Temporal characteristics of imagined and actual walking in frail older adults

  • Hideki Nakano
  • Shin Murata
  • Kayoko Shiraiwa
  • Hiroaki Iwase
  • Takayuki Kodama
Original Article
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Abstract

Background

Mental chronometry, commonly used to evaluate motor imagery ability, measures the imagined time required for movements. Previous studies investigating mental chronometry of walking have investigated healthy older adults. However, mental chronometry in frail older adults has not yet been clarified.

Aims

To investigate temporal characteristics of imagined and actual walking in frail older adults.

Methods

We investigated the time required for imagined and actual walking along three walkways of different widths [width(s): 50, 25, 15 cm × length: 5 m] in 29 frail older adults and 20 young adults. Imagined walking was measured with mental chronometry.

Results

We observed significantly longer imagined and actual walking times along walkways of 50, 25, and 15 cm width in frail older adults compared with young adults. Moreover, temporal differences (absolute error) between imagined and actual walking were significantly greater in frail older adults than in young adults along walkways with a width of 25 and 15 cm. Furthermore, we observed significant differences in temporal differences (constant error) between frail older adults and young adults for walkways with a width of 25 and 15 cm. Frail older adults tended to underestimate actual walking time in imagined walking trials.

Conclusions

Our results suggest that walkways of different widths may be a useful tool to evaluate age-related changes in imagined and actual walking in frail older adults.

Keywords

Frail older adult Walking Motor imagery Mental chronometry 

Introduction

Motor imagery involves mental simulation of movement without actual movement [1], and can effectively improve motor skill [2] and increase muscle strength [3]. It has also been widely applied in rehabilitation and sport [4, 5]. Motor imagery consistently recruits a large fronto–parietal network, and subcortical and cerebellar regions, known to play a role in actual motor execution [6]. Mental chronometry is commonly used to evaluate motor imagery ability [7]. For example, it has been reported that the mental practice of motor imagery is effective as a rehabilitation tool for stroke patients [8]. Moreover, mental chronometry is used as an evaluation index of motor imagery before and after such training [9]. Mental chronometry measures imagined time required for movement. Smaller differences between imagined and actual times suggest higher motor imagery ability [10]. Imagined and actual times for movement tend to be similar and both elicit activation of brain regions related to motor imagery [11].

Schott et al. [12, 13] reported greater temporal incongruence in older adults than in young adults, and increased incongruence as walkways become longer. Similarly, Personnier et al. [14] reported greater temporal incongruence in older than in younger adults, and increased incongruence with narrower walkways. Moreover, in a study that used tasks of differing complexity in real-life situations, it was reported that there was greater temporal incongruence in older than in younger adults, and it increases with task complexity [15]. Such studies suggest there is increased time incongruence between imagined and actual walking in older adults compared with young adults, and it is also affected by task difficulty.

Of course, older adults may be healthy and able to independently undertake activities of daily living (ADL), or frail if such abilities are decreasing [16]. As physical function decreases in frail older adults, mental chronometry, an index of motor imagery, may differ from that of healthy older adults. Previous studies [12, 13, 14, 15] investigating mental chronometry of walking have investigated healthy older adults able to independently undertake ADL, while mental chronometry in frail older adults has not yet been clarified. Therefore, we aimed to clarify temporal characteristics of imagined and actual walking in frail older adults.

Methods

We recruited 29 frail older adults [female, n = 14; male, n = 15; mean age ± standard deviation (SD): 78.9 ± 6.7 years] from Japanese long-term care insurance (LTCI) services [17], and 20 young adults [female n = 10, male n = 10; mean age: 22.2 ± 9.2 years]. Older adults using LTCI services have physical or mental impairment and need assistance to perform ADL [18]. Participants with Mini-Mental State Examination (MMSE) scores below 24, chronic orthopedic, neurological, or psychiatric diseases that might influence the results, or inability to walk independently were excluded.

