Image shows testing of subject with posturogràphy instrument (Smart Balance Master^). Photograph by Don Larson, Medical Education Resources Program, Indiana University, Indianapolis, Indiana.
The concept of frailty is becoming more prominent in gerontological literature partially because frailty is more predictive of mortality and nursing home use than medical diagnoses and age (Winograd et al., 1991). Frailty, defined as decreased functioning combined with diminished self-rated health (Rockwood, Fox, Stolee, Robertson, & Beattie, 1994), has been associated with physical and cognitive dysfunction, falls, morbidity, institutionalization, and mortality (Guralnik & Simonsick, 1993). Preventing frailty through an understanding of the physiologic basis of the condition is an important research undertaking. Findings may lead to specific clinical assessments to identify frail individuals, and interventions can be developed to prevent or minimize the condition. Such interventions could enhance active lives in older adults and decrease health care costs to society (Büchner & Wagner, 1992; Pendergast, Fisher, & Calkins, 1993; Rockwood et al., 1994).
Preventing and treating frailty are important concerns for older adults, their families, and society because when people reach age 65, they can expect to live at least another 20 years (Hodes, 1994). It is estimated that by the year 2020, 60 million people will be 65 years of age or older, with those older than age 85 increasing to an estimated 13 million by 2040. The 85 years and older group comprises the most frail segment of the population (Bowsher, Bramlett, Burnside, & Gueldner, 1993). Expenditures for health and long-term care needs were $215 billion in 1990, and a considerable portion of that money went to the care of frail older adults (Torres- Gil, 1990). Because of the increasing number of older adults, the cost of frailty will continue to grow if treatments to prevent or remediate frailty are not identified.
More than 20 variables are cited in the literature describing frail people, but there is little consensus about which variables discriminate between frail and nonfrail older community-residing adults, especially variables that may be amenable to interventions (Bortz, 1993; Brown, Renwick, & Raphael, 1995; Rockwood et al., 1994). There are a number of older adults who have chronic illnesses and problems with mobility, but those individuals may not be considered by others or themselves as frail.
Brown et al. (1995) defined frailty as the diminished ability to do important practical and social activities of daily living (ADLs) coupled with the meaning the person places on the disability, i.e., perceiving that a decrease in functioning signals a decline in health. It is proposed that an older adult's perception of both a decline in functioning and a decline in health connotes frailty, whereas a positive self -rated health in the presence of functional decline offsets declines in functioning and indicates nonfrailty (Guralnik & Simonsick, 1993; Rockwood et al., 1994; Schulz & Williamson, 1993).
The purpose of this study was to develop empirically based criteria for differentiating between frail and nonfrail older adults using measurements of balance and muscle strength and age. Hadley, Ory, Suzman, and Weindruch (1993) suggest impairments of strength and balance may be important contributors to frailty. The ability to balance within varying environmental conditions and the presence of sufficient muscle strength to move within varying environments are fundamental to the performance of ADLs. However, there is little empirical evidence to support the hypothesized contributions of impairments in balance and muscle strength to frailty.
A systems model of balance and movement provides a framework for examining the contributions of impairments in balance and strength to frailty (Nashner, 1994; Woollacott, 1993). A systems model is based on the assumption that multiple neural and musculoskeletal factors contribute to balance. Three major factors include:
* Use of visual, somatosensory, and vestibular inputs for stability.
* Use of adaptive mechanisms to shift the dominant sensory input controlling stability.
DESCRIPTION OF SMART BALANCE MASTER' MEASUREMENT CONDITIONS
* Sufficient strength in the muscles controlling the ankle and knee used in the production of postural movements.
