Age-Related Changes in Postural Control in

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Research Report Age-Related Changes in Postural Control in Physically Inactive Older Women Juliana Teles Tavares, PE, MSc1; Daniela Aparecida Biasotto-Gonzalez, PT, PhD1; Nárlon Cássio Boa Sorte Silva, PE, MSc2; Frank Shiguemitsu Suzuki, PE, PhD1; [AQ00] Paulo Roberto Garcia Lucareli, PT, PhD1; Fabiano Politti, PT, PhD1

ABSTRACT

Background and Purpose: The maintenance of postural control is influenced by the complexity of a given task. Tasks that require greater attention and cognitive involvement increase the risk of falls among older adults. The aim of the present study was to evaluate the adaptation of the postural control system to different levels of task complexity in physically inactive young and older women. Methods: A cross-sectional study was conducted with adult women classified as physically inactive based on the results of the International Physical Activity Questionnaire. The participants comprised 27 young (20-30 years of age) and 27 older (60-80 years of age) women. Sway velocity of the center of pressure in the anterior-posterior and medial-lateral directions was calculated using a force plate under 6 conditions: standing directly on the force plate or on a foam placed over the force plate, eyes open or closed, and task complexity with and without the foam. Results and Discussion: A 2-way analysis of variance revealed that sway velocity increased in both groups when the task conditions were altered. The older women exhibited significantly greater sway velocity compared with the young women on all tasks. However, the patterns of postural control adaptation to the different levels of complexity were similar among all participants. Conclusions: In this study, the adaption of the postural control system to different levels of task complexity did not differ between physically inactive young and physically inactive older women. However, the physically inactive older women exhibited greater sway velocity compared with the young women. Key Words: age-related, dual-task paradigm, older adult women, postural control

INTRODUCTION

DOI: 10.1519/JPT.0000000000000169

Postural control depends on the integration of information from the vestibular, visual, and somatosensory systems.1 This integration among systems can be impaired during the aging process, affecting the neuromuscular control required for maintenance of postural control.2 The consequence of these alterations is an increased risk of falls in the population of older adults, with as many as 1 fall per year among at least a third of this population.3 Falls represent up to 5 times more injury-related hospitalizations than any other cause,4 accounting for a significant increase in the cost of health care.5 Approximately 10% to 20% of older adults who have suffered a fall are hospitalized with serious injuries,6 and many of these individuals subsequently restrict their activities due to fear of further falls,7 resulting in inactivity, the loss of independence with regard to performing activities of daily living, and greater susceptibility to chronic diseases.7,8 The reasons for the loss of balance and increased susceptibility to falls among older adults are not fully understood. However, diminished physical and motor abilities may be the main factors.9 In addition to a decline in muscle strength resulting from a decrease in motor units and the atrophy of muscle fibers,10,11 reductions are found in reaction time and reflexes, especially in the ankles, along with changes in proprioception.9 The age-related changes that occur in the sensory and motor systems seem to increase the need for cognitive resources or attention during sensory-motor activities.12 Tasks that require greater cognitive or attention, such as dual tasks, are also affected by the aging process and increase the difficulty with regard to postural control.12,13 Studies addressing the effects of aging on the short-term adaptability (motor control adjustment) of compensatory postural responses to predictable perturbations (ie, constant frequency and amplitude) indicate that the central nervous system maintains the ability to modify balance behavior based on prior experience.14,15 In unpredictable situations, however, the central nervous system uses a previously established optimal movement strategy in addition to its dependence on reactive responses to decrease the likelihood of losing balance. Due to the age-related decline in functional aspects, older adults likely optimize their

Journal of GERIATRIC Physical Therapy

1

(J Geriatr Phys Ther 2017;00:1-6.) 1Postgraduate

Program in Rehabilitation Sciences, Physical Therapy Department, Universidade Nove de Julho, São Paulo, Brazil. 2Faculty of Health Sciences, School of Kinesiology, Western University, London, Ontario, Canada. [AQ02] The authors declare no conflicts of interest. Address correspondence to: Fabiano Politti, PT, PhD, Rua Vergueiro, 2355 – Liberdade, São Paulo 01504-001, SP, [AQ01] Brazil ([email protected]). Copyright © 2017 Academy of Geriatric Physical Therapy, APTA.

