Michael E. Cinelli

Recovery of static stability following a concussion

The purpose of this study was to use centre of pressure (COP) measurements to determine if static balance deficits had recovered when concussed athletes were cleared to return to play. Nine concussed varsity football players were matched with nine teammates who served as controls. Static balance in the anterior-posterior (A/P) and medial-lateral (M/L) directions was assessed during quiet stance with eyes open and eyes closed. Results showed that concussed football players displayed greater A/P COP displacements in the acute phase, which recovered by RTP; however, COP velocity remained elevated compared to controls even at RTP, particularly in the A/P direction. This balance control deficit in the A/P direction may suggest vestibular impairment, likely due to poor sensorimotor integration of the lateral vestibulospinal tract. The observed persistence of balance control deficits in concussed football players at RTP are usually undetected by traditional assessments because the current study used higher-order COP analysis. Future RTP balance measures may want to incorporate higher-order measures of balance.

Cortical hypoexcitability persists beyond the symptomatic phase of a concussion

Abstract Primary objective: The purpose of this research was to assess cortical excitability, voluntary activation of muscle and force sensation beyond the initial highly symptomatic period post-concussion (1–4 weeks post-injury). It was hypothesized that reduced excitability of the motor cortex may impair muscle activation and alter perceptions of force and effort. Research design: Eight concussed varsity football players were age- and position-matched with eight healthy teammates to control for training and body size. Healthy controls had not suffered a concussion in the previous 12 months. Methods and procedures: Paired-pulse transcranial magnetic stimulation was used to assess cortical excitability, voluntary activation was calculated using cortical twitch interpolation technique and sense of force was determined using constant-force sensation contractions. Main outcomes and results: The concussed group had lower intra-cortical facilitation (p = 0.036), lower maximal voluntary muscle activation (p = 0.038) and greater perceptions of force (p < 0.05), likely due to compensatory increases in upstream drive, than their healthy matched teammates. Conclusions: Taken together, these findings suggest a state of hypoexcitability that persists beyond the immediate acute phase of a concussion and may result in neuromuscular impairments that would call to question the athlete’s readiness to return to sport.

Behaviour and gaze analyses during a goal-directed locomotor task.

The objectives of the current study were: (a) to determine whether perception–action coupling controlled behaviours when walking through moving doors and (b) to determine how vision contributed to this behaviour. Participants (N = 6) walked along a 7-m path toward two motor-driven doors, which moved at rates ranging between 20 and 40 cm/s. Each door was independently driven such that both moved at the same velocity (symmetrical) or at different velocities (asymmetrical). The results showed that in both door movement conditions the participants controlled their approach velocity by slowing down prior to crossing the doors. The decrease in walking velocity produced greater velocity variability in the final stages prior to crossing the doors and high success rates. The results from the gaze behaviours showed that fixation durations were significantly longer when the doors moved asymmetrically, suggesting that the visual information from this unpredictable environment took longer to process. However, the fixation patterns were similar between the two door movement conditions. Regardless of the door movement condition, the participants spent about 60% of each trial fixating environmental objects (i.e., left door, right door, or aperture). The majority of fixations were directed towards one of the doors at the beginning of the trial and then shifted towards the aperture in the final phase. The participants were using perception–action coupling to control their behaviours in the final phase in order to steer locomotion through the aperture.

Task-specific modulations of locomotor action parameters based on on-line visual information during collision avoidance with moving objects

The objectives of this study were: (a) to determine if the control mechanism for interacting with a dynamic real environment is the same as in the virtual reality (VR) studies, and (b) to identify the action control parameters that are modulated to successfully pass through oscillating doors. The participants walked along a 14-m path towards oscillating doors (rate of change in aperture size = 44 cm/s and maximum aperture varied 70, 80, or 100 cm). The participants had to use vision to extrapolate what the aperture of the doors would be at the time of crossing and determine if a change in action parameters was necessary. If their current state did not match the required state then the participants made modifications to their actions. The results showed that individuals in a real environment used similar action modifications (i.e., velocity adjustments) as those seen in VR studies to increase success. Aside from the gradual velocity adjustments observed, there was an immergence of a different locomotor action parameter on some trials that was not seen in VR studies (i.e., shoulder rotations). These shoulder rotations occurred when the participants perceived that a velocity adjustment alone would not lead to a successful trial. These results show that participants use perception to control movement in a feedback rather than feedforward manner.

