This study progresses our previous work [3], providing comprehensive examination of free-living gait and turning characteristics concurrently measured by a single IMU in those with chronic mTBI and healthy controls. Our results demonstrate that free-living turning is more sensitive than free-living gait in differentiating chronic mTBI from controls, with turn duration being the most sensitive outcome. Free-living assessment in mTBI is still an emerging research area, but these results coupled with those from other neurological conditions (e.g. Parkinson's disease) suggest that impaired turning occurs with neurological dysfunction [50]. Assessment of free-living mobility in chronic mTBI may allow for improved diagnostics and monitoring of recovery, as well as development of individualised and targeted rehabilitation.
Free-living turning is impaired in chronic mTBI
Previous research has shown that physical impairments can be particularly prevalent in mTBI, due to the disruption in cognitive processing required to perform mobility such as turning and walking [5,7,8]. In agreement with our hypothesis, our results show that free-living turning was impaired in chronic mTBI compared to controls. Altered free-living turning in chronic mTBI expands upon previous results that have highlighted the importance of measuring turns in this cohort [3,51]. Turning is particularly relevant to mTBI due to the requirement of combined cognitive, sensory and motor processing that can be impacted by an mTBI [23,40,42]. Therefore, monitoring of turning can provide key metrics to monitor mTBI impairments, which is achievable in free living assessment as humans perform over 1000 turns per day [29,30].
Our results are consistent with our previous study in a smaller number of this mTBI cohort, which showed that free-living turn angle, duration, velocity and variability are impaired in chronic mTBI compared to healthy controls [3]. Greater turn duration, velocity, variability and angle may reflect reduced dynamic balance control in chronic mTBI that may impact confidence in turning [51]. For example, those with chronic mTBI may take more time to turn, and have more variability whilst avoiding smaller/quicker turns which may induce unwanted symptoms [51]. In contrast to our previous study, which incorporated in a smaller sample of this chronic mTBI cohort, there were no significant differences in the number of turns exhibited in those with chronic mTBI [3]. This suggests that other turning characteristics are better at distinguishing mTBI from healthy controls. As such those with chronic mTBI may be able to complete a comparable number of turns compared to controls, but the deficits from mTBI impact the quality of turning.
Our findings do corroborate with our previous free-living [3] and laboratory-based studies [51] that have shown peak turning velocity and average turning velocity to be impaired (lower) in the chronic mTBI group. Previous research from laboratory-based assessment has found that individuals with chronic mTBI may reduce their turning velocity due to impaired head stabilisation and mTBI symptoms [51]. Head stabilisation or coordination has yet to be explored fully in free-living environments, but it is reasonable that this coupling or coordination is also reduced in free-living environments and may explain the similarities seen in reduced peak turning velocity in people with chronic mTBI. Further work is required to examine and understand the origin of free-living turning deficits.
Free living gait characteristics are not impaired in chronic mTBI
Lack of significant differences and low effect sizes in gait characteristics between chromic mTBI and health controls may be related to the considerable chronicity (median 1.2 years post injury) of this mTBI cohort. Meaning this cohort of chronic mTBI may have developed compensation strategies over-time to replicate ‘normal’ gait patterns during walking in their daily life, whereas turning may require more cognitive or sensory processing, which may be a complex task that is difficult to compensate for and therefore turning reveals subtle mobility deficits [23,33,53]. As such, we would expect if we tested these participants in the laboratory under complex conditions (e.g. dual-task, obstacle walking, turns course etc.), we might detect more deficits in gait between chronic mTBI and controls. More longitudinal analysis of chronic mTBI patients during different stages of recovery (acute to chronic) would be beneficial to monitor impairments and recovery in free-living mobility characteristics.
Currently, there is no definitive way of objectively understanding the reasons for lack of differences in free-living gait between our chronic mTBI and healthy control cohorts, as there are many unknown factors that affect free-living assessments. For example, not knowing the environments people were regularly walking in, the surfaces they walked on, or the types of terrain encountered [54]. Equally, it is not possible to quantify the usual free-living mobility habits of the participants or if this cohort display any compensatory behaviour strategies (e.g. refraining from talking or performing other tasks whilst walking). The introduction of egocentric video recordings of free-living mobility may allow for better understanding and a robust reference [55]. If used in conjunction with objective free-living IMU assessment, video assessment could yield even greater understanding of free-living gait performance and any compensatory behaviour mTBI patients display within an environment.
Strengths and limitations
The primary strength of this study was the use of a single IMU to objectively measure free-living gait and turning in chronic mTBI patients and controls, as the use of a single device and assessment within usual daily life means that subjects had low research burden. However, the outcome measures presented are primarily research-orientated, requiring a great deal of time-consuming post-processing and checking, which is based on prior experience of inertial data [57,58]. Therefore, there needs to be refinement and deployment of software that clinicians and patients can easily navigate, which would allow more widespread uptake and use by health professionals [58]. Participants were assessed for ~7 days using a single IMU attached to a waist belt. However variation in the exact length of time participants wore wearables (minimum three days) could introduce differences and therefore not reflect true habitual free-living mobility as used in other studies [50,59]. Using multiple IMUs may provide more detailed spatial and temporal data for turning, balance and gait as used in previous studies [23], but this carries different limitations; such as longer data download, processing complexity and increased wearer burden, limiting the practical or clinical application. This trade-off should be considered in future studies as a potential improvement to the assessment protocol. [60,61].
There were some additional limitations to this study. Firstly, a more detailed demographic profile could be reported in future studies to derive further inferences about the free-living mobility results or underlying physiological mechanisms for persistent symptom and mobility deficits [23]. For example, the symptom questionnaires were limited to NSI that were only completed by the mTBI cohort, which limited any useful comparisons and inference on the relationship between groups [3]. Secondly, balance problems in the chronic mTBI were self-reported with no baseline or robust analysis done to quantify the magnitude of impairment [3], with the many factors such as the previous history of mTBI and evidence of abnormal neuroimaging omitted [4,56]. Thirdly, the differences in this mTBI cohort's chronicity are likely to limit the direct comparison with other studies. Our study's cohort was chronic with a median post-injury time greater than 1-year, which compared to other studies examining people post-mTBI is a long time since injury [23,51].