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The Journals of Gerontology Series A: Biological Sciences and Medical Sciences 60:1310-1314 (2005)
© 2005 The Gerontological Society of America

Trunk Repositioning Errors Are Increased in Balance-Impaired Older Adults

Allon Goldberg1,3,, Manuel Enrique Hernandez2 and Neil B. Alexander1,3,4

1 Institute of Gerontology, 2 Department of Biomedical Engineering, and 3 Mobility Research Center, Division of Geriatric Medicine, Department of Internal Medicine, The University of Michigan, Ann Arbor.
4 VA Ann Arbor Health Care System Geriatric Research, Education and Clinical Center, Michigan.

Address correspondence to Allon Goldberg, PT, PhD, Department of Health Care Sciences, Program in Physical Therapy, Wayne State University, 259 Mack Ave., Detroit, MI 48201. E-mail: agoldberg{at}wayne.edu


   Abstract
Top
 Abstract
Methods
 Results
 Discussion
 References
 
Background. Controlling the flexing trunk is critical in recovering from a loss of balance and avoiding a fall. To investigate the relationship between trunk control and balance in older adults, we measured trunk repositioning accuracy in young and balance-impaired and unimpaired older adults.

Methods. Young adults (N = 8, mean age 24.3 years) and two groups of community-dwelling older adults defined by unipedal stance time (UST)—a balance-unimpaired group (UST > 30 seconds, N = 7, mean age 73.9 years) and a balance-impaired group (UST < 5 seconds, N = 8, mean age 79.6 years)—were tested in standing trunk control ability by reproducing a ~30° trunk flexion angle under three visual-surface conditions: eyes opened and closed on the floor, and eyes opened on foam. Errors in reproducing the angle were defined as trunk repositioning errors (TREs). Clinical measures related to balance, trunk extensor strength, and self-reported disability were obtained.

Results. TREs were significantly greater in the balance-impaired group than in the other groups, even when controlling for trunk extensor strength and body mass. In older adults, there were significant correlations between TREs and three clinical measures of balance and fall risk, UST and maximum step length (–0.65 to –0.75), and Timed Up & Go score (0.55), and between TREs and age (0.63–0.76). In each group TREs were similar under the three visual-surface conditions. Test–retest reliability for TREs was good to excellent (intraclass correlation coefficients ≥0.74).

Conclusions. Older balance-impaired adults have larger TREs, and thus poorer trunk control, than do balance-unimpaired older individuals. TREs are reliable and valid measures of underlying balance impairment in older adults, and may eventually prove to be useful in predicting the ability to recover from losses of balance and to avoid falls.

FALLS are a major cause of morbidity and mortality in older adults, with numerous factors predisposing the older adult to a fall. Strategies involving activation of the upper and lower extremities as well as trunk musculature, have been identified as critical in postural control (1–4), serving either to maintain the body's center of mass within the base of support (BoS), or to return it rapidly to within the BoS, thereby maintaining postural equilibrium. As the trunk contributes more than any other body segment to total body weight [reviewed in (5)], the changing position of the body's center of mass relative to the BoS is markedly influenced by changes in trunk positioning, such as during performance of activities of daily living. Even more important is the role of trunk control in recovery from losses of balance; controlling trunk flexion motion is a key contributor to recovery from a stumble (3). Many losses of balance occur in an anterior direction as a result of a trip, and thus usually require trunk control as the trunk rotates anteriorly.

One domain of trunk control, trunk position sense, is the ability to accurately position the trunk at predetermined points in the range of motion in the sagittal plane (6–8). Trunk repositioning protocols require participants to accurately reposition and control the flexing trunk and could therefore be a useful measure of trunk control. However, trunk repositioning accuracy studies to date have largely addressed trunk position sense in patients with low back pain and have not explored the role of trunk position sense in relation to postural control and fall avoidance in older adults. Given the importance of the trunk in postural control in older adults, we rationalized that the ability to control trunk position (trunk repositioning accuracy) can serve as a measure of postural control and would thus be more impaired in those persons with clinically apparent problems with standing balance. Furthermore, postural instability, often measured in terms of trunk motion, is increased under conditions of reduced visual and somatosensory input. Under reduced sensory input conditions, for example, trunk sway is increased in those persons with vestibular loss (9), and sway velocity is increased with age (10). We therefore theorized that trunk position sense would be impaired in older versus young adults, and in balance-impaired versus unimpaired older adults, particularly under conditions of reduced sensory inputs.

