. Effects ofyisual and support surface orientation references upon postural control in vestibular deficient subjects. Acta Otolaryngol (Stockh). 1983;95: Diener HC, Horak FB, Nashner LM. Influence of stimulus parameters on human postural responses. J Neurophysiol. 1988;59: Overstall PW, Exton-Smith AN, Imms FJ, 10hnsson AL. Falls in the elderly related to postural imbalance. BR Med J. 1977;1: Suominen H, Heikinen E, Liesen H, Michel D, Hollman W. Effects of 8 weeks' endurance training on skeletal muscle metabolism in year-old sedentary men. Eur 1 Appl Physio!. 1977;37: