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The Journals of Gerontology Series A: Biological Sciences and Medical Sciences 55:M441-M445 (2000)
© 2000 The Gerontological Society of America

Spinal Flexibility and Balance Control Among Community-Dwelling Adults With and Without Parkinson's Disease

Margaret Schenkmana, Miriam Moreyb,d and Maggie Kuchibhatlab,c

a Physical Therapy Program, University of Colorado Health Sciences Center, Denver
b Claude D. Pepper Center, Center on Aging,
c Division of Biometry, Department of Family Medicine, Duke University Medical Center, Durham, North Carolina
d Veterans Administration Medical Center, Durham, North Carolina

Margaret Schenkman, Physical Therapy Program, University of Colorado Health Sciences Center, 4200 East Ninth Avenue, C-244, Denver, CO 80262-0244 E-mail: margaret.schenkman{at}UCHSC.edu.

William B. Ershler, MD


   Abstract
Top
 Abstract
Methods
 Results
 Discussion
 References
 
Background. One area of research that requires further elaboration is the relationship between impairments and functional limitations. By identifying specific contributors to functional limitations, it may be possible to establish intervention strategies, including exercise approaches, that can delay or ameliorate decline in function. The association between impaired spinal flexibility and functional limitations has not been studied in depth. The purposes of this study were to determine (a) the associations between spinal flexibility and functional limitations; (b) the relative contribution of spinal flexibility to specific functional limitations; and (c) how disease state (Parkinson's disease [PD] vs no PD) modified these relationships.

Methods. Participants included 251 community-dwelling adults, 56 of whom were with diagnosed PD and 195 were without PD or other specific disorders. Measures included spinal flexibility (i.e., functional axial rotation [FAR]) and configuration (i.e., thoracic kyphosis and lumbar lordosis), functional limitations (i.e., functional reach, supine-to-stand time, 10-m walk, and 360° turn).

Results. Canonical correlation (Can R) demonstrated significant associations between spinal measures and functional limitations (Can R = .488, p = .0001). After controlling for age, gender, race, body mass index, comorbidity, confidence, and depression, a multivariate regression model demonstrated that spinal flexibility contributed significantly to functional reach (R2 = .334 for the overall model, p = .0001). Based on the parameter estimate of 0.026, the results predict that FAR accounts for a 4.6-inch difference in reach distance between the least and most flexible of the participants. In addition, there were significant differences between almost all measurements for the PD compared with the non-PD participants.

Conclusion. Results clearly implicate spinal flexibility as a contributor to functional reach, a measure of functional limitation and an established measure of balance control. Further work is needed to determine the extent to which spinal flexibility can be improved and the effect of that improvement on balance.

DISABILITY is a substantial and growing problem for elderly persons. Functional limitations, as assessed by a patient's ability to perform activities of daily living, have been identified as significant predictors of nursing home use, hospitalization, and mortality (1)(2)(3). To delay or reverse losses of function, it is necessary to understand the steps that occur on the pathway to disability and to understand the multifactorial contributions to this process. Disablement models, including those of the World Health Organization (4) and Nagi (5), have been helpful in structuring thinking about relationships on the pathway to disability. For example, the Nagi model identifies relationships from pathology to impairment to functional limitation to disability. Specific pathological processes at the cellular level (e.g., Parkinson's disease) result in impairments in particular physiological systems (e.g., neurological, musculoskeletal, and cardiovascular). These impairments then contribute to functional limitations that affect the individual's performance of specific tasks (6). Disuse or abuse (e.g., sedentary lifestyle) can be the initiator of physiological decline within the disablement process (7). Appropriate interventions, including exercise, can then be developed to attenuate functional decline of elderly adults. Physical intervention can be specifically directed once the contributions have been identified of different physiological systems to function (8)(9)(10).

Much is known about the contributions of several impairments, including strength and cardiorespiratory fitness, to functional limitations. For example, at the Duke University Center on Aging, Morey and colleagues recently demonstrated that low cardiorespiratory fitness is a risk factor for functional limitations (9). Furthermore, the exercise parameters for improving the cardiovascular system are well established (11). Similarly, strength training can improve gait, even for people in the eighth decade of life (8). However, less is known about the contributions of flexibility to functional activities such as balance and walking. The few reports linking flexibility to function have focused on lower extremity flexibility (1)(12). Yet, spinal flexibility likely also contributes substantially to functional ability.