Copyright © 2017 Academy of Geriatric Physical Therapy, APTA. Unauthorized reproduction of this article is prohibited.

JGPT-D-17-00026.indd 1

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Research Report postural control system using a different postural adaptation strategy in comparison to young adults to diminish the risk of losing balance and falling. A better understanding of the adaptation of postural control in older adults during tasks with differing levels of complexity may contribute to the development of new strategies for the prevention of falls in this population. This assumption can be tested by quantifying sway velocity in the anterior-posterior (AP) and medial-lateral (ML) directions during quiet standing on a force platform, which provides valid data on the quality of upright postural control, especially among older people, since greater sway velocity is typically used to differentiate postural control between different age groups16 and is predictor of falls among older individuals.17,18 Moreover, a strong association has been found between lower cognitive ability and poorer balance performance.19 Mean sway velocity is also considered the most reliable measure in trials in comparison to traditional stabilometric parameters (maximum amplitude, root mean square, frequency, and entropy).20,21 Given these observations, the hypothesis tested herein is that the aging process alters adaptive postural control responses to complex tasks. Thus, the aim of the present study was to evaluate the adaptation of the postural control system in response to different degrees of task complexity in physically inactive older women in comparison to physically inactive young women.

METHODS Participants A cross-sectional study was conducted with 27 young and 27 older adult sedentary women recruited from Nove de Julho University and locations near the university. This study received approval from the local institutional review board (number: 394875/2011), and all participants signed a statement of informed consent prior to the data collection process. The sample size was calculated based on a pilot study with 9 young (mean age, 23.02 years; standard deviation [SD], 4.43 years) and 9 older (mean age, 68.14 years; SD, 4.43 years) healthy physically inactive women using the same experimental conditions described in the Procedures subsection. The calculation was performed considering the difference in body sway in the AP and ML directions, α = 0.05 (5% chance of a type I error) and 1-β = 0.90 (text power of the sample). The difference in sway velocity in the ML direction with eyes closed (0.67 [SD, 0.02] cm/s and 0.79 [SD, 0.17] cm/s in the groups of young and older women, respectively) led to the largest sample size (27 individuals per group). The calculation was performed using G*Power software, based on Faul et al.22 Healthy young women aged 20 to 30 years and healthy older women aged 60 to 80 years were included in the study. All participants were physically inactive, had no cognitive impairment or vestibular disorder, and agreed to participate in the study. Physically active women, those with 2


joint disease (arthritis or arthrosis), diabetes, vestibular disorder (dizziness), neuromuscular diseases, orthodontic, or joint prostheses and those undergoing physiotherapeutic treatment were excluded. Information on physical activity was collected using the short form of the International Physical Activity Questionnaire. The version used in the present study contains 7 questions and is the same as that used in a 12-country reliability and validity study.23 The questions were based on the frequency and duration of physical activity, including walking, moderate and vigorous physical exercise, and sitting time in the previous week. Individuals were considered inactive if their participation in physical activity was less than 150 minutes per week.24

Outcome Measure Mean sway velocity in the AP and ML directions was the outcome and used to assess the complexity of postural control.

Instrumentation A force plate (BIOMEC 400 v1.1, EMG System Ltd) (dimensions: 1 × 1 m) composed of 4 load cells with a sampling frequency of 100 Hz was used to measure postural control.

Procedures Figure 1 displays the flowchart of the study. The participants were instructed to stand quietly directly on the force plate or on a foam rubber mat measuring 40 × 600 × 50 mm positioned on the force plate, with the arms alongside the body, barefoot, feet approximately shoulder-width apart and heels aligned. On the tests performed with the eyes open, the participants were instructed to keep their eyes fixed on a circular target (5 cm in diameter) at eye level placed at a distance of 2 m. Six different test condi-

Figure 1. Flowchart of the study.

Volume 00 • Number 00 • 000 2017 Copyright © 2017 Academy of Geriatric Physical Therapy, APTA. Unauthorized reproduction of this article is prohibited.