To our knowledge, no studies have investigated the relationship between trunk position sense ability and balance impairment in older adults. We therefore sought to assess trunk position sense difficulty, defined as trunk repositioning errors (TREs, measured in degrees), in balance-impaired (BI) and unimpaired (O) older adults. Our objectives were to compare TREs between three adult groups (BI, O, and Y [young controls]) and to relate trunk repositioning performance measured under differing visual-surface conditions to standard clinical balance measures. We hypothesized that TREs would increase with age (O larger than Y) and in the presence of a balance impairment (BI larger than O), particularly under conditions of limited visual and foot sensory input (vision occluded and standing on foam). Measurement of TREs may eventually prove to be useful in quantification of balance impairment, as a key component of trunk control in recovery from losses of balance, and as a predictor for future falls.


   METHODS
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 Methods
Results
 Discussion
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Participants/Groups
Young healthy volunteers aged 18–30 years, screened for musculoskeletal or neurological abnormalities, were students at the University of Michigan. Community-dwelling, functionally independent volunteers aged 65 years or older were recruited largely from a database maintained by the University of Michigan Older Americans Independence Center Human Subjects Core. Older participants underwent a screening medical history and physical examination by a nurse practitioner, and were excluded from the study if they were medically unstable (e.g., chest pain upon exertion, dyspnea, infection), reported frequent back or lower extremity pain, or had a history of neurological disease that might affect balance (e.g., cerebral vascular accident [CVA], Parkinson's disease). At screening, self-reported difficulty in mobility-related daily activities was assessed using The Established Populations for Epidemiologic Studies of the Elderly (EPESE) battery (11). During screening, older participants were classified as balance-unimpaired if they had a unipedal stance time (UST) of >30 seconds, and as balance-impaired if UST was <5 seconds. Deficits in UST, defined as the ability to stand on one leg unsupported for 5 seconds, are significant predictors of injurious falls (12). The O group reflected a "healthy" cohort, with pathologies being limited to asymptomatic knee osteoarthritis (in two individuals) and hypertension (in one individual). The BI group had more abnormalities on history and examination than did the O group, with gait asymmetries (2/8 individuals) and lower extremity musculoskeletal conditions (7/8 individuals). None of these conditions were symptomatic at the time of assessment, and all participants completed the protocol.

Trunk Repositioning Errors
Testing took place while standing under three visual-surface conditions: eyes opened (EO FLOOR), eyes closed (EC FLOOR), and on foam of density 44.85 kg/m3 (2.8 lb/ft3) (EO FOAM). To assess TREs, a digital inclinometer (PRO-360; Irvan-Smith, Concord, NC) with precision to 0.1° was held at the level of the T4 spinous process. Participants flexed the trunk approximately 30° in the sagittal plane, holding the position for a count of 3 seconds (position 1). After returning to the upright position, participants attempted to duplicate the previously attained angle. Participants indicated verbally when they felt they had reached the angle, and held their position for a count of 3 seconds (position 2). The absolute difference in degrees between positions 1 and 2 was defined as the TRE. Participants generated five scores for each visual-surface condition. For each condition, the highest and lowest scores were discarded, and the mean of the remaining three scores represented the TRE score.

Clinical Balance Measures
UST.-- With arms folded across the chest, participants stood on their dominant leg and lifted the foot of the other leg approximately 2 inches from the medial malleolus of the stance leg. A practice trial preceded two experimental trials. The better time (maximum 30 seconds) was recorded as UST.

Maximum Step Length.-- Maximum step length (MSL) is a measure of stepping ability that correlates with standard balance and functional mobility measures and a history of falls (13,14). The MSL is the maximum distance that participants can step forward with their dominant leg and still successfully return to the original position. Following a practice trial and with participants' arms folded across the chest, MSL was recorded as the mean of five trials of maximum step distance.

Functional Reach.-- Functional reach (FR) is a reliable measure of balance and margin of stability (15), and as it requires participants to reach forward while flexing the trunk, it is a dynamic measure of postural control. FR is defined as the maximal distance one can reach forward beyond arm's length while maintaining a fixed BoS in standing, and is measured with a yardstick affixed to the wall at the level of the acromion (15). A practice trial preceded three experimental trials, and FR was recorded as the mean distance over three trials.