Automatic responses, or learned postural movement reflexes used in response to gravitational and environmental disturbances, assist people to maintain postural stability when standing balance is disturbed, such as when reaching for an object or when stumbling over an uneven support surface. Automatic responses control how much people sway around their centers of gravity. The manner in which the inputs from the visual, somatosensory, and vestibular senses converge and are organized within the subcortical areas of the brain is related to stability by influencing the timing, direction, and amplitude of corrective postural actions (Nashner, 1982). For example, if an older adult stands on a hard floor surface in a pair of well-supported shoes, and the room is well lighted, the sensations from the joint and tactile receptors in the feet and ankles, visual receptors, and vestibular organs should result in very small amounts of sway. If a person has a large amount of sway, the nurse could infer that the convergence and organization of information from the three senses is poor. Additionally, if an older adult stands on a compliant surface, such as a thick rug, and is wearing shoes with heavily padded soles, and the room is dark, the person may not be able to organize senses from the low visual inputs and compliant surface with inputs from the vestibular system, and the sway could become so large that the person falls. According to Woollacott (1993), in older adults with either diminished or absent visual inputs or reduced somatosensory inputs from joint and tactile receptors, balance is similar to that of younger adults under similar conditions. However, when both of these sensory inputs are reduced or absent, leaving vestibular inputs to primarily control stability, older adults' sway is increased, as compared to younger adults' sway, and they lose their balance under certain conditions.
The ability to select functionally appropriate sensory inputs when one or two inputs conflict with those remaining is important to maintaining stability under changing environmental conditions. For example, when riding an escalator or a moving walkway, an older adult may not be able to select the inputs from the somatosensory and vestibular receptors that inform the person they are standing still - functionally appropriate inputs - and instead focus on the visual inputs that arise from moving past walls or other cues in the environment.
Lastly, balance is influenced by strength in the muscles controlling the ankles and knees that are used in the production of postural movements and gait. Research has demonstrated a loss of strength in the lower extremities among some older adults (Woollacott, 1993). Of particular importance is that loss of strength in dorsiflexor muscles is associated with falls and difficulty performing certain ADLs. (Fiatarone & Evans, 1993; Tinetti, Speechley, & Ginter, 1988; Whipple, Wolf son, & Amerman, 1987). Decreased muscle strength is also associated with slower postural muscle response latencies of ankle dorsiflexors in older adults (Woollacott, 1993; Woollacott, Shumway-Cook, & Nashner, 1986).
The data for this study come from a larger study that examined the effects of two exercise interventions among community-residing older adults. All measurements reported in this study were taken prior to beginning the exercise interventions.
Subjects were recruited who met the inclusion criteria of 60 years of age or older, living independently in the community, able to speak and read English, and sufficient vision to read large print. Exclusion criteria included: diagnosis of neurological diseases, arthritis with severe pain that prevented activity, or presence of major symptoms suggestive of cardiopulmonary or metabolic disease unless physician approval was obtained (American College of Sports Medicine, 1995). Eighty-four people met the criteria for participation; each completed all measurements and were included in this analysis.
Potential subjects were recruited through announcements in a local senior services agency and newspapers. Older adults responding to advertisements were telephoned for an initial assessment to assure they met the criteria for participation in the study. Requirements for participating in the study were explained to potential participants, and they were invited to undergo testing after signing an informed consent prior to beginning the measurements.
Standard measurement procedures were followed during the assessments of balance and strength. Sufficient time was allowed during measurements of balance and strength to minimize fatigue. Most subjects completed the assessments within 1 hour.
Frailty. Frailty was measured by combining the self-reports of two measures, a measure of functional performance of ADLs using the World Health Organization Assessment of Functional Capacity (WHOAFC) (Ferrucci et al., 1991) and a self-report of perceived health. Using the combined measures is consistent with the previously described conceptual definition of frailty (Rockwood et al., 1994). The WHOAFC is a 14-item measure of self-sufficiency in the performance of basic and instrumental ADLs. Each item is scored on a 5point scale ranging from 1 (the respondent can perform the task without difficulty) to 5 (unable to perform) with intermediate values suggesting a need for varying levels of assistance. A sixth category is used for the respondent to indicate that the activity is not performed because of tradition or culture, suggesting that the item is not an important activity for the respondent. A score of 14 means complete self-sufficiency; 70 means total dependency. Internal consistency reliability for this sample was satisfactory (alpha .79).
