The interacting effect of cognitive and motor task demands on performance of gait, balance and cognition in young adults
Highlights
► Effects of DT walking at constant speed on gait variables, stability and cognition. ► Average temporal gait variables or COP excursion were not affected by DT walking. ► Variation of temporal gait variables increased during DT walking. ► Trunk motion was found to decrease during DT walking. ► Cognitive performance decreased during DT walking.
Introduction
Successful aging has become one of the most important aspects of health care in the 21st century. As people live longer risks of cumulative illness, chronic disability increase [1], [2]. Mobility limitations and cognitive impairments, both common with aging, reduce levels of physical and mental activity, are prognostic of future adverse health events, and are associated with an increased fall risk [2]. Importantly, the link between cognitive impairment, mobility limitations and the tendency to falls is recognized in the literature [3].
Maintaining stability during walking through the environment is a complex, multi-dimensional process requiring higher level motor control, and cognitive flexibility to address balance threats, while attending to environmental demands and concurrent cognitive tasks [2]. A key factor in locomotor control is executive cognitive functioning and deficits are associated with increased risk of falling [3], [4]. Various dual task (DT) studies have affirmed that difficulty in assigning attention to each task simultaneously may contribute significantly to increased fall risks. Poor DT performance in either the motor or cognitive task could be caused by altered prioritization between the two tasks [5]. The most common and consistent finding of DT studies has been the reduction of gait speed [3], likely as a strategy for concurrent task processing or to avoid stability threat. Reduced speed is commonly observed in elderly, and when negotiating obstacles, irregular or unpredictable terrain [6].
Dual-task studies have utilized cognitive tasks, like animal enumeration or number subtraction that are typically only assessed qualitatively, do not involve the visuomotor system and are limited in recruitment of individual brain areas. Visual–spatial processing of object locations/motions and their spatial relations with respect to body and space are key aspects of balance and locomotor skills, and evidence supports visual–spatial processing as an important aspect of cognition to explore in mobility decline [7], [8].
Virtual environments, viewed during treadmill walking, have been used as an ecological approach to rehabilitation [9]. Computerized cognitive tasks and games have received interest from researchers and clinicians, both as a model for learning a broad range of cognitive tasks and as a means to examine training and transfer of skills to daily life activities [10], [11], [12]. A treadmill rehabilitation platform (TRP) was designed around a treadmill as it is an excellent choice for conducting gait training with dual-tasks. It can incorporate walking skills while interacting with computer-generated cognitive activities viewed on a standard LCD display [9]. DT treadmill walking has important advantages versus over ground walking as gait variables are significantly influenced by walking speed [13], [14] and reduced gait speed is a highly consistent strategy used during dual-task over-ground walking [3]. It is a convenient method to determine steady-state walking speed. It also allows gathering hundreds of consecutive steps in a few minutes. Data from 5–10 strides (i.e. in gait laboratories or during repeated walks over short, instrumented walkways) may reliably measure gait speed, but is not sufficient for measures of gait variability or periodicity, particularly during dual task walking and for older adults with mobility limitations [15], [16].
The purpose of this study was to further explore the interplay between cognitive and walking demands on task performance. Since previous studies have shown that gait speed is an important factor affecting gait parameters, the treadmill speed is held constant to prevent a strategy of slowing walking speed. The first objective was to evaluate the effect of walking speed on temporal gait parameters and measures of walking stability, amplitude and variation of center of foot pressure (COP) displacements and trunk motion. The objective was to examine whether divided attention during walking at a constant speed would decrease locomotor rhythm, stability, and cognitive performance. This study addresses three hypotheses:
- (1)
Walking speed has a significant effect on temporal gait variables, and measures representing walking stability.
- (2)
Stability, locomotor, and cognitive performance will significantly decline from single task to DT conditions during constant speed.
- (3)
Cognitive performance will decline with increasing treadmill speed.
Section snippets
Methods
Twenty healthy young adults aged 20–30 years (mean age 26.3 ± 3.2 years) participated. Participants were excluded if they had past neurological impairment, musculoskeletal disorder or were taking medications that may have influenced their walking.
Instrumentation and data recording
Fig. 1 illustrates the experimental set-up. Participants were positioned on the treadmill 100 cm from the 30-inch monitor connected to a computer running the cognitive game. Vertical foot contact pressures were recorded from each foot using in-shoe pressure insoles. (Vista Medical Ltd, WPG. MB). The pressure insoles each consist of an array of 128 piezo-resistive sensors, calibrated to 300 mm Hg (12-bit). Pressure signals from left and right insoles were recorded at 35 Hz. The 3D Track STAR
Cognitive game task
Studies have used computer-based games to probe and evaluate cognitive function [11]. The Useful Field of View (UFOV) is a computer-based test that requires the ability to select relevant information and ignore irrelevant information (cognitive inhibition) [19]. Studies have found that older adults with slower cognitive speed of processing, as measured by the UFOV test, experienced the greatest mobility loss [20]. A modified version of the UFOV has been designed to evaluate visual–spatial
Protocol
Participants played the computer game using a standard optical mouse for 2 min in sitting to familiarize themselves with the cognitive task. The viewing height of the display during sitting and walking was maintained by placing an adjustable stool on the treadmill. A rest period of 2–3 min was given between test conditions. Participants walked on a level treadmill for 10 min at 0.7 m/s for treadmill acclimation. During testing, participants walked for 2 min at two treadmill speeds; 0.7 m/s (lower
Data analysis
Custom built scripts in MATLAB version 7.1 (The Math Works, Natick, MA) processed the pressure data of each insole array into footfall patterns. Time indices were computed for pressure onset and offset, stance and swing phases for each right and left step, and double support times. The average and coefficient of variation (COV) of stance time (ST), swing time (SW), and double support time (DS) were computed for each walk trial (45 steps per leg). These gait variables have been identified based
Statistical analysis
A two-way repeated measures ANOVA was used to determine the effects of treadmill speed and cognitive load (single vs. DT conditions) on temporal gait variables, COP and trunk excursion measures, and cognitive performance measures. The significance level was set at alpha level of 0.5.
Results
Group means and standard error of means (SEM) for average and COV of ST, SW, and DS are presented in Fig. 3. There was no significant difference in gait variables (average or COV) between left and right steps and therefore only results of analysis of right steps is presented in Table A1 (Appendix A). Average and COV of ST, SW and DS significantly decreased as a function of walking speed (p < 0.01). There was no significant effect of cognitive load for walk only versus DT walking on average ST,
Discussion
Treadmill speed had a significant effect on temporal gait variables (average and COV) in keeping with previous studies. The present results are consistent with Jordan et al. [13] and Kang and Dingwell [27] who observed a decrease in gait variability with increased walking speed. Measures of variability provide a perspective on the consistency of locomotor rhythm, and are often reported to represent walking stability. This view is supported by the present findings wherein the magnitude and
Funding
None.
Conflict of interest
There is no conflict of interest.
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