One of the earliest reports, from Bergström and colleagues (13), found moderately strong correlations between loss of spinal flexibility and difficulty in climbing stairs or using public transportation, as reported by a group of 79-year-old individuals. A subsequent study from our laboratory (14) demonstrated associations between spinal rotation and performance of a group of functional tasks (reaching, turning while standing, and supine to sitting). These results suggest that loss of spinal flexibility may be one source of functional limitation of elderly adults.

Investigators also have examined age relationships of spinal flexibility (e.g., cervical and lumbar), which demonstrated that older people generally are less flexible than younger people (15)(16)(17)(18)(19)(20)(21). Functional axial rotation (FAR) (14), a measure of combined spinal flexibility, illustrates the substantial differences that may occur among younger and elderly people. FAR incorporates all spinal segments as the seated individual turns to look over the right or left shoulder (14)(22). Total FAR, the excursion from the farthest available position looking over the right shoulder to the farthest available position looking over the left shoulder, was more than 300° for a sample of 20- to 40-year-old subjects but was under 220° (a difference of nearly 100°) for a sample of 76-year-old adults. Thus, even among community-dwelling adults without specific disorders, there is a wide range of available spinal flexibility as measured by FAR.

It is pertinent to better understand the contributions of spinal impairments to functional limitations. In addition, it is important to determine whether spinal contributions are independent of disease or are disease-specific. The purpose of this study was to further examine relationships between spinal flexibility (e.g., FAR) and functional limitations (e.g., functional reach) for a sample of community-dwelling adults with and without Parkinson's disease (PD). Specifically, we determined: (a) the overall associations between the impairment domain (i.e., spinal) and the functional limitation domain (i.e., functional reach, supine-to-stand, 10-m walk, and 360° turn); (b) the relative contribution of spinal flexibility to specific measures of functional limitation; and (c) how disease state (PD vs no PD) modifies these relationships.


   Methods
Top
 Abstract
 Methods
Results
 Discussion
 References
 
A sample of convenience was obtained for this study using baseline data from two clinical trials performed in the Claude D. Pepper Older Americans Independence Center at the Duke University Center on Aging. The protocols for the clinical trials were reviewed and approved annually by the Duke University and Veterans Administration institutional review boards. Detailed descriptions of the two intervention studies have been published elsewhere (23)(24).

Participants with PD (n = 56) were in stages II and III of Hoehn and Yahr (25) (community ambulators, possibly with some evidence of balance disturbance, but able to perform most daily activities independently). They had been on stable PD medications for at least 1 month, had not been hospitalized within the previous 3 months, and did not have other neurological conditions (e.g., stroke or multiple sclerosis). They had a Folstein Mini-Mental Status score (26) of at least 23. Community-dwelling adults without PD (n = 195) were included if they were over the age of 65, did not engage in regular vigorous exercise, and were free from contraindications to participate in an exercise clinical trial (i.e., unstable angina, uncontrolled hypertension, myocardial infarction within the previous 6 months, or congestive heart failure within the previous 12 months). They had a score of at least 7 on the Short Portable Mental Status Quotient (27).

Measures
All measures were obtained in the Claude D. Pepper Laboratory at Duke University Medical Center. The research assistants who obtained the measures underwent extensive training and inter- and intrarater reliability was determined (28)(29).

Characteristics of the sample.-- For all participants, age, gender, height, and weight were determined. Comorbidity was defined as total number of self-reported diagnoses. Depression was determined using the Center for Epidemiologic Studies–Depression scale (30), a 20-item Likert scale. Confidence in mobility was established using the Falls Efficacy scale (31), a 10-item Likert scale of self-reported confidence in performing ten common activities without falling.

Impairments.-- Spinal flexibility was quantified using FAR. This measure of combined spinal rotation tests the seated subject's ability to turn and look behind the body and incorporates all spinal segments (22). Motion during this test is not restricted to a single plane but is accomplished using whatever strategy the subject chooses. Total FAR (sum of right and left) is reported. Spinal configuration was quantified for thoracic kyphosis and lumbar lordosis. These measures were included for conducting canonical correlations that require more than one variable. Both thoracic kyphosis and lumbar lordosis were measured (32) in standing using the Debrunner's Kyphometer (Techmedica, Inc., Camarillo, CA).

Physical performance.-- Four physical performance tasks were quantified using previously reported protocols and constitute our assessment of functional limitations (24)(33). Functional reach distance, a clinical measure of balance control, was measured with the standing subject reaching as far forward as possible without taking a step (33). Time to move from supine to standing, a measure of transitional mobility, was measured at the subject's normal pace (24). Ten-meter walk time was included as a measure of gait (24). The number of steps to turn 360° to the right while standing, a higher level gait activity, was determined at the participant's own pace (24).