CHARACTERISTICS OF SAMPLE BY GROUP
Perceived health was measured by one question: "In comparison with other people your age, how would you judge your state of health?" There were five possible responses: excellent, good, fair, poor, or terrible.
If respondents scored 20 points or less on the WHOAFC, with scores adjusted for items omitted because they were judged not to be important, and reported excellent or good health, they were categorized as nonfrail. A score of 20 or less suggested that the person could perform all activities without difficulty or that there were up to four activities the person could perform with difficulty but without help, two activities requiring partial help, or one activity requiring total help (e.g., cutting toenails) (Ferrucci et al., 1991). Consistent with the definition of frailty (Rockwood et al., 1994), subjects who had WHOAFC scores of 21 or more and a self-report of fair or poor were classified as frail. If the two measures were not in agreement, the subject was categorized as frail or nonfrail based on the subject's report of perceived health. Of the 84 subjects, there was disagreement between the WHOAFC score and perceived health for 6 subjects. The decision to use perceived health as the criteria for classification between frail and nonfrail even when the WHOAFC score was 21 or greater is consistent with the definition that disability alone does not constitute frailty unless the individual perceives those disabilities as influencing their health (Rockwood et al., 1994). This categorization of perceived health is consistent with that of Gregg, Kriska, Fox, and Cauley (1996).
Balance. A posturography instrument (Smart Balance Master®) (Neurocom International, Inc., 1993), shown on page 18, was used to measure automatic postural movements while the subject used visual, somatosensory, and vestibular inputs for postural stability. Automatic movements involve the coordination of leg and trunk muscles in response to conditions in which people are trying to maintain stability. Additionally, the instrument provides data to assess people's ability to ignore inaccurate visual or somatosensory input, either individually or in combination, and rely on remaining accurate inputs.
The instrument measures percent of stability during six measurement conditions (Table 1). The measurements assessed sensory organization of visual, vestibular, and somatosensory inputs under varying conditions, including eyes closed, moving floor surface, and moving visual surround (Nashner, 1990). Percent of stability scores are percentages comparing the subject's peak amplitude of anterior-posterior sway with theoretic limits of stability (Nashner, 1994). Scores approaching 100% suggest small sway amplitudes, whereas scores approaching 0% suggest large amplitudes. Each measurement condition from Condition No. 2 through Condition No. 6 altered the environment by either eliminating the visual input (eyes closed) individually or in combination with sway-referenced movement of the support surface (floor of the machine) or sway-referenced both the support surface and the visual surround (blue material tightly wrapped around three sides of the machine). Sway-referencing means that the orientation of the support surface or the visual surround or both remains constant in relation to the subject's center of gravity sway angles. Although both the somatosensory and visual systems are provided information during the sway-referenced conditions, information to the systems does not provide functionally useful information regarding orientation of the body's center of gravity to the vertical axis of the body (Nashner, 1994). For example, sway-referencing the floor may be similar to standing on a compliant surface, such as very soft carpet or sand. Information from swayreferenced inputs suggests to the individual that the orientation of the center of gravity is not changing, when in fact it is. If subjects lost their balance during a trial or moved their feet or grabbed the visual enclosure to prevent loss of balance, stability scores were assigned 0%. Intratrial correlations ranged from .73 to .85 for measurement Conditions 3, 4, 5, and 6, the conditions in which data were obtained during three trials, and then averaged to obtain one score (Wigglesworth, Dayhoff, & Suhrheinrich, 1994).
