Functional parameters indicative of mild cognitive impairment: a systematic review using instrumented kinematic assessment

The global life expectancy is increasing in the last years. Consequently, morbidity, chronic individual diseases and the number of people affected by dementia are also increasing [1‐5]. Thus, while dementias affected around 46.8 million people worldwide in 2016 [5], it is expected that in 2050 there will be 115–135 million people suffering from dementia [6, 7]. There is an increase in the interest of mild cognitive impairment (MCI), defined as a clinical stage accounting for cognitive impairment that often precedes dementia [5, 8‐17], and whose prevalence in adults of ≥65 years old is 10–20%, increasing this prevalence with age [5, 8].

Accepted diagnosis criteria of MCI reported that patients with MCI were characterized by an objective impairment of cognition that is often not severe enough to interfere with activities of daily living (ADL), instrumental activities of daily living (IADL) or in social or occupational functioning [5, 8, 10‐14, 17‐21]. In the same way, Petersen [11] determined that patients with MCI presented very mild degrees of functional impairment that is difficult to distinguish from the functional problems of cognitively healthy individuals of the same age. However, patients with MCI may have problems in functional tasks [5] and it has been reported that these patients present the alteration of functional parameters, such as mobility, muscle strength, balance, gait dysfunction, or increased risk of falls [8, 22‐26]. Slower gait speed has also been suggested as the mainly altered parameter in older populations [23‐25, 27‐32] which may be a marker for the preclinical stages of dementia [23, 30‐33]. Thus, Doi et al. [34], Eggermont et al. [35] and Deshpande et al. [36] reported that slower gait speed could be indicative of MCI. Veronese et al. [30] showed an association between decreased gait speed and low performance in the Short Physical Performance Battery (SPPB) and cognitive decline. Other functional tests, such as Timed Up Go (TUG), Hand Grip Strength Test (HGST), Sit to Stand Test (STS), or Walking Speed ​​Test (WST), have also been used to demonstrate the association between the performance on functional tests and MCI [22, 30, 37, 38].

However, Mirelman et al. [39] reported that patients with MCI could have functional alterations only identifiable through a kinematic analysis conducted in their case with an inertial sensor. In this way, Bahureksa et al. [40] revealed that kinematic gait parameters such as velocity, stride length, and stride time best discriminated patients with MCI from cognitively healthy individuals under single task (ST) conditions and, above all, under dual task (DT) conditions. Balance parameters such as anterior-posterior and medio-lateral sway position also were identified as significant discriminators [40]. Kinematic measurements are frequently used by physicians and researchers to quantify normal and pathological movements and could allow to identify altered objective functional parameters in patients with MCI [41]. The identification of changes in functional objective parameters could be relevant for targeting specific interventions aiming to prevent further functional decline or to improve the functionality of patients with MCI. Currently, no drug has been shown to be effective for MCI [8, 17, 18, 42]. However, it has been reported that the combination of aerobic exercise, balance training, cognitive training, the Mediterranean diet and social commitment could reduce the risk of further cognitive impaiment and may improve cognition, mobility, balance and quality of life in patients with MCI [8, 17, 18, 43, 44]. Considering this, the main objectives of this systematic review were (1) to examine if functional kinematic parameters may predict a future risk of MCI; (2) to compare these functional objective parameters in patients with MCI and a control group; (3) to assess longitudinal changes in these parameters after different physical activity interventions. The secondary objectives were (1) to assess the risk of bias of the included studies using The Newcastle-Ottawa Quality Assessment Scale (NOS) and The Cochrane Collaboration’s tool; (2) to assess the level of evidence per outcome using the Grading of Recommendations Assessment, Development and Evaluation (GRADE).

This systematic review was carried out in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement [45]. The PRISMA checklist for this trial is available in supplementary appendix A. The systematic review protocol was registered at the International Prospective Register of Systematic Reviews (PROSPERO: CRD42019119180).

Slower gait speed in ST condition and, above all, in DT conditions and larger gait speed variability are the parameters that best discriminate patients with MCI from a control group. Slower gait speed and larger gait variability may also predict an incident MCI or could even help its early diagnosis. Some functional objective parameters such as gait speed, stride length, stride time, balance and the time to perform the TUG may be improved by aerobic exercises when aerobic exercises are performed alongside cognitive stimulation exercises or others physical exercises such as muscle strength training, postural balance retraining, or gait training. Although most of the cohort studies showed a low risk of bias, RCTs reported unclear risk of bias and GRADE criteria showed a low level of evidence per outcome, so further studies are required to confirm our findings.