Data Analysis
We first compared community dwellers with and without PD, using the Student's t test, except for nonnormal data (Wilcoxon test) or categorical data (chi-square analysis). Next, we examined relationships between variables from the physical performance and impairment domains. We used canonical correlations to identify these relationships (34).

Finally, we used multiple regression analyses to determine the relative contributions of spinal flexibility (as determined by FAR) to each of the following functional limitation outcome variables: functional reach, 360° turn in standing, and supine to stand. Each regression model examined included a single predictor variable, spinal flexibility; a single outcome variable of functional limitation; and the following covariates: age, gender, race, comorbidity, body mass index, affect, confidence, and depression. (For the nonnormal dependent variables [supine to standing, 10-m walk, and 360° turn], we used log-transformed data.) Last, to determine if the effect of the predictor variable (FAR) on the outcome variable (functional reach) is determined by disease state (PD vs no PD), we examined the interaction model.


   Results
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 Methods
 Results
Discussion
 References
 
Characteristics of the two samples are shown in Table 1 . The two samples were comparable in terms of age and body mass index. The PD sample was composed predominantly of men, with few minorities, whereas the community dwellers without PD were predominantly composed of women, with nearly 25% minority representation.


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  		Table 1. Characteristics of the Sample ({chi}, SD unless noted) (comparisons via Student's t test unless noted)

 
Measures of spinal flexibility and functional limitations also are shown in Table 1 . Total FAR ranged from 110° to 285° (a total of 175° between the least and most flexible participants). On average, those participants with PD were significantly less flexible than were their counterparts without PD. Participants with PD also had significantly more impaired balance control, as estimated by functional reach. Similarly, participants with PD were significantly more impaired in 360° turn (seconds), 10-m walk (seconds), and supine to stand (seconds). There were no significant time differences to complete the 360° turn between the two subject groups.

Canonical correlations were used to examine the overall association between spinal flexibility/configuration and functional limitations. Results demonstrate a significant and substantial relationship (Can R = .488, p = .0001) (Table 2 ). Multiple regression analysis was used to determine the relative importance of spinal flexibility for individual measures of functional limitations. Results demonstrated a significant contribution of spinal flexibility (FAR) to functional reach. The overall model (p = .0001) accounted for 33.4% of the variance, with covariates accounting for 27.5% in functional reach (Table 3 ). Thus, 6.1% of the variance in reach distance was accounted for by spinal flexibility. Spinal flexibility also was a significant predictor of both supine-to-stand time and the number of steps in the 360° turn. However, the parameter estimates were not clinically meaningful for these two variables, and these data are not further described. The influence of disease state (with or without PD) on the model was analyzed; the interaction of group by spinal flexibility did not contribute significantly to this model.


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  		Table 2. Associations Behind Domains (canonical correlations)

 

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  		Table 3. Regression Analyses to Determine Relative Contribution of Spinal Flexibility to Functional Reach

 

   Discussion
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 Abstract
 Methods
 Results
 Discussion
References
 
The spine forms the structural base from which functional movement is generated. One could infer reasonably that spinal flexibility should have a profound influence on a person's ability to move and function. To date, however, there have been only a few investigations into relationships between the spine and functional limitations (13)(14)(35). Data from this study extend prior evidence that implicates spinal flexibility as an important contributor to a common functional activity. Specifically, this investigation demonstrated the relationship between spinal flexibility and functional reach, an established measure of balance control.

To better understand the specific contribution of spinal flexibility to balance control, we examined the data using regression analysis, demonstrating, for the first time, that the contribution of spinal flexibility to balance control is significant. We were unable to determine whether the 6.1% of variance, contributed by FAR, is clinically meaningful. However, the overall importance of spinal flexibility for balance control might be appreciated by interpreting the parameter estimate in context of the 175° range of values between the most and least flexible participants within this sample. Based on the parameter estimate of 0.026, we would predict that FAR accounts for a 4.6-inch difference in reach distance between the least and most flexible of the participants (175° x .026 inches). For functional reach, the range between the lowest and greatest reach was 16 inches. Theoretically, FAR could have accounted for more than one-quarter of the difference in lowest compared with greatest reach distance. For certain individuals, this could be a clinically significant contribution. Longitudinal studies should be performed to confirm this conjecture and to determine the characteristics for which limitations in FAR are clinically meaningful.

