A cross-sectional study to investigate dominant leg balance performance in healthy elderly individuals| JOURNAL OF GERONTOLOGY AND GERIATRICS

Abstract

Background. Examining underlying balance mechanism of the elderly can help identify their Achilles’ heel of
balance system. The research aim was to investigate the dominant leg balance characteristics of a sample of
older adults while being challenged by sensory inputs and performing dual task.
Methods. This study was performed on 20 healthy elderly subjects during four conditions of one-leg standing
with different levels of difficulty including: “open eyes”, “dual task with open eyes”, “closed eyes” and “dual
task with closed eyes”. Forceplate was used to evaluate postural control during standing on dominant leg
measuring “Area” and “Velocity” as the dependent variables. Auditory Stroop task was used to simulate performing a secondary activity (dual task). Using Bonferoni post hoc test, Repeated Measurement Analysis of
Variance was executed to find the differences between the conditions.
Results. Comparisons showed significant differences of “Area” [F (3, 13) = 10.143, p = 0.001] and “Velocity”
[F (9, 13) = 9.692, p = 0.001]. Bonferoni test revealed that all four conditions had significant differences except
two pairs including (a) “open eyes” with “dual task with open eyes”, and (b) “closed eyes” with “dual task with
closed eyes” (p > 0.05).
Conclusions. Results indicated that participants adopted a strategy to increase “Area” and “Velocity” during
the challenge of standing on dominant leg with closed eyes. This is their tactic to maintain balance during the
elimination of visual input. Exploring balance strategy would have important implications for developing long
term fall prevention programs.

BACKGROUND

Evaluating balance performance has become a favorite topic that can help identify Achilles’ heel of the elderly balance mechanism so as to address their health care delivery systems. Balance performance is an essential issue in human motor control influencing most fields of daily living including work, leisure, and self-care. There are different laboratory systems that assist examiners to evaluate such performance. Forceplate seems to be one of the most suitable instruments that assess balance ^{1 2}. As balance is known to be the inevitable and crucial part of doing ordinary tasks of everyday life ³, it is essential to have a trustworthy assessment instrument. Objective assessment of postural stability can be done by Forceplate ⁴. Forceplate allows balance analysis and enables postural control stability monitoring through measurements of sway, and it is proved to have academic and clinical advantages.

In order to investigate postural stability, Forceplate technology provides researchers with informative center of pressure (COP) variables such as “Area” and “Velocity” used in this study. Until now, one single or more than one Forceplate ⁵ has been used in different studies for healthy ⁶, athletes ⁷, patients populations ^{8 9} or balance-impaired elderly adults ¹⁰ during standing ¹¹, walking ⁶ or jumping performance ^{2 12}. To quantify the balance performance, people were studied during double leg ¹³, feet together ¹⁴, one-leg standing ^13-17, tandem ^{4 8}, or standing on Forceplate with unstable surface ¹⁸. Furthermore, studies with sensory manipulations ¹⁹ such as open and closed eyes ^{13 14} were also conducted.

Balance is supported by inputs from somatosensory, visual and vestibular systems along with neuromuscular, skeletal and cognitive sources. Dominant and non-dominant leg performance are prerequisite factors for studying balance performance. Some researchers studied balance during one-leg stance with Forceplate ^{14 16} or without it ^{20 21}, some have recruited dominant leg ¹³ or preferred foot ¹⁵. However, according to existing evidence little attention has been paid to investigate each lower limb contributions to balance capacity ²². So, the present research is mainly focused on the dominant limb contributions so as to explore more about its substrate balance strategy during a number of challenging conditions.

Dual task performance is also thought to help researchers to explore more about the interaction of cognition and balance. There are variations in response to dual task which are linked to postural ^23-27 or the dual task nature ^{28 29} and their level of difficulty. For instance, Vuillerme (2004) ¹⁸ reported dual task cost (i.e. the interference of one task in doing another one) even in young gymnastic experts during one leg standing. However, having cost is not always the case when performing dual tasks ^30-32. Elderly adults’ balance was also a major target in many balance studies ^33-36. While some believe in age-related decline of elderly balance performance during dual task ³⁷, others do not think so ^{32 38}.