Timed Up & Go.-- Timed Up & Go (TUG) is a reliable test for quantifying functional mobility, including dynamic balance, in older adults (16). Participants sat in a chair, stood up, and walked 3 meters at a "comfortable and safe pace" before turning around and returning to the seated position. A practice trial preceded three experimental trials, and TUG score was recorded as the mean time over three trials.

Trunk Extensor Strength
Trunk extensor isometric strength was evaluated using a Biodex Back Attachment affixed to a Multi-Joint System 2 AP dynamometer (Biodex Medical Systems, Shirley, New York). Participants were supported in the seated position via chest, pelvic, and thigh straps, with the arms folded and the trunk and lower extremities configured at approximately 90° to each other. After a practice trial, participants exerted a maximal trunk extension contraction for 3 seconds against a pad located at the interscapular region. Participants completed two trials, with a ~45-second rest in between trials. The higher score was recorded as the peak torque. If the two torque measurements were more than 15% different from each other, an additional trial was performed to achieve consistency.

Statistical Analysis
Group comparisons for age, height, weight, UST, MSL, FR, TUG, and trunk strength were evaluated using one-way analysis of variance (ANOVA). Group comparisons for TREs were evaluated using analysis of covariance (ANCOVA) with repeated measures for TREs measured under three visual-surface conditions. Body mass and trunk strength were included in the model as covariates. Univariate ANCOVAs, again covarying body mass and trunk strength, were conducted for TREs measured under each of the three visual-surface conditions when there were significant group differences. Post hoc tests with Bonferroni corrections for multiple comparisons between groups were conducted. Differences in EPESE score between the older groups were evaluated using an independent samples t test. Repeated-measures ANOVA was used to determine whether TREs differed between the three visual-surface conditions within each group. Intertrial reliability using one rater for the three TRE measures was assessed using the intraclass correlation coefficient (ICC) (17). Correlations between TREs and age, clinical balance measures, and trunk strength were evaluated using the Pearson correlation coefficient.


   RESULTS
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 Methods
 Results
Discussion
 References
 
Participant Characteristics and Clinical Measures
Characteristics of the 23 participants included in the study are presented in Table 1. Mean age and weight tended to be higher in the BI group than in the O group, but the differences were not statistically significant. By definition, there were significant differences in UST of the BI group compared to those in the other groups (p <.05), indicating balance capabilities in the Y and O groups superior to those in the BI group (Table 2). Similarly, there were significant differences in TUG of the BI group compared to that in the other groups (p <.05), indicating reduced functional mobility and dynamic balance capabilities in the BI group. There were significant differences in MSL and FR between the Y and older groups (p <.05). There were no significant differences in the MSL and FR measures between the older groups (Table 2), although MSL normalized for body height was significantly different between the older groups (O, 0.51 vs BI, 0.40; p <.05). Trunk strength tended to be greater in the O versus BI group and in the Y versus O group, although not at significant levels (Table 2), with similar results achieved after normalizing for (dividing by the product of) body height and weight. EPESE scores differed significantly between the older groups (O, 0.4 vs BI, 2.8; p <.05, Table 2), indicating increased difficulty with mobility-related daily activities in BI individuals.


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  		Table 1. Characteristics of Young (Y), Balance-Unimpaired Older (O), and Balance-Impaired Older (BI) Adults.

 

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  		Table 2. Clinical Measures in Young (Y), Balance-Unimpaired Older (O), and Balance-Impaired Older (BI) Adults.

 
Trunk Repositioning Errors
In the repeated-measures model of analysis of group differences, even when covarying body mass and trunk strength, TREs were significantly different between the three groups (p <.01). Univariate tests and post hoc group comparisons demonstrated that, for each of the visual-surface conditions, TREs were significantly larger (ranging from 1.9- to 3.0-fold) in the BI group than in the other groups (p <.01) (Figure 1). Mean TREs (± standard error of the mean [SEM]) ranged from 2.34 ± 0.34 to 2.82 ± 0.37 in the Y group, from 3.36 ± 0.62 to 3.86 ± 0.70 in the O group, and from 7.10 ± 0.68 to 7.50 ± 0.73 in the BI group (Figure 1). In contrast to the main effect for groups, there were no significant main effects observed for the covariates (trunk strength and body mass) in either the repeated-measures or univariate ANCOVAs (p >.05). Correlations between trunk strength and TREs ranged from –0.32 to –0.37 (p >.05) for the whole sample, and from –0.10 to –0.30 (p >.05) for the older participants. There was a trend toward greater TREs in the O than in the Y group (p >.05; Figure 1). Significant correlations between TREs and age for the older groups combined (Pearson's r = 0.63–0.76, p <.05) suggest that increases in TREs are associated with aging in the older adult groups. Within each group, TREs were similar under each visual-surface condition (Figure 1), indicating that neither reduction of vision nor foot sensory input had an effect on trunk repositioning accuracy.