MEANS AND DIFFERENCES OF WORLD HEALTH ORGANIZATION ASSESSMENT OF FUNCTIONAL CAPACITY ITEMS BY GROUP
Muscle Strength. A hand -held dynamometer (Microfet®) (Hoggan Health Industries, 1991) was used to nssess the strength of the postural muscles of the lower leg. Three trials of maximum effort to perform knee extension, plantar flexion, and dorsiflexion were obtained. The peak force of the three trials was averaged to obtain an average strength score. Intratrial reliability has been reported to be .92 to .97 for dorsiflexion and plantar flexion, respectively, and test-retest reliability as .85 to .76, respectively (Topp & Mikesky, 1994).
Prior to performing a discriminant analysis, the correlation matrix was examined to evaluate for multicollinearity or whether or not the variables were highly interrelated, an undesirable characteristic for performing a discriminant analysis. Descriptive analysis of the WHOAFC items and a one-way univariate analysis were conducted to identify which individual items were significantly different between the two groups. A two-group stepwise discriminant analysis was then performed to identify if frail and nonfrail subjects were differentiated by the four balance measures, three strength measures, and age. A critical F statistic with an alpha value of .05 was used for classification of the predictor variables. A classification analysis was conducted to estimate the goodness of fit and the sensitivity and specificity of the model (Huberty & Barton, 1989; Tabachnick & Fidell, 1989).
Description of Subjects
Subjects' ages ranged from 60 to 88; 86% were females. All lived independently in the community, either alone or with spouses or friends. Most had one or more chronic diseases; the most commonIy reported diseases were diabetes, cardiac, pulmonary, and arthritis. Fifteen (18%) were classified as frail using the criteria described above. Neither age nor prevalence of chronic diseases was significantly different between frail and nonfrail; however, there were gender differences in that 67% of the frail and 90% of the nonfrail were female (Table 2).
Descriptive Data of the Variables
The means and standard errors of the means of the items comprising the "WHOAFC are presented in Table 3. Of the items comprising the WHOAFC, the items dealing with dressing and undressing and feeding oneself were scored as "performs without difficulty" by all subjects in both groups. Differences between the frail and nonfrail groups were not significant for six items (Nos. 2, 6, 7, 8, 9, and 10); the remaining 8 items were significantly different.
An examination of stability scores across the 6 measurement conditions for both the frail and nonfrail subjects demonstrated that stability declined in both the frail and nonfrail groups when the support surface and visual surround moved either individually or in combination (Table 4). Under Conditions 1 through 3, the stability scores are high (87.6% to 94.0%) even if the blue material visual surround moved, providing functionally inaccurate information to vision. However, as the support surface moved individually or in combination with visual inputs being absent because the eyes were closed or conflicting through movement of the visual surround, stability deteriorated in both groups from 65.4% to 35.2%, a 46% decline in the nonfrail group and 53.9% to 26.4%, a 51% decline in the frail group. The frail group had consistently lower stability scores across the last three measurement conditions. An inspection of the mean peak strength scores also demonstrated that for each movement strength was lower for the frail than the nonfrail group.
Prior to conducting the analysis, the pooled within-groups correlation matrix was examined for high correlations among the predictor variables. Correlations among the stability scores ranged from .22 to .62 and among the strength measures from .19 to .56; stability scores and strength measures correlated from .05 to .29. Correlations among the stability scores, strength measures, and age also demonstrated weak patterns of correlations (.03 to .34). These findings support the independence among the variables and the validity of entering each variable into the discriminant analysis.
When the predictor variables were entered into a discriminant analysis, stability score 4 (measurement with eyes open but moving surface) entered the model first (lambda .95, ? = .04), followed by dorsiflexion strength (lambda .93, p = .05), and then stability score 5 (eyes closed with moving surface) (lambda .90, ? = .04). The next step in the analysis removed stability score 4 from the equation (lambda .91, ? = .02). Therefore, the predictors discriminating between frail and nonfrail older adults were percent of sway with eyes closed with a moving surface and dorsiflexion.
