This is the first study to investigate if specific step parameters during the TUG test can discriminate between groups with different cognitive ability. The results varied depending on group comparison, TUG condition and step parameter. Nevertheless, step length was the step parameter that most consistently discriminated between the different groups and gait conditions.
Considering the step length/height parameter, both the TUG and TUGdt-MB conditions significantly discriminated between the groups, with the highest sORs occurring during the latter condition. Conversely, TUGdt-NA was the only condition that significantly discriminated between the MCI and the SCI groups, whereas all TUG conditions discriminated between the dementia and MCI groups (with the highest sOR for the TUG condition). For step duration, only the TUG condition significantly discriminated between the SCI and control groups, whereas both TUGdt conditions significantly discriminated between the dementia and MCI groups, with similar sORs. The only groups that DS duration significantly discriminated between were the dementia and MCI groups, and only during the TUGdt conditions, where TUGdt-NA had the highest sOR. Since our results suggested that step length was the parameter that showed the highest potential to discriminate between adjacent groups, ROC curves were conducted for the conditions that showed the highest sORs (i.e. TUGst and TUGdt-MB for the comparison of SCI and control groups). Since the results showed acceptable predictive ability (C ≥ 0.7) for both these conditions, the optimal cut-off value (using the established step length to body-height ratio) was then calculated for TUGdt-MB, as it had the highest sOR of the two conditions. A step length of less than 32.9% of the body height while conducting the TUGdt-MB was the optimal cut-off value for indicating that an individual experienced SCI.
With some variation, there was an overall trend that groups with more severe cognitive impairment walked with shorter steps both during the TUG condition and the two TUGdt conditions. These results are in accordance with previous studies where shorter stride/step length has been found to occur in groups with dementia compared to MCI and/or controls [10, 38] as well as between people with MCI and controls [39]. However, those studies were conducted while participants performed straight, overground walking, primarily in movement laboratory settings. The finding that the group with SCI walked with shorter steps than controls is a particularly novel and potentially important finding, rarely identified in previous studies [40]. This is of particular interest as SCI is defined as “self-reported impairment that cannot be identified during standard cognitive assessment”. Bearing in mind the importance of early detection of cognitive impairment, this result may highlight the importance of investigating step length during the TUG test during both single and dual-task conditions. Therefore, the optimal cut-off calculated in this study may be used to obtain an absolute value when assessing patients in clinical settings. Nevertheless, this is a novel finding that needs to be confirmed by future studies.
This study was designed to be conducted in the clinical settings of two different hospitals, where individuals undergoing memory assessment were recruited. This was done to maximize the study´s ecological validity as well as to facilitate integrating this assessment into a standard cognitive assessment battery, should the results motivate this. Given that it has previously been highlighted that deviant gait precedes cognitive impairment, and that such deviances may be even more evident while conducting motor-cognitive dual-tasking, two different types of cognitive task were integrated into the protocol. The first task, TUGdt-NA, is an established dual-task [41] inspired by the verbal fluency test. The other task, TUGdt-MB, was first presented in a pilot study from our research group [21]. This task was developed to be a more feasible version of the common task counting backwards by 7s. Indeed, the importance of using a cognitive task of adequate difficulty (i.e. not too easy nor too difficult) has been emphasized in the developing field of motor-cognitive dual-tasking [42]. Since the aim of UDDGait is to pin-point individuals that already experience cognitive deficits, this task, developed to challenge cognitive inhibition, was considered of appropriate difficulty level while also being feasible to use during clinical assessment. Regardless of the step parameter considered, no TUG condition significantly discriminated between all adjacent groups. However, the only non-significant discrimination by step length for the TUGdt-MB condition was between the MCI and SCI groups. These findings may indicate that the TUGdt-MB task is preferable to TUGdt-NA for discriminating between groups with low levels of cognitive impairment, which might be argued to be of particular importance for early detection of cognitive decline. The interpretation of the potential advantage of TUGdt-MB is also supported by the findings in a previous study by our research group, where this TUG-condition had the highest OR when using the parameter number of months correctly recited per 10 seconds for discriminating between SCI and controls [23].
This study has several limitations. Since participants only conducted one trial per gait condition, the total number of steps included to calculate parameter mean values was limited which may be a reason for the high variability found within the different parameters. This is one reason why previous studies using an instrumented TUG have often extended the distance [43], which in turn require more spacious assessment facilities. Another potential limitation is that body height rather than leg length was recorded since this information could be derived from patient charts. Although step length is proportional both to leg length and body height [44], the lack of a direct measure of leg length may interfere with the specificity of these results. On the other hand, this project was designed to facilitate the implementation of relevant findings into clinical practice. Therefore, the assessment procedures were conducted similar to how patients are assessed in healthcare settings (i.e. conducting each test once, not least due to time constraints). In addition, participants were older adults with varied cognitive and physical status, therefore using only one trial per TUG condition minimized fatigue in those participants with less physical or cognitive reserves. Indeed, clinical research has been criticized for commonly excluding potential participants with higher degrees of disability [45]. Another limitation of this study was the use of multiple analyses, which may result in significant results by chance. One way to reduce this possibility would have been to use the Bonferroni correction. However, the Bonferroni correction is highly conservative which can lead to a substantial risk of type 2 error [46]. Instead, these results should be interpreted with caution and confirmed by future research.