Visual input is another important and essential factor in the area of balance research. Therefore, visual input in elderly adults is considered as one important issue that is useful to be investigated more. Consequently, this research was conducted to examine the effect of visual input and dual task on healthy elderly balance performance and generate fresh insight into standing on dominant lower extremity. Characterization of dominant leg is important for our understanding of maintaining upright one leg standing. It is suggested that using this procedure would be useful as a challenge in selection of high risk individuals in the process of designing prevention protocols ¹². This study aimed to contribute to this growing area of research by exploring the balance strategy of the elderly individuals. Therefore, this study made a major contribution to research on dominant leg performance by demonstrating change trend of center of pressure (COP), and it contributed to a deeper understanding of older adults’ responses during simulated difficult circumstances.

METHODS

PARTICIPANTS

Twenty healthy non-institutionalized elderly subjects (male = 14, female = 6, age = 61.15 ± 1.95 years, height = 166.9 ± 7.07 centimeters, weight = 73.9 ± 8.89 kilograms, with body mass index (BMI) average factor of 26.6 (SD = 2.8) participated in this cross-sectional study. The participants’ Mini-Mental State Examination (MMSE) mean score was 28.25 (SD = 1.97). All the participants’ dominant leg were the right ones.

The inclusion criteria includes being independent with an active life style. Not using sedative drugs, having no visual, auditory, verbal and sensory problems such as those secondary to diabetes were checked based on their medical history prior to the study. Participants who had any current lower extremity, trunk fractures, dislocations and surgery during the last six months were excluded. They must be free of any lower extremity injury that would limit the ability to maintain balance on one foot. Any problems during the data gathering process and recording such as fatigue, pain, dissatisfaction, fear of fall and instrumental deficit, which could cause the trial performance to be failed, were monitored.

PROCEDURES AND INSTRUMENTATION

This study consisted balance assessments of 4 trials performed on a 90” x 90” series Forceplate (Kistler -Switzerland), with sampling rate of 400 Hz and sensitivity of 10. The tasks included maintaining balance under varying stance conditions: single standing on dominant leg with open eyes on Forceplate (SO), single dominant leg standing with open eyes performing dual task (SOD), single dominant leg standing with closed eyes on Forceplate (SC), and single dominant leg with open eyes performing dual task (SCD).

Each trial was 20-seconds long and required the participant to maintain balance with standing on their dominant legs motionlessly. Each condition was separated by a five-minute rest interval preventing fatigue ³. During one leg standing, the raised leg should not have any contact with Forceplate. The participants also were not allowed to jump in place and if they behaved out of standing protocol, the trial was considered failed. One major concern and percussion was to provide them with suitable control protection against unpredictable fall during one leg standing.

After describing the test procedure to the participants, they filled in the consent form, as Williams (2017) considered familiarization an inevitable and important part of test procedures ⁴. The trial conditions were performed with random order following completion of familiarization. Forceplate was unloaded and calibrated before each trial to guarantee accurate data gathering. In this study, dual task was the auditory Stroop task. During this task ‘high’ and ‘low’ words were played back with low and high tone pitch. The participants were required to answer by mentioning the tone regardless of words meaning itself. Wireless earphone and microphone (LEM-NP10, Taiwan) were used to execute auditory Stroop task. R2015a Matlab program and Microsoft Office Excel 2013 were also used.

Research setting was at University of Social Welfare and Rehabilitation Sciences (USWRS) laboratory setup. In the context of this sort of setup, closed eyes condition is believed to simulate real life situations in which people encounters difficulty accessing their visual input. Moreover, the Stroop task is somehow thought to detect reactions during performing dual task. This research project was approved by USWRS’s ethical committee.

MEASUREMENTS

Objective outputs of postural sway in this study were the dependent variables of COP; “Area” (CM²) and “Velocity” (CM/S), with higher values indicating worse balance. “Area”, the biomechanical stability parameter of overall COP displacement in all directions, was considered dependent variable by the means of which balance assessment was done in this study in four mentioned conditions. “Velocity” is also another parameter of COP in which displacement is considered along with time and is an index of postural control.

DATA ANALYSIS

Kolmogorov-Smirnov test was used to examine the normality and it showed the normal distribution of the data. Repeated measure analysis of variance were used for statistical analysis by the means of IBM SPSS statistics 20. The reference P-value was considered 0.05 to prove the significant differences. The Bonfferoni post-hoc analyses was used to define exact different conditions.