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  		Figure 1. Mean (± standard error of the mean [SEM]) trunk repositioning errors (TREs) (degrees) for three groups measured under three visual-surface conditions. TREs are significantly larger in the balance-impaired group than in each of the other groups (p <.01). Within each group, there were no significant differences in TREs measured under the three visual-surface conditions. EO = eyes opened; EC = eyes closed

 
For the entire sample, TREs for each visual-surface condition correlated significantly with UST and MSL (r = –0.63 to –0.80, p <.01) and with TUG (r = 0.46–0.60, p <.05) (Table 3). FR did not correlate significantly with TREs. For older adults only, TREs for each visual-surface condition correlated significantly with UST and MSL (r = –0.65 to –0.75, p <.01) (Table 3), and EC FLOOR correlated significantly with TUG (r = 0.55, p <.05). These correlations suggest TREs to be valid measures of underlying balance impairment, specifically in older adults.


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  		Table 3. Correlations Between Trunk Repositioning Errors (TREs) and Clinical Balance Measures.

 
Same day single-rater intertrial test–retest reliability of the three TRE measures was good to excellent. ICC values for EO FLOOR, EC FLOOR, and EO FOAM were 0.79, 0.74, and 0.81, respectively (p <.01).


   DISCUSSION
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 Methods
 Results
 Discussion
References
 
We present the first data demonstrating that older balance-impaired individuals have larger (average twofold) TREs and thus poorer trunk control compared to balance-unimpaired older individuals. These are the first data linking commonly used measures of clinical balance with those of trunk position sense. The strongest correlations were between TREs and UST (a test of static balance and lower extremity muscle strength), and TREs and MSL (a test of dynamic balance and lower extremity muscle strength and joint range of motion), suggesting that accurate control of the trunk is dependent on leg function as well as balance.

For the 15 older participants, we found strong correlations between TREs and three clinical balance measures (UST, MSL, and TUG). We were unable to compare our measure of trunk control (TRE) in older adults with literature values, as this study is to our knowledge the first to measure TREs in older adults. For the younger participants, however, our measures of repositioning accuracy are similar to those reported in other studies (8,18). In addition, as ICCs for the three TREs range from 0.74 to 0.81, TREs exhibit good to excellent same day intertrial reliability. These results suggest that TREs are reliable and valid measures of underlying balance impairment. Studies involving lower extremity joints have generally demonstrated age-related declines in joint position sense (19,20), although a recent study demonstrated no differences in hip joint position sense between young and older participants (21). Likewise, the present study failed to demonstrate significant differences in mean TREs between the young and balance-unimpaired older group, although a trend toward higher TREs in the O group than in the Y group was observed. However, significant correlations between age and TREs in older adults suggest that increases in TREs are associated with aging.

In all three groups, TREs were similar under each visual-surface condition. Our results confirm those of others demonstrating that TREs are similar in the eyes open and closed situations (18). These results suggest that trunk repositioning accuracy may not be dependent on vision or lower extremity somatosensation. As postural control involves interactions among sensory orientation inputs from the visual, vestibular, and somatosensory systems (22,23), the uncoupling of trunk position sense from visual and lower extremity somatosensory inputs raises questions as to the role of the vestibular system in trunk control. Results from galvanic vestibular stimulation experiments suggest that the vestibular system may control postural orientation via trunk control (24), but the role, if any, of the vestibular system in trunk positioning accuracy is unknown. The importance of muscle spindles as mediators of joint position sense is well established, but their role in control of spinal positioning sense has only recently been investigated (25). A 5-second 70-Hz frequency manually applied vibratory stimulus over the multifidus muscles was associated with repositioning inaccuracies in the lumbosacral spine in seated young individuals, suggesting that accuracy in control of spinal positioning is subservient to precise muscle spindle inputs of the paraspinal muscles (25). Further support for local mediation of trunk position sense comes from studies showing that bracing of the lumbar region in participants with low back pain (26) and asymptomatic (27) participants improved trunk flexion positioning accuracy. These studies suggest that local somatosensory inputs are important in control of the trunk in the sagittal plane. It is thus possible that both local (muscle afferent somatosensory) and distant (vestibular) factors influence trunk positioning accuracy.

