Our study found that among older adults aged 70–81 years, the general cycle is most associated with global cognitive function; when cognitive function is specified in domains, results showed better general cycle and initial contact phase related to better executive function, the general cycle phase was also related to the memory domain.
To the best of our knowledge, this is the first study to include most of the various gait parameters that almost consist of the whole gait phase when studying the association between gait and cognitive function. To date, various techniques have been used in gait analysis, including stopwatches, electronic walkways, body-worn sensors, electromyography, and 3D motion analysis [6, 14]. The technique used in this study was an easily wearable sensor that measured 3D gait. The 3D motion analysis is considered accurate and is used as the gold standard in gait analysis [18]. Moreover, we used conceptual models to summarize various parameters of gait factors. Previous studies have also used a conceptual model [13, 14, 19–21]; however, gait assessments in all those articles were performed using a walkway (GAITRite, CIR System Inc.). The nature of walkways determined that it can only assess general (velocity, width, cadence, and stride time) and temporal (time for swing, stance, single and double support, and turning) parameters, while those used in this study could additionally evaluate gait from spatial and clearance aspects, benefit from further factors of initial contact, propulsion, and mid-swing were output, which made the gait analysis more comprehensive. Hence, compared to most other studies using simple techniques, our results are more precise and show a complete relationship between gait and cognitive function.
After adjusting for several confounders, the results showed that only general cycle factors (predominantly cadence, speed, and stance time) were significantly associated with global cognitive function in all the participants. People with lower scores for the general cycle factor were inclined to have higher MoCA-J scores. Internal biomechanism can be referred to as the proved mechanism between gait speed and cognitive function. Some lesions of the brain, such as an increased proportion of the periventricular and subcortical white matter hyperintensities, atrophy of the medial temporal areas, hippocampal atrophy [22], or small gray matter volumes in the bilateral cortical and subcortical regions, based on magnetic resonance imaging [23] can slow the gait speed, while simultaneously impairing cognitive function. In addition, recent studies have started researching the biomechanism between other parameters and cognitive function; for example, higher cerebral amyloid-β deposition was shown to be associated with increased double support time [24]. Therefore, by involving more gait aspects, a more robust mechanism could be clear between gait and cognitive function.
With respect to newly invented factors of initial contact, propulsion, and mid-swing, no significance was found for global cognitive function. Although previous studies claimed that the contributor of stride length in the initial contact factor was related to cognitive function [25], their relationship was probably caused by the high correlation with gait speed. In addition, according to a study of brain dynamics while walking, electrocortical activity progressively decreases in the pre-swing phase and acceleration phase [26], which indicates that compared to the preparatory phases for the most important point of walking, the general cycle factor that includes characteristics of posture control (double support and foot-flat) is better associated with global cognitive function.
Further exploration of domain-specific cognitive function supported the strong association between executive function and gait [27, 28]. The term executive function refers to the higher-level cognitive skills we use to control and coordinate our other cognitive abilities and behaviors [29] traditionally, it is associated with the frontal lobes and related brain networks, in particular, the dorsolateral prefrontal cortex and cingulate cortex [30]. A previous study found that gait shared similar brain regions in which a great burden of subcortical white matter hyperintensities on magnetic resonance imaging is related to increased dual-task costs while walking [31], which could be the main reason for their high correlation. In addition, past studies have suggested that gait requires memory; shared anatomy can also be used to explain their robust relationship [32]. However, some individual gait parameters have a significant relationship with language and attention domain [33]. After being detained by the factor analysis, combined gait characteristics did not show any relationship with other domains except for executive function and memory domain. Therefore, enough evidence for an association between gait and the other two domains, orientation and visuospatial, in all the participants was not found [34].
Moreover, our results varied greatly in terms of sex. According to basic characteristics, men performed worse on both gait and cognitive assessment than women, which is proved by the previous studies that older women usually outperformed on the test of motor speed [35] and memory than men despite the same level of cognitive degeneration [36, 37]. Moreover, women showed a stronger relationship between gait and global cognitive function, and no significance relationship was observed in men. The cognitive benefit of physical activity may be greater in women than in men [38]; however, the effect and biological mechanism of sex on the relationship between gait and cognitive function remains unclear. These observations illustrate that sex difference is an important confounding factor in the study of gait and cognitive function among older adults, and it should be discussed in future work.
This study has both strengths and limitations. Although the advanced device and conceptual models used in this study makes it more comprehensive and precise, the following aspects still warrant some attention: first, this was a cross-sectional study, which meant that the causality between gait and cognitive function could not be determined. Second, during the process of measuring gait parameters, the first and last two cycles were not excluded given the short total distance, while the initiation and termination of gait are sometimes thought to be unstable and inaccurate [39]. As claimed by other studies, older adults need at least four gait cycles to reach steady-state walking speed [40]. Third, only the MoCA-J questionnaire was used in the cognitive assessment procedure, although the MoCA was identified as an applicable method for evaluating global and domain-specific cognition, a previous study claimed that the MoCA is not comparatively sensitive or specific for identifying attention or language impairments [41, 42]. To maintain the veracity of cognitive function, especially in the study of exploring different cognitive domains, extensive neuropsychological batteries should be added in the future research. Finally, the participants in our study were older than 70 years, and 70% of them had mild cognitive impairment (MCI) (MoCA < 26 is defined as MCI [43]). However, the prevalence of MCI among older adults usually ranges between 3% and 42% [44]. Atypical MCI prevalence may be associated with potential physical functional impairments and disease history of the participants, which we did not exclude before analysis, and this may make it difficult to generalize the results to a wider population.