DESCRIPTION OF STABILITY AND STRENGTH SCORES BY GROUP
To evaluate the sensitivity and specificity of the discriminant function, a classification analysis was conducted. As noted in Table 5, 54 or 64.4% of the grouped cases were correctly classified. The sensitivity and specificity of the model were similar in that 66.7% (n = 10) of the frail and 63.9% (n = 44) of nonfrail were correctly classified.
Findings from the correlation matrix suggest that age was related to neither balance nor strength in this sample. In addition, measures of balance and strength were independent. These findings are surprising because loss of muscle strength and balance are usually associated with age, and strength is associated with balance (Fiatarone & Evans, 1993; Whipple et al., 1987; Woollacott, 1993). It is possible that the weak correlations between strength and balance were because:
* An isometric measure of strength was used rather than an isokinetic measure or a measure of postural muscle response synergies.
* Other studies used one-legged timed balance measure to assess balance and that measure may confound measure of balance with strength.
* The independently living community-residing older adults in this sample were different in activity levels than subjects used in previous research (Lord, Caplan, & Ward, 1993; Speechley & Tinetti, 1991). As strength declines and the individual becomes more dependent, such as may be true of residents of nursing homes, strength and balance may become more intertwined.
The most parsimonious model distinguishing between frail and nonfrail people includes one balance and one strength measure. The one balance measure suggests that frail older adults have difficulty maintaining balance when vision is absent and the somatosensory system is provided with conflicting information, e.g., walking over soft carpet in the dark to get to the bathroom. With vision absent (eyes closed) and the somatosensory system given inaccurate information through sway-reference movement of the floor, the vestibular system is the remaining system being provided with accurate information. This finding is consistent with those of other investigators (Lord et al., 1993; Manchester, Woollacott, Zederbauer-Hylton, & Marin, 1989) who demonstrated that alterations in or deprivations of visual information are important contributors to decreased functioning and perceptions of health. Frail people may have difficulty selecting functionally useful information, in this study from the vestibular system, and have difficulty disregarding inaccurate information, such as that received by the somatosensory system because of the moving floor surface (Whipple, Wolfson, Derby, Singh, & Tobin, 1993; Woollacott, 1993). It is possible that the ability to coordinate leg and trunk muscles to maintain balance is diminished in frail older adults. Consequendy, frail people need assistance in their performance of those ADLs requiring muscle coordination to maintain balance. Frail people may also avoid those activities such as using stairs or doing housework, and in turn, perceive themselves as less healthy. This explanation is consistent with others (Gregg et al., 1996) who suggest physical function constitutes an important contributor to perceived health.
Another explanation for the association between balance and frailty is that although somatosensory inputs contribute as much as 58% of the sensory inputs for balance in the general population, somatosensory losses in the ankle have been estimated to affect more than 30% to 58% of older adults without neurological disease (Horak, Shupert, & Mirka, 1989; Lord, Russell, & Webster, 1991). This means that one third to one half of older adults may lack necessary input from the joint and tactile receptors in the ankles and feet for maintaining balance. It is possible that in this sample somatosensory losses contributed to diminished inputs for balance especially when the floor moved, and therefore, frail subjects could not maintain their balance with their eyes closed as well as the nonfrail.
The finding that frailty was also associated with poor dorsiflexion suggests that functional problems are experienced when one has difficulty elevating the front part of the foot during the swing phase of gait and controlling the angle of the foot at heel strike. These behaviors would be required to perform certain daily activities, such as walking on uneven surfaces, climbing stairs, and doing housework or yard work. This finding is consistent with that of Whipple et al. (1987) who found that ankle strength, especially dorsiflexion, was related to falls in elderly nursing home residents. Further, dorsiflexion strength is related to slower postural muscle response latencies among older adults (Woollacott, 1993; Woollacott et al., 1986). Slower postural muscle response latencies may be related to problems with carrying out complex daily tasks and falling.