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Research Report tions were considered: eyes open (EO) and eyes closed (EC) on the force plate; eyes open and eyes closed standing on the foam (EOF and ECF, respectively), and during an auditory-visual task (AV) on the force plate and on the foam rubber mat (AVF). For the auditory-visual task, an Archimedean spiral was placed at a distance of 2 m at eye level (Figure 2). A horizontal line and a vertical line (forming a cross) were drawn in the spiral. The different intersection points between the lines of the spiral and the horizontal and vertical lines in the figure were marked with circles of different colors for each level of the spiral. During the data collection, the participants were asked to gaze at the outermost marking of the spiral (dark blue dot). Each beat of a metronome adjusted to a rate of 60 beats per minute served as the guide for the participants to direct their gaze to the subsequent marking until reaching the central point (light blue point), at which time they were instructed to return their gaze to the starting point (dark blue dot) and continue the visual activity until the test was terminated. During the tests, the individuals were instructed not to move their heads as they moved their gaze. Three 40-second collections were made for each condition (total of 18 collections). To avoid possible effects of fatigue, the volunteers were instructed to rest on a chair for 2 minutes between conditions (total of 6 collections).

Signal Processing The data were filtered using a Butterworth low pass filter with a cutoff frequency of 10 Hz. The initial 10 seconds of each collection was disregarded since they may reflect only the effects of the initial postural adaptation. The sway

velocity in the AP and ML directions was calculated considering the total distance travelled divided by time (cm/s).25

Estimated Task Cost The task cost was estimated based on the concepts of postural and attentional control. When 2 tasks (postural and attentional control) are performed at the same time (dual task) and require more than the total amount of available resources, a task cost (decline in the performance on one or both tasks) occurs.26 In practical terms, when the complexity of the postural task is increased by a dynamic surface and surrounding conditions, the performance on the concurrent task, postural task, or both is degraded more in older adults compared with young adults.26 To estimate the cost of the different test conditions for postural control, the EO condition was considered a simple task and the EC, EOF, ECF, AV, and AVF tests were considered complex tasks. The task cost was calculated as follows: task cost = ([simple task − complex task]/simple task)] × 100.27 Negative values were interpreted as a higher task cost for postural control and positive values were interpreted as a lower cost.

Statistical Analysis The Kolmogorov-Smirnov test was used to test the normality of the data distribution and data transformation was applied as needed. Differences between groups were tested using a 2-way analysis of variance with Bonferroni corrections. A general linear model with repeated measures was used, which included the intergroup factor (age: young or older adult) and intragroup factors (visual conditions: eyes open or closed; surface: directly on force plate on foam place on force plate). The paired t test was used to determine differences between conditions (tasks) within groups. The unpaired t test was used to compare differences between groups. Demographic information and study outcomes were reported as mean and SD values. The results of the intergroup comparisons were reported as estimates with respective 95% confidence intervals. A bidirectional P value less than α = 0.05 was considered indicative of statistical significance.

RESULTS The Table displays the demographic characteristics of the sample and outcomes during the tasks. Significant differences between groups were found for demographic characteristics. The older women had greater body weight, less height, higher body mass index scores, and lower levels of schooling compared with the younger women. All participants spent less than 150 minutes a week involved in physical activities.

Differences in Postural Control and Task Cost Within Groups Figure 2. Participant standing on the force plate performing the test with the Archimedean spiral demarcated at the points of intersection with a horizontal and vertical line. Color aided guide during testing. Journal of GERIATRIC Physical Therapy

On the AP axis, sway velocity increased in both groups when the task conditions were altered (Table). Compared with EO, significant increases in sway velocity were found for the conditions of EOF (P < .001 in the young group; P = .005 in the older group), EC (P < .001 in the young group; P =



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Research Report Table. Baseline Demographics and Study Outcomes Variables

Young Women (N = 27)

Older Women (N = 27)

Mean Difference Between Groups (95% CI)

22.1 (4.4)

68.5 (6.4)

46.4 (43.0 to 49.7)a

Demographics Age, mean (SD), y Weight, mean (SD), kg

58.6 (9.3)

68.6 (12.5)

Height, mean (SD), m

1.6 (0.1)

1.5 (0.1)

0.1 (−0.1 to −0.1)a

Body mass index, mean (SD), kg/m2

21.9 (2.7)

29.0 (4.8)

6.8 (5.0 to 8.6)a

Years of education, mean (SD), y

13.3 (0.8)

6.3 (3.8)

−7.0 (−-8.6 to −5.5)a

104.1

95.6

−8.5 (−15.9 to −1.1)

EO, mean (SD)

0.5 (0.2)

0.8 (0.3)

