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GAIPOS-4406; No. of Pages 4 Gait & Posture xxx (2015) xxx–xxx
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Gait & Posture journal homepage: www.elsevier.com/locate/gaitpost
Older adults prioritize postural stability in the anterior–posterior direction to regain balance following volitional lateral step Shaun Porter, Julie Nantel * School of Human Kinetics, Faculty of Health Sciences, University of Ottawa, ON, Canada
A R T I C L E I N F O
A B S T R A C T
Article history: Received 11 August 2014 Received in revised form 19 January 2015 Accepted 21 January 2015
Background: Postural control in the medial–lateral (ML) direction is of particular interest regarding the assessment of changes in postural control, as it is highly related to the risk of falling. Objective: To determine the postural strategies used to regain balance following a voluntary lateral step and compare these strategies between young and older adults. Methods: Sixteen older adults (60–90 years) and 14 young adults (20–40 years) were asked to stand quietly for 30 s, walk in place and then take a lateral step and stand quietly (30 s). Balance Post was divided into 10 s intervals. Center of pressure displacement (CoP) and velocity (VCoP) in the anterioposterior (AP) and ML directions were analyzed. Results: In both groups, CoP and VCoP in AP and ML increased in Post1 compared to Pre (P < 0.001). Dissimilar to young adults, VCoP-Post2, Post3 ML were larger than Pre (P = 0.01) in older adults. Age correlated with all VCoP (Pre and Post) in both ML (P < 0.05) and AP directions (P < 0.01). Conclusions: Dissimilar to young adults, older adults use different postural strategies in ML and AP directions and prioritized postural stability in the AP direction to recover balance after completing a lateral step. In the ML direction, older adults took up to 30 s to regain balance. Considering that age was related to larger CoP displacement and velocity, the AP strategy to recover postural balance following a lateral step could become less efficient as older adults age and therefore increasing the risk of falls. ß 2015 Elsevier B.V. All rights reserved.
Keywords: Aging Postural balance Falls Lateral step Postural strategies
1. Background The ability to control postural balance during activities of daily living plays an essential role in the functional mobility and independence of older adults. Deficits in postural stability are seen in different conditions including stroke, type II diabetes, Parkinson’s disease, but also in older adults. This often results in larger center of pressure (CoP) displacement and velocity, in quiet standing [1–6], and, in the use of distinctive postural strategies following large external perturbations [7–10]. One of the most common strategies used to recover balance after a large perturbation is to take a step. While this strategy is common to both younger and older adults, older adults are more likely to use a multi step strategy in order to fully regain balance after such a perturbation [7,9]. However, this multi step strategy increases the
* Corresponding author at: School of Human Kinetics, Faculty of Health Sciences, University of Ottawa, 125 rue Universite´, Pavillon Montpetit, MNT 353, Ottawa, Canada K1N 6N5. Tel.: +1 613 562 5800x4025; fax: +1 613 562 5497. E-mail address:
[email protected] (J. Nantel).
risk of tripping and falling, primarily in the medial–lateral (ML) direction [7,8,11–13]. Postural instability in the ML direction is particularly important, as it is associated with an increased risk of falling [7,8,11,12,14]. When assessing age-related variability in postural control using a rapid voluntary forward stepping task, Kurz et al. [15] reported greater CoP variability in the ML direction both during and immediately following stepping in older adults compared to younger adults. Older adults also needed more time to complete the stepping task; however, those who were able to complete the task rapidly demonstrated better control of balance in the ML direction while performing the task. Age also affects the type and completion of postural strategies to complete a voluntary lateral step compared to young adults. Sparto et al. [16,17] reported more variable postural adjustments and a longer latency period prior to stepping in older adults compared to younger adults. Furthermore, older adults with a history of falls were more likely to make use of two or more postural adjustment strategies to execute the task [16,17]. The present study will determine the postural strategies used to regain balance following a voluntary lateral step and compare these strategies between young and older adults. We expect older
http://dx.doi.org/10.1016/j.gaitpost.2015.01.021 0966-6362/ß 2015 Elsevier B.V. All rights reserved.