RESULTS

During the test procedure there were some participants who were unable to accomplish their balance performance trials. One failed to maintain balance during dual task condition with open eyes, two fell when their eyes were closed during performing single task, and one attempt was in vain at dual task condition with closed eyes. Kolmogorov-Smirnov test reported the “Area” and “Velocity” variables to be normally distributed in all conditions (p > 0.05). Mean Area (Fig. 1) and its standard deviation are presented as below: SO [11.84 (11.01)], SOD [10.52 (10.21)], SC [44.75 (28.702)] and SCD [39.98 (39.53)]. Repeated measurement analysis of variance results showed that there were significant differences between conditions mean Area [F(3,13) = 10.143 p = 0.001]. Further analysis of paired comparisons have also detected the exact two conditions between which statistically significant differences existed (Tab. I).

Postural variable amounts are shown in Figure 1. This line graph reveals “Area” change pattern during four conditions of adding and removing visual input and dual task. Looking at the graph, it can be said that a hidden pattern of reactions and changes is evident in that Z-like fashion. There is a marginal decline of “Area” displacement from the SO condition to SOD condition. The least mean is related to the SOD trial. A sharp rise is displayed from SOD condition to the SC condition. This upward trend is statistically significant manifesting that COP displacement amount and its velocity would surge when visual input is omitted. The amount of “Area” in closed eyes conditions were much more than open eyes conditions and its amount hits the highest point in single task with closed eyes condition. There is again a slight decrease from SC trial to SCD trial. However, mean “Area” in closed eyes conditions were significantly higher than means in open eyes conditions, regardless of dual task performance.

Mean Area (Fig. 2) and its standard deviation are presented as below: SO [7.3 (4.5)], SOD [7.1 (2.7)], SC [16.8 (8.1)] and SCD [15.4 (8.8)].

Repeated measurement analysis of variance results showed that there were significant differences between conditions mean “Velocity” [F (9, 13) = 9.692, p = 0.001]. Further analysis of paired comparisons have also detected the exact two conditions between which statistically significant differences existed (Tab. II).

DISCUSSION

According to our findings, the four mentioned test conditions used in this study made the participants control their center of gravity within their base of support. Some participants were unable to maintain their balance during some conditions with different levels of difficulty owing to the challenging nature of one leg standing. Those who accomplished their trials showed increased sway during closed eye condition. Undoubtedly, it can be inferred that visual input deprivation effect is more dominant than dual task effect on the “Area” and “Velocity” parameter in this study. With closed eyes condition standing on dominant limb, there would be a threat for centre of gravity to go beyond the base of support and it would be harder to restore COP, thus leading to an increase in “Area” and “Velocity” subsequently. It also conveys the importance of this input corporation and contribution to postural control and the countless dependency on that.

One of the concerns was that the higher “Area” and “Velocity” variables were, the more unsteady the participants were during the test (indicating greater instability during closed eyes conditions). These findings are consistent with the literature proving the inevitable effect of visual input on postural stability ^{17 39 40}. Previous studies have shown increased “Area” ^{39 40} and “Velocity” ⁴⁰ of COP displacements in blindfolded tasks which is in complied with the results of this study. According to Zeynalzadeh et al.’s study, whenever dual task and decreased visual input occur at the same time, the adopted strategy of increasing “Velocity” would emerge identifying the Achilles’ heel of the elderly during double leg standing ¹¹.

In the case of standing on non-dominant leg in the elderly, weight bearing on only one leg is a difficult mission that requires a well-organized postural stability to endure the crucial declined somatosensory input of the other leg. During standing on non-dominant lower extremity, individuals are more prone to increase sway in closed eyes conditions. Therefore, Achilles’ heel of balance system during standing on non-dominant leg was the absence of visual input ⁴⁰. This also accords with our earlier observations in this study, which showed that dominant leg standing balance was challenged when participants closed their eyes. During the course of this study the hardest situation of standing on dominant leg was eyes-closed conditions; as a result, these identified trials are recommended to be firmly tested to prevent an unsafe Achilles’ heel of equilibrium. It is accordingly recommended and would be better for these situations to be encompassed in screening, assessment, evaluation and future early fall preventive programs.

It is worth mentioning that the elderly participants in Zeynalzadeh et al.’s study were at the early stage of their senescence, meanwhile Era has reported that postural stability and control may encounter deficits especially when the elderly subjects are 75 to 80 years old and their weak postural control may lead to subsequent balance issues ³³. There are several possible explanations for this issue. A possible explanation for these may be implied in Maylor assumption. Maylor believes that balance performance and stability would be influenced and decreased in the process of aging as well ³⁸. Another possible explanation in the same fashion, is Bohannon’s reports who has reviewed studies which had reported that aging would lead to reduction of one leg standing duration ²⁰. In addition, Lajoie reports that in comparison to fallers, healthy individuals have a slower sway ³⁴. Teasdale mentioned that in the case of reducing sensory inputs, maintaining balance would be harder in elderly subjects ²⁷.