0.3 (0.2 to 0.4)a

EOF, mean (SD)

0.5 (0.2)b

0.9 (0.4)b

0.3 (0.2 to 0.4)a

EC, mean (SD)

0.6 (0.2)b

0.9 (0.3)b

0.3 (0.2 to 0.4)a

(0.2)b

(0.5)b

0.4 (0.2 to 0.3)a

Time physical activity, min/wk

9.9 (4.7 to

[AQ03]

16.1)a

Postural sway velocity, cm/s Anterior-posterior axis

ECF, mean (SD)

0.6

1.0

AV, mean (SD)

0.5 (0.1)

0.7 (0.3)

0.3 (0.2 to 0.3)a

AVF, mean (SD)

0.5 (0.2)

0.8 (0.3)

0.3 (0.2 to 0.4)a

EO, mean (SD)

0.5 (0.1)

0.7 (0.2)

0.2 (0.1 to 0.2)a

EOF, mean (SD)

0.5 (0.2)b

0.7 (0.2)b

0.2 (0.1 to 0.2)a

EC, mean (SD)

0.5 (0.1)b

0.7 (0.2)

0.2 (0.1 to 0.2)a

(0.2)b

(0.2)b

0.2 (0.1 to 0.2)a

Medial-lateral axis

ECF, mean (SD)

0.5

AV, mean (SD)

0.5 (0.1)b

0.7 (0.2)b

0.2 (0.1 to 0.3)a

(0.1)b

(0.2)b

0.2 (0.1 to 0.0)a

AVF, mean (SD)

0.6

0.7 0.7

Abbreviations: AV, auditory-visual task; AVF, auditory-visual task standing on foam; CI, confidence interval; EC, eyes closed task; ECF, eyes closed standing on foam task; EO, eyes open task; EOF, eyes open standing on foam task; SD, standard deviation. aSignificantly different between young and older adults bSignificantly different from the control condition (EO) for the anterior-posterior or medial-lateral direction.

.02 in the older group), and ECF (P < .001 in both groups). However, no changes were found under the conditions of AV or AVF compared with EO in either group. On the ML axis, sway velocity also increased in both groups when the task conditions were altered. Compared with the EO condition, significant increases were found for the conditions of EOF (P < .001 in the young group; P = .005 in the older group), EC (P = .02 in the young group), ECF (P < .001 in both groups), AV (P < .001 in the young group; P = .005 in the older group), and AVF (P < .001 in both groups).

Differences in Postural Control and Task Cost Between Groups The Table displays the mean differences in sway velocity between groups with 95% confidence intervals. The findings indicate that the group of older women demonstrated increased sway velocity (cm/s) along both the AP and ML axes on all tasks. With regard to the task cost, no significant differences between groups were found in either the AP or ML direction (Figure 3). 4


DISCUSSION The changes in sway observed from center-of-pressure excursion measures may represent functional adaptations made by the postural control system to maintain balance.28 However, the hypothesis that the adaptive response of postural control would be different in young and older women engaged in tasks with different levels of complexity was not confirmed in the present study. Considering the task cost associated with task complexity (eg, EO vs EOF), the responses in postural sway velocity were similar for both groups. In other words, both groups exhibited similar postural control adaptations when task complexity was increased. However, the young women outperformed (lower sway velocity) the older women on all tasks, regardless of the complexity of the task. These results are similar to data described in previous studies investigating postural control in young and older people on different tasks, which found an increase in body sway associated with the age-related decline in postural control.13,29 In the present study, postural sway velocity increased in both groups when the complexity of the task was elevated


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Research Report

Figure 3. Mean and standard deviation of the task cost calculated from the oscillation velocity in anterior-posterior and medial-lateral directions for young and older women. Negative values were interpreted as indicating a higher cost for postural control and positive values as a lower cost. AV indicates auditory-visual task; AVF, auditory-visual task standing on the foam; EC, eyes closed task; ECF, eyes closed standing on the foam task; EO, eyes open task; EOF, eyes open, standing on the foam task.