The study was conducted according to the principles of the Declaration of Helsinki and was approved by the local institutional ethics committee (Kyoto Tachibana University). All participants provided informed written consent and were free to withdraw from the study at any time.

Participants measured the time required for imagined and actual walking along three walkways of different widths [width(s): 50, 25, 15 cm × length: 5 m] [12]. First, participants stood in front of one type of walkway and imagined walking along it, with speed of imagined walking set as the normal speed. Participants measured imagined walking with mental chronometry using a stopwatch. Subsequently, participants imagined walking along the other two types of walkways. Walkways were presented in a random order. Next, participants stood in front of one type of walkway and actually walked along it. The speed of actual walking was set as the normal speed, and the tester measured it with a stopwatch. The participant then walked along the remaining two types of walkways, with the walkways presented in a random order.

We calculated temporal differences (absolute and constant error) between imagined and actual walking with the following formulae: Absolute error = |Actual time − Imagination time|; Constant error = Actual time − Imagination time [12]. Constant error was used to examine the bias between actual and imagined times. This score reflects a participant’s bias in performance. However, negative and positive values can cancel each other out when averaging. Therefore, it is important to report an error term that is not affected by scores of opposing signs. In this context, absolute error provided a measure that is independent of directional bias and reflects overall accuracy [12].

Imagined and actual walking times were analyzed with a 2 (group: frail old, young) × 2 (condition: imagined, actual) × 3 (width: 50, 25, 15 cm) ANOVA. We assessed which group, condition, or width showed significant differences with post hoc Bonferroni testing. Absolute and constant error were analyzed with a 2 (group: frail old, young) × 3 (width: 50, 25, 15 cm) ANOVA and post hoc Bonferroni testing to assess which group or width showed significant differences. Statistical analyses were performed with SPSS ver. 23.0 (IBM, Chicago, IL, USA), with a significance level of p < 0.05.

Results

In this study, there were no participants with MMSE scores below 24, or chronic orthopedic, neurological, or psychiatric diseases that might influence the results. Furthermore, those with inability to walk independently were excluded. However, the frail older adults who participated in this study needed assistance to perform ADL because of declining physical function with age.

Three-way ANOVA showed a significant interaction of group × condition × width (F = 12.83, p < 0.01). Post hoc Bonferroni comparisons revealed that imagined and actual walking times along all walkways were significantly greater in frail older adults compared with young adults (p < 0.01). Moreover, there significant differences between imagined walking time for walkways of 50 and 25 cm width (p < 0.05), and a significant difference between actual walking time for walkways of 50 and 15 cm width (p < 0.01), and walkways of 25 and 15 cm width (p < 0.05) in frail older adults. Furthermore, we observed significant differences between imagined and actual walking times for walkways of 25 and 15 cm width in frail older adults (both p < 0.05). In contrast, no significant differences between imagined and actual walking times were observed in young adults (all p > 0.05) (Fig. 1).

Fig. 1

Comparison of imagined (IMA) and executed (EXE) times for walking in frail older and young adults. *p < 0.05, **p < 0.01

Two-way ANOVA for absolute error showed a significant interaction of group × width (F = 12.83, p < 0.01). Post hoc Bonferroni comparisons revealed that absolute error of frail older adults was significantly greater than that of young adults for 25 (p < 0.05) and 15 cm (p < 0.01) wide walkways (Fig. 2). Two-way ANOVA for constant error showed a significant interaction of group × width (F = 16.88, p < 0.01). Post hoc Bonferroni comparisons suggested significant differences in constant error between frail older adults and young adults for walkways with a width of 25 (p < 0.05) and 15 cm (p < 0.01) (Fig. 3).