Ruffieux declared that postural balance needs cognitive processing to some extent ³⁷. As Ruffieux revealed and highlighted, this issue and these effects are yet to be investigated. So we aimed to find evidence in older adults during dual task performance. In the present study, under dual task conditions, participants showed tighter postural control to survive the challenge of one leg standing while confronting secondary imposed attention demanding task which was characterized by reduced sway (although not statistically significant).

The outcomes of this study are consistent with the results of past studies in which sway can be reduced by performimg cognitive tasks, concluding that postural sway may be associated with cognitive operation ³⁰. Soangra also believed that there is an interaction between postural task and the cognitive one in which exploring the interaction can help to prevent falling in healthy individuals with fall history. The result of Soangra’s study specifies that dual task does not necessarily pose the risk of fall in healthy individuals and their new adaptive strategy can be called “Cautious Mode”, which is not essentially destabilizing ⁶. Our findings is consistent with that of Bonnet (2016) who described that during standing even in motionless conditions there is a constant sway, which would be different under dual task conditions (like a cognitive performance). Bonnet explained that in the particular setting of active visual tasks, young adults showed less sway ⁴¹. As Maylor described, balance may be influenced by cognitive tasks in different ages and task types ³⁸. According to the Andersson’s study, changes of postural response were probable to be an adaptation strategy for lessening attentional demand and declining the risk of fall within restricted accessible attentional resources ³⁰. There are similarities between the attitudes expressed by COP variables in this study and those described by Swan, who mentioned dual tasks (spatial or non-spatial memory tasks) can progress older adults balance during the hardest postural circumstances ²⁸. Moreover, Pellecchia declared that attentional burden of cognitive task can influence balance ²⁹. Meanwhile, Brauer reported that postural retrieval was attention demanding, but the capability of healthy elderly subjects to pull through was not impacted by synchronized task burden ¹⁰. On the contrary, Dai has found that imposed stimulus like cognitive task may decline postural performance ¹².

One of the issues that emerges from these findings is the role of dominant leg. These findings may help us to understand the importance of visual input contribution to balance during one leg standing. While preliminary, this finding, suggests that routine assessment of healthy elderly balance on one leg should not be ignored. This study suggests that a protocol rich in sensory manipulation may help to detect weaknesses and prevent fall. These findings raise intriguing questions regarding the nature and extent of performing dual task. This combination of findings provides some support for the conceptual premise that visual input has one of the most vital capacities contributing to balance. Eliminating visual input would help to evaluate vestibular and somatosensory inputs contributions, since it brings in more vestibular and somatosensory inputs. The proper screening and early evaluation is a promising area in enabling, empowering and preventive care of people with apparently healthy aging. It also create a field to successfully test and identify older adults who are at risk of falling. The findings make an important contribution to the field of enhancing early intervention and global screening of general elderly balance. Active and community-living older adults were studied in this study, so those living in nursing homes or having inactive life style were missed. Accordingly, the latter population is also needed to be considered along with older healthy individuals in order for generalization of findings. According to this limitation, these findings cannot necessarily be extrapolated to different patients. Therefore, future research can focus more on balance-impaired elderly population.

CONCLUSIONS

Simulating real life conditions of dark environment, eliminating visual input, performing a secondary task and manipulating contribution of sensory system can possibly be provided if the protocol format of this study with four previously described conditions is applied. Therefore, the mentioned test conditions in this study can be suggested as the preferred test protocol and balance task assignment for healthy elderly population, helping identify the indivituals with potential risk of falling. It is imperative to measure objective postural assessments and it should be incorporated into comprehensive evaluation to assess different domains of balance function. The most paramount message of the present study is that visual input has a critical role in disturbing balance of even healthy elderly population during standing on dominant leg. Therefore, it is critical to modulate automatic and postural responses in order to gain some degree of adaptation. Vision as a corner stone must be monitored, so that its absence does not turn into Achilles’ heel of balance performance and its usage in balance assessment is seriously suggested, using “Area” and “Velocity” parameters of COP by Forceplate technology. This may be of value in development of public balance empowering and health enhancement agendas.

Figures and tables

Figure 1.Mean “Area” during each specific condition.

Figure 2.Mean “Velocity” during each specific condition.

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