Research Article: Body position and motor imagery strategy effects on imagining gait in healthy adults: Results from a cross-sectional study

Date Published: March 15, 2018

Publisher: Public Library of Science

Author(s): Olivier Beauchet, Cyrille P. Launay, Harmehr Sekhon, Jennifer Gautier, Julia Chabot, Elise J. Levinoff, Gilles Allali, Yih-Kuen Jan.

http://doi.org/10.1371/journal.pone.0191513

Abstract

Assessment of changes in higher levels of gait control with aging is important to better understand age-related gait instability, with the perspective to improve the screening of individuals at risk for falls. The comparison between actual Timed Up and Go test (aTUG) and its imagined version (iTUG) is a simple clinical way to assess age-related changes in gait control. The modulations of iTUG performances by body positions and motor imagery (MI) strategies with normal aging have not been evaluated yet. This study aims 1) to compare the aTUG time with the iTUG time under different body positions (i.e., sitting, standing or supine) in healthy young and middle age, and older adults, and 2) to examine the associations of body positions and MI strategies (i.e., egocentric versus allocentric) with the time needed to complete the iTUG and the delta TUG time (i.e., relative difference between aTUG and iTUG) while taking into consideration clinical characteristics of participants.

A total of 60 healthy individuals (30 young and middle age participants 26.6±7.4 years, and 30 old participants 75.0±4.4 years) were recruited in this cross-sectional study. The iTUG was performed while sitting, standing and in supine position. Times of the aTUG, the iTUG under the three body positions, the TUG delta time and the strategies of MI (i.e., ego representation, defined as representation of the location of objects in space relative to the body axes of the self, versus allocentric representation defined as encoding information about body movement with respect to other object, the location of body being defined relative to the location of other objects) were used as outcomes. Age, sex, height, weight, number of drugs taken daily, level of physical activity and prevalence of closed eyes while performing iTUG were recorded.

The aTUG time is significantly greater than iTUG while sitting and standing (P<0.001), except when older participants are standing. A significant difference is reported between iTUG while sitting or standing and iTUG while supine (P≤0.002), higher time being reported in supine position. The multiple linear regressions confirm that the supine position is associated with significant increased iTUG (P≤0.04) and decreased TUG delta time (P≤0.010), regardless of the adjustment. Older participants use the allocentric MI while imagining TUG more frequently than young and middle age participants, regardless of body positions (P≤0.001). Allocentric MI strategy is associated with a significant decrease in iTUG (P = 0.037) only while adjusting for age. A significant increase of iTUG time is associated with age (P≤0.026). Supine position while imagining TUG represents a more accurate position of actual performance of TUG. Age has a limited effect on iTUG performance but is associated with a change in MI from ego to allocentric representation that decreases the iTUG performances, and thus increases the discrepancy with aTUG.

Partial Text

Motor imagery (MI) is defined as mentally simulating a given action without its execution [1]. MI is used to examine motor control in clinical studies and to identify the functional brain networks involved while performing a motor task in functional brain imaging studies [2–6]. For clinical use, MI performance is assessed using the mental chronometry approach in which the time course of the mental operation is compared to the time course of the performed action [1]. This approach has shown that MI retains many of the properties, in terms of temporal regularities, programming rules and biomechanical constraints, which are observed in the corresponding real action when it comes to execution [1–6]. MI is used as a technique to enhance motor learning and to improve rehabilitation in patients with neurological disorders like stroke [7,8]. More recently, the mental chronometry approach of MI has been used to assess gait impairment in older adults [7]. A better understanding of factors, which may influence MI performance, is required to develop an appropriate clinical test assessing gait impairment in an older population.

The mean age and the number of drugs taken daily are significantly different between groups; older adults took more drugs compared to younger adults (P<0.001, S1 Table). There is a trend for an increased BMI (P = 0.010), aTUG (P = 0.045) and iTUG (P = 0.075) times and a decreased height (P = 0.044) in older compared to young participants. Older participants use the egocentric strategy less frequently compared to their young and middle age counterparts, regardless of body positions (P≤0.001). Most of participants keep their eyes open while imagining TUG. They use the same MI strategy for all conditions of iTUG and there is no difference between groups (P = 0.739). As shown in S1 Fig, regardless of the category of participants (i.e., total population, young participants and old participants), aTUG time is significantly longer than iTUG while sitting and standing (P<0.001), except when older participants are standing. In this last case, there was only a trend (P = 0.011). There is no significant difference between aTUG and iTUG while supine, as well as, between iTUG while sitting and iTUG while standing, regardless of the group of participants (i.e., total population, young and middle age participants, older participants). A significant difference is reported between iTUG while sitting or standing and iTUG while supine (P≤0.002), higher time being reported in supine position. Comparisons between sitting and standing for delta TUG are non-significant, regardless of the group considered, whereas all other comparisons is significant (P≤0.001; S2 Fig). In addition, the two-way ANOVA with a repeated measure design showed that the body positions have a significant effect on iTUG (F = 21.1 with P<0.001) and TUG delta time (F = 25.3 with P<0.001). There was no interaction between the body positions and age (F = 0.2 with P = 0.830 for iTUG; F = 0.6 with P = 0.529 for delta TUG). As shown in S2 Table, multiple linear regressions show a significant increase of iTUG time with age (P≤0.026). Allocentric MI strategy is associated with significant decrease in iTUG (P = 0.037) while taking into consideration age, whereas there is a trend (P = 0.058) while taking into consideration age and body position. Supine position is associated with an increase in iTUG (P≤0.031), regardless the adjustment. Only supine position is associated with a significant decrease of delta TUG (≤0.010) (S3 Table). The findings show that iTUG performance is mainly influenced by body position. Supine position is associated with an increased iTUG time and a decreased delta TUG time. In addition, older participants more frequently use the allocentric MI strategy, which is a MI strategy associated with a decreased iTUG time. Furthermore, age is associated with an increased iTUG time. Thus, the best strategy and position, to minimize the discrepancy between aTUG and iTUG, which suggests appropriate gait control, are the egocentric strategy and the supine position, regardless of age. The results showed significant effects of body positions, MI strategies and age on iTUG performances, body position having the greatest impact. Supine position while imagining TUG represents a more accurate position of actual performance of TUG. Age has a limited effect on iTUG performance but is associated with a change in MI from ego to allocentric representation, which decreases the iTUG performances, and thus increases the discrepancy with aTUG.   Source: http://doi.org/10.1371/journal.pone.0191513