with the withdrawal of visual feedback and the use of a foam rubber mat. This confirms that changes in the somatosensory system exert a direct influence on the postural control system regardless of age. The fact that the older women demonstrated significantly greater sway in comparison to the younger women suggests that the aging process can affect the sensory systems and provoke a decline in the postural balance control system. These findings are in agreement with data described in previous studies examining balance during quiet standing, which found an increase in body sway with a deficit of information from any sensory system: visual, vestibular, or somatosensory.29-31 A previous study found that older adults with and without a history of falls demonstrated greater sway in the AP direction compared with healthy young participants, which was also reflected in increased muscle activity in the lower limbs (specifically, the tibialis anterior muscle and biceps femoris muscle). This increased muscle activity was related to a decline in the ability of the postural control system to maintain an adequate upright posture in older adults.32 The previous findings mentioned earlier combined with the outcomes of the present study confirm the occurrence of age-related degenerative changes in the somatosensory system in older adult women.2,32 The clinical relevance of this information is that age-related negative alterations in postural control, as identified and interpreted using force plate variables such as those employed in the present study, may be associated with an increased risk of falls among older adults.17 Indeed, greater sway velocity in the AP and ML directions has been described as a strong predictor of falls.33 The task cost analysis demonstrated that both groups adapted to the increase in task complexity in a similar manner (no significant differences between the groups). Thus, although aging may result in limitations (increased instability) with regard to the ability of the somatosensory system to respond to different task conditions, the process of recruiting the sensory systems (visual and somatosensory) and other strategies for maintaining body stability do not differ significantly between young and older Journal of GERIATRIC Physical Therapy

individuals. Therefore, the results regarding different levels of task complexity in physically inactive older women do not support the earlier hypothesis that older individuals optimize their postural control system by using a different posture adaptation strategy in comparison to young adults to diminish the risk of falls. Moreover, despite the evidence that the aging process requires greater reliance on visual feedback for the maintenance of postural control,34 this was not evident in relation to postural adaptation, as no significant differences between groups were found for the 3 different visual conditions tested (EOF, EC, and ECF) (Figure 3). This finding is consistent with the results of previous studies35,36 and indicates that older adults adapt to changes in visual input in a similar way to younger adults. The present findings contribute new knowledge regarding the adaptation mechanisms involved in postural control in healthy young and older adults. However, further investigations addressing the mechanisms underlying the adaptation of postural control involving tests with different levels of complexity including perturbations, adaptations, and sensory reweighting mechanisms may contribute to a better understanding of postural control in older individuals. As falls are a major problem in older adults2,37 and can lead to serious injuries as well as a reduction in life expectancy,38 a better understanding of postural control adaptations and the task cost associated with task complexity could assist in clinical decision-making regarding the choice of intervention methods aimed at preventing or slowing the decline in postural control among frail populations, especially older adults. Such efforts could result in a reduction in the risk of falls and an increase in life expectancy. An important issue to raise is that the results of the present study refer to sedentary older women. In general, physically active individuals have better postural control than sedentary individuals regardless of age.39 A recent literature review described 2 main types of activity that have differential effects on balance control in healthy older adults: strength training to improve dynamic balance



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Research Report and proprioceptive activities to improve static balance.40 Thus, physical activity, especially when considered in view of falls and instability, is a crucial issue for the geriatric population.41

CONCLUSIONS In the present study, the adaptive response of postural control to different levels of task complexity did not differ between physically inactive young and older women. However, the physically inactive older women demonstrated greater sway velocity compared with the young women, which suggests an age-related decline in the balance function.

ACKNOWLEDGMENTS This study is supported by the Universidade Nove de Julho (UNINOVE, Brazil) and the Brazilian fostering agency Conselho Nacional de Desenvolvimento Conselho Nacional de Desenvolvimento Cientifico e Tecnológico (CNPq: Process no. 447728/2014-8).

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AUTHOR QUERIES TITLE: Age-Related Changes in Postural Control in Physically Inactive Older Women AUTHORS: Juliana Teles Tavares, Daniela Aparecida Biasotto-Gonzalez, Nárlon Cássio Boa Sorte Silva, Frank Shiguemitsu Suzuki, Paulo Roberto Garcia Lucareli, and Fabiano Politti [AQ00]: Please check if authors name are correctly captured for given names (in red) and surnames (in blue) for indexing after publication. [AQ01]: Institutional address rather than personal is preferred in the correspondence details. Please check. [AQ02]: Please verify the disclosure statement. [AQ03]: Please note that values in the Table have been rounded to the tenth place as per the style sheet.


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