Please cite this article in press as: Porter S, Nantel J. Older adults prioritize postural stability in anterior–posterior direction to regain balance following volitional lateral step. Gait Posture (2015), http://dx.doi.org/10.1016/j.gaitpost.2015.01.021
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GAIPOS-4406; No. of Pages 4 S. Porter, J. Nantel / Gait & Posture xxx (2015) xxx–xxx
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adults to take more time to recover postural balance following the lateral step and use different postural strategies compared to younger adults. 2. Methods
to account for the differences between young and older adults and the time intervals (Pre, Post1-Post3). Holm-Bonferroni procedures were used when necessary. Relationships between age and measures of postural stability were assessed using Pearson correlations. Statistical level of significance was set at P < 0.05. 3. Results
2.1. Participants
3.1. Center of pressure displacement and velocity: Pre versus Post
Convenience sample of thirty subjects: 14 healthy younger adults (mean: 25.4, sd: 6.5, min: 20, max: 42 years, 14 women) and 16 healthy older adults (mean: 73.0, sd: 8.5, min: 60, max: 90 years, 12 women) participated in the study. Subjects were excluded if they reported any impairment with the potential to interfere with balance. The study was approved by our Institutional Review Board. Task: Participants were asked to take part in a motor task in order to assess their postural control before and following a voluntary lateral step. First, participants stood quietly for 30 s with their feet at a comfortable width. Following a visual cue displayed on a monitor 1 m in front of them, participants walked in place at a comfortable pace for 60 s. They were then given another visual cue prompting them to transition from stepping in place to standing quietly for 30 s by stepping laterally on a force platform positioned on their dominant side. The lateral step was initiated with the dominant leg. This transition was completed at a comfortable pace and the task was performed barefoot and repeated three times. The stepping in place task was included in the protocol, as we wanted the lateral step to be preceded with a dynamic task that would resemble a walking activity rather than transitioning from a quiet standing position. Thus, besides controlling the lateral movement of the trunk, participants had to control the arrest of arm motion in the sagittal direction. Ground reaction forces and moments were collected using two force platforms (Kistler, Winterthur, Switzerland) recording at a sampling frequency of 200 Hz and filtered with a zero-lag fourthorder Butterworth filter with a 10 Hz cut-off frequency. The weighted sum of the time-varying position of the CoP under each foot was calculated using the orthogonal forces and moments as recorded by the force plates. The CoP displacement and mean velocity (VCoP) were calculated before (CoP-Pre) and after (CoPPost) the lateral stepping, and reported as the root-mean-square displacement amplitude (in mm) of CoP and VCoP (mm/s) in both the anterio-posterior (AP) and ML directions. The onset of the ‘‘recovery’’ period (CoP-Post) was defined when both feet were located on the force platform. The CoP-Post was divided into three 10 s intervals (CoP-Post1 to CoP-Post3) for the assessment of restabilization strategies. 2.2. Statistics The CoP and VCoP before and after the stepping in place task (averaged over the three trials) were compared between groups and between time intervals using Two-Way Mixed Design ANOVAs
In both older and younger participants, both CoP (P < 0.01) and VCoP (P < 0.001) Post and Post1 increased compared to Pre values in the ML and AP directions (Table 1). In young participants, CoP-Post2 and Post3 decreased compared to Pre (P < 0.01), while VCoP-Post2 and Post3 returned to VCoP-Pre values in both directions. Dissimilar to younger participants, CoP-Post2 and Post3 did not go below Pre values in the older adult group, with the exception of CoP-Post3 in the AP direction (P = 0.01). Also unlike the young adult group, older adults did exhibit larger VCoP-Post2 and Post3 in the ML direction compared to Pre (P = 0.01). 3.2. Center of pressure displacement and velocity: young versus older adults and correlations with age CoP-Post2 (P = 0.01) and VCoP-Pre in the AP direction as well as all VCoP (Pre and Post1-3, ML and AP) were larger in older adults compared to young adults (P < 0.05). Age showed moderate correlations with all the VCoP measures in both AP (r = 0.53–0.62, P < 0.01) and ML (r = 0.36–0.48, P < 0.05) directions (Table 2). As for CoP rms displacement, only CoP-Pre (r = 0.37) and CoP-Post1 (r = 0.38) in the ML direction and CoP-Post2 (r = 0.41) in the AP direction reached the level of significance (P < 0.05).