Large trunk flexion angles increase the torso moment arm (28) and the difficulty of the recovery task after a trip (29), suggesting that control of the flexed trunk is critical in avoiding a fall. In the present study, TREs were measured at ~30° of trunk flexion. This ~30° of flexion is particularly relevant given that laboratory studies have shown that maximum trunk flexion angles after induced trips and stumbles range from 18.3° to 33.8° (3,29). It is unclear whether there exists a threshold of maximum trunk flexion beyond which recovery after a trip is not possible.

Control of the trunk during activities of daily living likely requires contributions from trunk and lower extremity musculature, although the relative contributions of each remain to be determined. For example, forward bending from neutral standing is associated with increasing myographic activity of paraspinal trunk extensor musculature as flexion range of motion and the moment arm of the torso increases (28). This suggests that increased activation of trunk extensor musculature is important in trunk flexion control. However, laboratory investigations of trunk control after induced trips raise the possibility that trunk extensor muscle strength does not contribute to arresting trunk flexion in the early recovery phase from losses of balance. Instead, hip extensors (hamstrings and gluteus maximus) may have roles in trunk control as they directly influence pelvic orientation (29). In the present study, there were no significant correlations between trunk extensor strength and TREs. After controlling for variation in trunk strength, there were still significant differences in TREs between the groups, suggesting that the ability to accurately reposition the trunk is dependent on other factors besides trunk strength. Repositioning the trunk accurately involves a complex multisegmental test with synergistic motion at multiple joints concurrently during trunk flexion, including motions of the pelvis on the femoral head (hip joint flexion), and the distal tibia and fibula on the talus (ankle joint plantarflexion). This suggests that multiple components of the lower extremity neuromusculoskeletal system potentially influence trunk function and position sense. To this end, proximal and distal lower extremity deficits in strength, proprioception, coordination, range of motion, and flexibility, and their influences on trunk positioning sense and fall risk in older adults need to be elucidated. For example, future investigations should consider relationships between lower extremity muscle strength, particularly at the hip, and trunk control measures such as TREs. Although there was no difference in TREs under the various visual-surface conditions within each of the present study groups, TRE testing among clinically impaired populations who are likely to be dependent on visual and/or somatosensory function (such as those with vestibular deficits or peripheral neuropathy) may be useful for screening and assessment of disease severity. Development of protocols to reduce TREs in these and other clinical populations adds a trunk control focus to rehabilitation protocols that frequently focus on nonspecific "balance" and extremity strength training.

This is the first report highlighting that trunk control as measured by trunk repositioning accuracy is reduced in balance-impaired older adults, and that TREs are reliable and valid measures of underlying balance impairment in older adults. Given the importance of trunk control in maintenance of stance and in fall recovery, TREs may ultimately be proven to be a marker of fall risk, and interventions that reduce TREs may also then reduce falls.


   Acknowledgments
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 Results
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We acknowledge support of the National Institute on Aging (NIA) Grant AG08808 (University of Michigan Claude D. Pepper Older Americans Independence Center), NIA Grant AG10542, NIA Institutional Training Grant T32 AG00114 (Multidisciplinary Research Training in Aging), as well as the Office of Research and Development, Medical Service and Rehabilitation Research and the Development Service of the Department of Veterans Affairs. Dr. Alexander is a recipient of the K24 Mid-Career Investigator Award in Patient-Oriented Research (AG 109675) from the NIA. Dr. Goldberg is the recipient of the 2004 Fellowship for Geriatric Research Award from the Section on Geriatrics of the American Physical Therapy Association.

The assistance of Diane Scarpace, RN, NP; Ravinder Goswami; and Eric Pear in participant assessment and data collection is acknowledged.

Allon Goldberg is now with the Department of Health Care Sciences, Program in Physical Therapy, Wayne State University, Detroit, Michigan.


   Footnotes
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Decision Editor: John E. Morley, MB, BCh

Received August 24, 2004

Accepted October 28, 2004


   References
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