In this study, we investigated a sample of community-dwelling adults with and without PD to determine whether relationships between spinal flexibility and task performance transcend disease state. In a previous article (36), we suggested that spinal flexibility contributed to task performance of persons with relatively early PD, independent of the direct neurological effects of the disease (e.g., rigidity or bradykinesia). For optimal care, it is important to understand the extent to which spinal impairments (as well as impairments in other physiological systems) contribute to functional limitations in patients with neurological diseases such as PD. Physical intervention may be helpful in preserving or restoring functional ability, even when the primary effects of the disease exist (e.g., rigidity, bradykinesia, resulting from neurotransmitter imbalances of PD).

To examine this issue, we specifically chose a sample of patients in the early and middle stages of PD, when alterations of spinal configuration and flexibility might be expected but before frank postural instability has occurred. Our results clearly support our earlier suggestion indicating that the relationship between spinal flexibility and functional limitations is independent of PD. Consistent with the results of this investigation, a recent clinical trial from the Duke University Claude D. Pepper Center (24) demonstrated that persons in relatively early stages of Parkinson's disease, who participated in a program to improve spinal flexibility, showed significant improvements in FAR and functional reach compared with participants in a control group who did not exercise. A companion study (23) comparing spinal flexibility exercises plus aerobic conditioning with aerobic conditioning alone for community-dwelling adults without PD likewise showed significant improvements in spinal flexibility, although the changes were small. It is unclear whether intensity of exercise was adequate to produce clinically meaningful changes. Studies with a variety of subject groups are warranted to elucidate the importance of including exercise to increase spinal flexibility for elderly adults and for those with disorders that impair spinal flexibility.

The current study demonstrated statistically significant impairments of flexibility and physical performance in people with PD compared with community-dwelling adults without PD. Yet to be determined is the extent to which these differences in spinal flexibility reflect true structural differences between the two groups versus learned dysfunction. Similarly, it is yet to be determined whether PD participants improve FAR and functional reach of PD with exercise (24) because of true changes in structure or because of improved patterns of movement within the available structure. Finally, the question must be raised whether a 1-second difference between groups for time to turn or to walk 10 meters is clinically meaningful. In this regard, it is noteworthy that the PD participants were in the relatively early stages of PD. Future work should examine the rate of increase in time to complete functional tasks and should determine at what point the increased time is clinically meaningful.

Two methodological issues should be noted. First, data for several measures were nonnormal, although not highly skewed. For these variables, we used the Wilcoxon test for the bivariate group comparisons (Table 1 ). In the regression analysis (Table 3 ) examination of the relationship between FAR and functional reach, the only nonnormal variable was confidence in mobility. We did not transform this variable, because it was included only as a control variable in the model.

Second, the PD group of participants was composed of a disproportionate number of men, whereas the non-PD group was composed of a disproportionate number of women. Gender differences between the two groups might have accounted for some of the group differences (Table 1 ) observed in this study. In multivariate regression, gender contributed significantly to the variance in functional reach (Table 3 ). However, it is noteworthy that we controlled for gender in the regression model; even so, spinal flexibility (FAR) made a significant contribution to balance control (functional reach).

In summary, results of the current study demonstrate the importance of spinal flexibility in maintaining balance control in later life. Spinal flexibility joins muscle strength and cardiorespiratory fitness as a physiological contributor to functional limitations that are amenable to physical intervention. The circumstances in which spinal flexibility can be improved with exercise warrant further investigation, as does the extent to which improvements in flexibility are related to improved task performance and to overall functional ability. Studies should be performed to determine the following and related questions: Can flexibility be retained by appropriate exercise for healthy adults as they age? Does improved flexibility decrease balance dysfunction for those with and without specific diseases? What are the best treatment strategies, combining flexibility, aerobic conditioning, and strength training, for optimizing physical ability and overall function of specific subject groups? Studies also should be performed to determine whether improvements of spinal flexibility can lessen physical disability of those at risk for loss of independence.


   Acknowledgments
 
The authors gratefully acknowledge members of the measurement team from the Duke University Claude D. Pepper Center who performed all measurements and the participants who gave graciously of their time. This study was supported by the National Institutes of Health, National Institute on Aging, Claude D. Pepper Older Americans Independence Center (Grant 5 P60 11268) and the National Institutes of Health, National Center for Research Resources, General Clinical Research Centers program (Grant MO1-RR-30).

Received April 26, 1999

Accepted December 18, 1999


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 Discussion
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