The finding that age was not a significant predictor is unexpected because frailty is associated with aging (Brown et al., 1995). However, in this study, dorsiflexion and balance are better predictors of frailty than age. Age-related changes in sensory systems contributing to balance and declines in muscle strength in older adults are well documented (Woollacott, 1993).
CLASSIFICATION OF GROUPS BY PREDICTOR VARIABLES
It is possible that the characteristics of the sample influenced the findings of this study. The sample were all volunteers for an exercise project who were living independently in the community and not experiencing acute episodes of chronic illnesses. The independently living older frail people in this sample could be considered the "elite" frail, in that their personal and social resources were sufficient to allow them to remain independent (Rockwood et al., 1994). It is also possible that the combined measure of frailty used in this study did not fully capture the dimensions of frailty. While age and number of chronic illnesses were comparable across the two groups, other factors such as depression, nutrition, endurance, and polypharmacy were not measured (Speechley & Tinnetti, 1991; Winograd et al., 1991). Although no subjects had a history or clinical symptoms of vestibular disease, the clinical screening performed in the history and physical examination may not have detected vestibular pathology, when in fact it was present in a subclinical state. Finally, frailty may not be measurable at one point in time, as in this study, but must be measured over time, as proposed by Brown et al. (1995).
Balance and decreased strength have been found in previous research to be important characteristics differentiating frail from nonfrail people (Speechley & Tinnetti, 1991). This study clarifies the dimensions of these predictor variables, specifically that reliance on vision to control balance when the support surface is compliant combined with weak dorsiflexion strength are defining attributes of frailty.
Because none of the subjects had known neurological or vestibular pathology, it is possible that deconditioning of balance and strength systems explains the findings that balance and strength differentiate frail from nonfrail older adults. Nagi (1969) proposed that declines in functioning and health may be the result of primary (pathology-related) or secondary (disuse-related) alterations. Deconditioning may contribute to frailty independently or in combination with pathology.
To develop a more precise understanding of frailty and predictors of the condition, further work is warranted to refine the conceptual and operational definitions of the term. As Bortz (1993) points out, frailty lacks a clear conceptual framework. Instrument development research is needed to better capture the dimensions of the concept, and identify antecedents and consequences. Future research should consider adding additional predictor variables to the model. Other balance measurements that might be considered include the use of appropriate corrective strategies to maintain balance, e.g., ankle strategies, hip strategies, or stepping strategies, and efficiency of movement when people perform a movement that taxes or exceeds their limits of stability. Additionally, perceived endurance to carry out ADLs and independent ADLs (IADLs) may also be a plausible predictor variable. One meaning of frailty is that people perceive themselves as lacking energy, whether or not there are outward appearances to that effect (Brown et al., 1995).
Lastly, because impairments in dimensions of balance and in dorsiflexion differentiate frail from nonfrail people, specific exercise interventions designed to target these and improve the conditioning of the balance and strength systems could be considered. Exercises may prevent or treat frailty by improving the person's ability to carry out basic and IADLs and, in turn, contribute to a perception of good health.
When performing clinical assessments of older adults, not only should changes in disease status be evaluated, but also changes in functioning, perceived health, and impairments in balance associated with visual input and ankle strength should be considered. For example, ask older adults to stand with their eyes closed, preferably on piece of foam, to observe balance. Evaluate dorsiflexion strength while pushing the top of their feet against your hand. A comprehensive assessment is more likely to predict frailty, the ability to remain independent, and the need for services better than any one medical or clinical indicator. Nurses could add these clinical assessments of balance and ankle strength to develop a more comprehensive evaluation of frailty. Questions to evaluate the use of visual information when the somatosensory system is provided with conflicting vision could include: "Are you steady (balanced) if you walk on uneven ground out-of-doors or on very soft plush carpets?" If the answer to this question is no, referral to a physical therapist is warranted for further assessment and for balance and strength exercises. Balance and strength exercises that can be performed in the home are also available through lay publications such as How to Prevent Falls: A Comprehensive Guide to Better Balance (Perkins-Carpenter, 1991) and Pep Up Your Life (American Association of Retired Persons, n.d.). The findings of this study also lend empirical support to the time-honored nursing interventions to prevent falls and enhance function by using night lights and maintaining walking paths clear of obstacles.
