Full length articleAltered dynamic postural control during gait termination following concussion
Introduction
Impairments in postural control are a primary concussion symptom; thus, postural control testing is a recommended component of the multifaceted concussion assessment battery [1], [2]. Current concussion assessments include both clinical (Balance Error Scoring System (BESS)) and experimental (Sensory Organization Test (SOT)) protocols. The most commonly utilized clinical assessment tool, BESS, is limited by low interrater and intrarater reliability scores, test administration environment, and low sensitivity (0.34) acutely post-concussion [3], [4], [5], [6]. Despite its limitations, the BESS does have high content validity for identifying balance impairments following a concussion, and the modified version of the BESS, which is recommended by the 3rd edition of the Sport Concussion Assessment Tool, has demonstrated good reliability [7], [8], [9]. However, both the BESS and SOT are limited by substantial practice effects, potentially because these are novel tasks (e.g., standing barefoot on a foam surface with the eyes closed), and repeat administration has routinely identified improved performance [10], [11]. Further, the BESS and SOT are static assessments that rely on feedback mechanisms to maintain upright posture on an unstable surface and do not evaluate transitional, dynamic movements, which are likely more challenging to the postural control systems [12]. These limitations may explain the surprising finding that post-concussion static postural control often recovers prior to both symptom resolution and cognitive deficits [6]. Therefore, the utilization of common dynamic motor activities of daily living (ADL), which are unlikely to be subjected to a practice effect, may be more appropriate for identifying post-concussion impairments [13].
An acute post-concussion conservative gait strategy, consisting of reduced step velocity, step length, center of pressure (COP) and center of mass (COM) separation, as well as increased double support time and frontal plane COM sway, has been consistently identified [14], [15]. These deficits appear to persist for up to two months post-injury, suggesting impairments in dynamic postural control persist well beyond BESS recovery [16]. Gait is an innate, or non-novel, dynamic task, and the parameters are not generally susceptible to the practice effects in otherwise healthy young adults [17]. Gait performance is highly consistent in healthy college-aged recreational and student-athletes [18]. Specifically, changes in gait parameters (e.g., velocity, stride length) are most pronounced up to age 10, after which there are minimal changes in gait pattern [17]. Unlike quiet standing, unobstructed gait is less reliant on sensory feedback as both supraspinal planning (motor cortex and pyramidal tract) and central pattern generators are largely responsible for feedforward control [19], [20]. Further, transitional movements, such as initiating or terminating gait, are likely more challenging to dynamic postural control systems than gait, which likely increases the neurological resources required to safely complete the task [21].
Planned gait termination (GT) is a transitional motor task that encompasses the shift from cyclical gait to quiet standing and requires the central nervous system to anticipate, control, and slow the forward momentum of the body while maintaining the COM within the base of support (BOS) [22]. This transitional task is divided up into three phases: braking (S1), transitional (S2), and stabilization (S3). In fRMI studies, planned GT appears to be controlled supraspinally, with activation patterns identified within the right prefrontal area, specifically the right inferior frontal gyrus [19]. The planned GT task requires the participant be aware of the location or time to terminate gait and is comprised of a penultimate (second to last step before termination) and termination step [22]. Mechanically, planned GT requires two coupled braking mechanisms: (1) a reduction in the foot propulsive force during the penultimate step and (2) an increase in the braking force during the terminating step [22]. Thus, it is not surprising that GT has already identified both acute and lingering alterations in post-concussion propulsive and braking forces only; however, the COP trajectories have not been elucidated [23]. Further, individuals with compromised neurological systems (e.g., Parkinson’s disease, Cerebellar disease, moderate to severe traumatic brain injury) have noted planned GT deficits, including diminished COP displacements.
Planned GT is a stable, non-novel ADL task that challenges the postural control systems and that relies on active feedforward control [20]. Impaired postural control is a known consequence of concussion; however, most assessment protocols utilize novel static tasks that have not been associated with specific postural control mechanisms. Therefore, the purpose of this study was to evaluate planned GT performance between baseline and post-concussion individuals with comparison to healthy individuals. We hypothesize an interaction will be present wherein herein healthy control participants will demonstrate consistent task performance whereas the post-concussion participants will demonstrate an impairment during GT.
Section snippets
Participants
There were 38 participants in this study; 19 National Collegiate Athletic Association Division I student-athletes, from a single institution, diagnosed with a sports-related concussion and a control group consisting of 19 uninjured, physically active individuals from the same institution (Table 1). All concussions were identified by a certified athletic trainer and subsequently diagnosed by the team physician. The inclusion criteria for the concussion participants was a diagnosed concussion
Results
All participants completed the five trials without incident.
Discussion
This investigation utilized a mixed design analysis for the concussion participants, incorporating baseline data in the identification of post-concussion impairments in dynamic postural control. The main finding of this study was an altered COP displacement and velocity in the braking and transitional phases of planned GT, within the post-concussion group when compared to both their own baseline values and to matched controls. Specifically, a decreased COP displacement and velocity in the ML
Conflict of interest statement
There are no conflicts of interest associated with the present study.
Acknowledgements
This study was supported by the National Institute of Health/National Institute of Neurological Disorders and Stroke (1R15NS070744-01A1). The funding source had no role in the study design, data collection and interpretation, or decision to submit this manuscript for publication.
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