Fig. 2

Comparison of absolute error in frail older and young adults. Absolute error reflects the absolute value of the difference between the actual and imagined times. This score provides a measure that is independent of directional bias and reflects overall accuracy. *p < 0.05, **p < 0.01

Fig. 3

Comparison of constant error in frail older and young adults. Constant error reflects the constant value of the difference between the actual and imagined times. This score reflects the bias between both actual and imagined times. *p < 0.05, **p < 0.01

Discussion

Our results suggest that imagined and actual walking times in frail older adults are significantly greater for than in young adults. Moreover, temporal differences (absolute error) in frail older adults were significantly greater than in young adults for walkways of 25 and 15 cm width, which is consistent with previous studies in healthy older adults [12, 13, 14, 15].

Previous studies reported that imagined and actual walking times and their temporal differences (absolute error) are significantly greater in older than in younger adults where the length [12, 13] and width [14] of walkways, or the environment [15] are altered. Deterioration of working memory function in older adults may affect motor imagery ability [13]. Here, we included frail older adults, in whom physical frailty may be associated with deterioration of working memory function [19]. Therefore, we hypothesized that imagined and actual walking times and their temporal differences (absolute error) would increase with narrower walkways in frail older adults.

We also observed significant differences in temporal differences (constant error) of imagined and actual walking times between frail older adults and young adults for 25- and 15-cm-wide walkways. Young adults had values close to zero or negative (overestimation of actual walking time in imagined walking trials), whereas frail older adults showed positive values (underestimation of actual walking time in imagined walking trials). This result differs from that of a previous study of healthy older adults, in which participants overestimated actual walking time during imagined walking trials [14]. In contrast, Sakurai et al. [20] reported that older adults with fear of falling underestimate actual walking time during imagined walking trials. This may be because motor imagery ability is affected by activity avoidance/inactive lifestyle resulting in/from fear of falling [20]. Our participants were frail older adults whose ability to perform ADL was declining. In older adults, declining ability to perform ADL is associated with fear of falling [21, 22]. Therefore, we suggest that frail older adults underestimated actual walking time in imagined walking trials, leading to significant differences between frail older adults and young adults in the temporal differences (constant error) between imagined and actual walking times.

Mental chronometry is a widely applied tool to evaluate motor imagery abilities in older adults [12, 13, 14, 15, 20], patients with stroke [10, 23], and patients with Parkinson’s disease [24, 25]. Our results suggest the methods we used have broad clinical application to evaluate motor imagery ability related to walking in frail older adults, judging the effectiveness of training and preventing falls.

Our study is subject to some limitations. First, we investigated frail older adults and young adults, but not healthy older adults. Temporal characteristics of imagined and actual walking should be investigated in frail older adults compared with healthy older adults. Second, we did not fully examine motor and cognitive functions of frail older adults. The relationship between motor and cognitive functions and temporal characteristics of imagined and actual walking in frail older adults should be addressed in future research.

In conclusion, we investigated temporal characteristics of imagined and actual walking in frail older adults. We observed increased temporal incongruence between imagined and actual walking in frail older adults with narrower walkways and significantly greater imagined and actual walking times along all walkways in frail older adults than in young adults. Finally, temporal differences (absolute and constant error) between imagined and actual walking of frail older adults were significantly greater than those of young adults for 25- and 15-cm-wide walkways. Our study suggests that walkways of differing widths may be useful to evaluate age-related changes in imagined and actual walking of frail older adults.

Notes

Acknowledgements

We would like to thank all volunteers who participated in this study.

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.

Ethical approval

All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards.

Informed consent

Informed consent was obtained from all individual participants included in the study.

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Copyright information

© Springer International Publishing AG, part of Springer Nature 2018

Authors and Affiliations

  • Hideki Nakano
    • 1
  • Shin Murata
    • 1
  • Kayoko Shiraiwa
    • 1
  • Hiroaki Iwase
    • 1
  • Takayuki Kodama
    • 1
  1. 1.Department of Physical Therapy, Faculty of Health ScienceKyoto Tachibana UniversityKyotoJapan

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