- American Association of Retired Persons. (n.d.). Pep up your life. Washington, DC: Author.
- American College of Sports Medicine. (1995). Guidelines for exercise testing and prescription (5th ed.). Malvern, PA: Lea & Febiger.
- Bortz, W.M., Jr. (1993). The physics of frailty. Journal of the American Geriatrics Society, 41, 1004-1008.
- Bowsher, J., Bramlett, M., Burnside, I.M., & Gueldner, S.H. (1993). Methodological consideration in the study of frail elderly people. Journal of Advanced Nursing, 18, 873879.
- Brown, L, Renwick, R., & Raphael, D. (1995). Frailty: Constructing a common meaning, definition, and conceptual framework. International Journal of Rehabilitation Research, 18, 93-102.
- Büchner, D.M., & Wagner, E.H. (1992). Preventing frail health. Clinical Geriatric Mediane, 8, 1-17.
- Dayhoff, N., Topp, R., & Mikeskey, A. (1995). [Intertrial and test-retest reliability of measures of postural control using the Smart Balance Master]. Unpublished raw data.
- Ferrucci, L., Guralnik, J.M., Baroni, ?., Tesi, G., Antonini, E., & Marchionni, N. (1991). Value of combined assessment of physical health and functional status in community-dwelling aged: A prospective study in Florence, Italy. Journal of Gerontology, 46, M52-M56.
- Fiatarone, M.A., & Evans, W.J. (1993). The etiology and reversibility of muscle dysfunction in the aged [Special issue]. The Journals of Gerontology, 48, 77-83.
- Gregg, E. W, Kriska, A.M., Fox, K.M., & Cauley, J. A. (1996). Self-rated health and the spectrum of physical activity and physical function in older women. Journal of Aging and Physical Activity, 4, 349-361.
- Guralnik, J.M., & Simonsick, E.M. (1993). Physical disability in older Americans. Journal of the American Geriatrics Society, 48, 3-10.
- Hadley, E.C., Ory, M.G., Suzman, R., & Weindruch, R. (1993). Forward. Journal of the American Geriatrics Society, 48, vii-viii.
- Hoggan Health Industries. (1991). FETSystems: Manual muscle testing positions. Draper, UT: Author.
- Horak, RB., Shupert, CL., & Mirka, A. (1989). Components of postural dyscontrol in the elderly: A review. Neurobiology of Aging, 10, 727-738.
- Hodes, RJ. (1994). Frailty and disability: Can growth hormone or other trophic agents make a difference? Journal of the American Geriatrics Society, 42, 1208-1211.
- Huberty, C.J., & Barton, R.M. (1989). An introduction to discriminant analysis. Measurement and Evaluation in Counseling and Development, 22, 158-168.
- Lord, S.R., Caplan, G.A., & Ward, J.A. (1993). Balance, reaction time, and muscle strength in exercising and nonexercising older women: A pilot study. Archives of Physical Medicine and Rehabilitation, 74(8), 837-839.
- Lord, S.R., Russell, D., & Webster, LW. (1991). Postural stability and associated physiological factors in a population of aged persons. Journal of Gerontological Medical Science, 46, M69-M76.
- Manchester, D., Woollacott, M., Zederbauer-Hylton, N., & Marin, O. (1989). Visual, vestibular, and somatosensory contributions to balance control in older adults. Journal of Gerontology, 44, M118-M127.
- Nagi, S. (1969). Disability and rehabilitation. Columbus, OH: The Ohio State University Press.
- Nashner, L.M. (1982). Adaptation of human movement to altered environments. Trends in NeuroSciences, 5, 358-361.