4. Discussion The objective of our study was to compare the postural strategies used to regain balance following a voluntary lateral step in young and older adults. Older and younger adults used different postural strategies to regain balance after taking a lateral step, and older adults displayed larger CoP velocity in the ML direction for up to 30 s. During the first 10 s post step, both groups showed expectedly larger CoP displacement and velocity due to the transition from the dynamic to the static task. Surprisingly, in the last 20 s post step, the CoP displacement in the younger adult group fell below baseline (Pre) values, while velocity returned to normal. This drastic reduction in CoP displacement may permit the control of CoP velocity in both directions, allowing for a prompt restabilization of center of mass (CoM). In line with these results, Memari et al. [18] reported large and rapid consecutive postural adjustments in young individuals following a step. They suggested that this strategy may contribute to efficiently stabilize balance after the contact of the foot with the ground. In the present study, participants were asked to adopt a comfortable foot placement before and after taking the lateral step. Consequently, the smaller CoP displacement in the last 20 s may have resulted from the participants’ selection of a smaller base of support. However, the similar reduction in CoP displacement in the AP direction strongly suggests that older adults adopted this strategy to counteract the large CoP displacement and velocity in the first 10 s post step.
Table 1 Root-mean-square CoP displacement (mm) and velocity (mm/s); comparisons between and within groups. Young (n = 14) CoP ML Pre Post Post1 Post2 Post3 y z
2.0 3.3 3.9 1.5 1.3
(0.6) (1.1)z (1.5)z (0.8)z (0.6)z
Older adults (n = 16) CoP AP 3.3 4.7 5.1 2.4 2.4
(1.1) (1.5)z (1.8)z (1.1)z (1.1)z
VCoP ML
VCoP AP
CoP ML
CoP AP
VCoP ML
VCoP AP
2.8 5.1 8.0 3.1 2.8
Mean (SD) 4.1 (1.0) 5.9 (1.3)z 8.3 (1.8)z 4.2 (1.3) 4.1 (1.0)
2.5 4.6 5.2 2.7 2.5
3.7 5.3 5.8 3.3 2.8
3.5 7.1 11.1 4.7 4.3
5.6 7.9 11.0 6.0 5.6
(0.6) (1.4)z (2.3)z (1.2) (1.0)
(0.9) (2.4)z (2.4)z (2.2) (2.4)
(0.8) (1.2)z (2.0)z (1.0)y (1.2)z
(1.4) (2.8)y,z (4.8)y,z (2.3)y,z (2.2)y,z
(1.7)y (2.3)y,z (3.5)y,z (1.8)y (1.7)y
Older adults different from young adults (P < 0.05). Different from Pre (P < 0.05).
Please cite this article in press as: Porter S, Nantel J. Older adults prioritize postural stability in anterior–posterior direction to regain balance following volitional lateral step. Gait Posture (2015), http://dx.doi.org/10.1016/j.gaitpost.2015.01.021
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GAIPOS-4406; No. of Pages 4 S. Porter, J. Nantel / Gait & Posture xxx (2015) xxx–xxx Table 2 Correlations between age and CoP velocity in both ML and AP direction. N = 30
R values P values y
3
5. Conclusions
CoP velocity medial–lateral
CoP velocity anterior–posterior
Pre
Post1
Post2
Post3
Pre
Post1
Post2
Post3
0.39 0.04y
0.48