- Nashner, L.M. (1990). Sensory, neuromuscular, and biomechanical contributions to human balance. In P. Duncan (Ed.), Balance: Proceedings of the APTA Forum (pp. 5-12). Alexandria, VA: American Physical Therapy Association.
- Nashner, L.M. (1994). Evaluation of postural stability, movements and control. In S.M. Hasson (Ed.), Clinical exercise physiology (pp. 199-234). St. Louis: Mosby.
- NeuroCom International, Inc. (1993). Smart BaUnce Master operator's manual: Version 3.1. Clackamas, OR: NeuroCom International, Inc.
- Pendergast, D.R., Fisher, N.M., & Calkins, E. (1993). Cardiovascular, neuromuscular, and metabolic alterations with age leading to frailty [Special issue]. The Journals of Gerontology, 48, 61-67.
- Perkins-Carpenter, B. (1991). How to prevent falls. Rochester, NY: Senior Fitness Productions, Inc.
- Rockwood, K., Fox, R.A., Stolee, P., Robertson, D., & Beattie, B.L. (1994). Frailty in elderly people: An evolving concept. Canadian Medical Association Journal, ISO[A), 489-494.
- Schulz, R, & Williamson, G.M. (1993). Psychosocial and behavioral dimensions of physical frailty [Special issue]. The Joumah of Gerontology, 48, 39-43.
- Speechley, M., & Tinetti, M. (1991). Falls and injuries in frail and vigorous community elderly persons. Journal of the American Geriatrics Society, 39, 46-52.
- Tabachnick, B.G., & Fidell, L.S. (1989). Using multivariate statistics (2nd ed.). New York: Harper Collins.
- Tinetti, M., Speechley, M., & Ginter, S.F. (1988). Risk factors for falls among elderly persons living in the community. New England Journal of Medicine, 319, 1701-1707.
- Topp, R., & Mikeskey, A. (1994). Reliability of isometric and isokinetic evaluations of ankle dorsi/plantar strength among older adults. Isokinetics and Exercise Science, 4, 157-163.
- Torres-Gil, F. (1990). Bill advances independence for older Americans. Aging Connection, 11, 1.
- Whipple, R.H., Wolfson, L.I., & Amerraan, P.M. (1987). The relationship of knee and ankle weakness to falls in nursing home residents: An isokinetic study. Journal of the American Geriatrics Society, 35, 13-20.
- Whipple, R., Wolfson, L., Derby, C, Singh, D., & Tobin, J. (1993). Altered sensory function and balance in older persons [Special issue]. The Journals of Gerontology, 48, 71-76.
- Wigglesworth, J., Dayhoff, N., Suhrheinrich, J. (1994). [The reliability of four measures of postural control using the Smart Balance Master]. Unpublished raw data.
- Winograd, C.H., Gerety, M.B., Chung, M., Goldstein, M.K., Donimguez, R, & Vallone, R. (1991). Screening for frailty: Criteria and predictors of outcomes. Journal of the American Geriatrics Society, 39, 778784.
- Woollacott, M.H. (1993). Age-related changes in posture and movement. Journal of the American Geriatrics Society, 48, 56-60.
- Woollacott, M.H., Shumway-Cook, A., & Nashner, L.M. (1986). Aging and posture control: Changes in sensory organization and muscular coordination. International Journal of Aging and Human Development, 23, 97114.
DESCRIPTION OF SMART BALANCE MASTER' MEASUREMENT CONDITIONS
CHARACTERISTICS OF SAMPLE BY GROUP
MEANS AND DIFFERENCES OF WORLD HEALTH ORGANIZATION ASSESSMENT OF FUNCTIONAL CAPACITY ITEMS BY GROUP
DESCRIPTION OF STABILITY AND STRENGTH SCORES BY GROUP
CLASSIFICATION OF GROUPS BY PREDICTOR VARIABLES