Action strategies of older adults walking through apertures.

The current study aimed to determine if the action strategies (i.e. Critical Point) of older adults when walking through apertures are different from those previously reported in young adults. Older adults (N=9) walked at a self selected pace along a 6-m path passing through a static door aperture (45-80 cm in 5 cm increments). Results showed that older adults rotate their shoulders more at apertures less than 1.6 times their shoulder width, indicating a more cautious approach. However, rotation magnitudes were highly variable at all aperture widths, but was not related to differences in stability. Therefore it appears that older adults use a body-scaled locomotor control strategy when passing through apertures.

Older adults are guided by their dynamic perceptions during aperture crossing.

Perceptions guide actions and these actions will affect perceptions (Gibson [1]). In return, these new perceptions will affect subsequent actions. The current study aimed to determine if the action differences previously observed in young and older adults are due to differences in perception and whether perceptual judgments guide action. Young (n=10) and older adults (n=9) completed two tasks; (1) judge the passability of various sized apertures during static and dynamic conditions and (2) physically pass through similar aperture sizes. The perceptual tasks required participants to give a yes/no response as to whether they could pass through an aperture (0.9-1.8 times SW (SW)) without rotating their shoulders from a distance of 5m from the aperture. During the passage through the aperture, the participants approached the aperture (1-1.8 times the SW) along a10m path at a self-selected pace and passed through the aperture using a suitable method. Results from the aperture crossing confirmed that older adults produce shoulder rotations at larger relative aperture widths than young adults and are more variable in their shoulder rotations at each aperture width. Perceptual results indicated that older adults had similar static but different dynamic perceptions than the young adults. The observed age-related differences in dynamic perceptions were most likely the result of differences in dynamic balance control.

Locomotor avoidance behaviours during a visually guided task involving an approaching object

Collision avoidance behaviours in situations where a collision may occur and ones planned movement is restricted, reveals that ones response is not as simple as a visual input producing some motor output. In this study, the participants (N=6) walked along a 9.5m path towards an air-filled human doll (180 degrees from their travel path) that would approach them on some trials. A spatial constraint (i.e. doorframe) was placed along the path and the participants had to determine if they could pass through the constraint prior to avoiding a collision or not. The constraint was set-up so that it was either at the theoretical collision point or 1.5m before or after the theoretical collision point. This study aimed to determine: (1) how the presence of a spatial constraint affects ones ability to perceive when to avoid a collision with an approaching object; (2) if the individuals use action parameters (i.e. velocity modifications, change in heading, etc.) in a consistent manner independent of the spatial constraint location and objects approach velocity; (3) if a consistent safety zone exists independent of the objects approach velocity. The results showed that the placement of the spatial constraint, but not the velocity of the object had a significant effect on the initiation of a change in heading. Participants used two-stage avoidance behaviour; change heading and then adjust walking velocity. The initial avoidance behaviour was initiated when the object was at a constant distance away (i.e. 3.73 m). Overall, it appears as though collision avoidance with approaching objects has cognitive as well as perceptual influences.

Gaze behavior during locomotion through apertures: the effect of locomotion forms.

The present study investigated spatio-temporal patterns of gaze fixations for passing safely through apertures. We focused on whether fixation patterns changed in response to changes in locomotion forms. Eight participants approached and passed through a narrow doorway using the following locomotion forms: normal walking, walking while holding a 63-cm horizontal bar with or without shoulder rotations permitted, and wheelchair use (63 cm wide). All participants were naïve to wheelchair use. The results showed that the fixation patterns were dependent on whether the locomotion form was walking or wheelchair use. In the three walking conditions, fixations were almost evenly directed toward the aperture and door edges at first; however, in the final phase, fixations were exclusively directed toward the center of the aperture. In contrast, in the wheelchair condition, fixations were directed more frequently toward the door edges throughout locomotion. These findings demonstrate that spatial-temporal patterns of fixation remain unchanged during walking through apertures, irrespective of the constraints on movement. The observed fixation patterns indicate that individuals appear to rely on optic flow to guide locomotion. However, the patterns of fixation are altered when they involve a completely novel task of locomotion, such as when using a wheelchair for the first time.

Involvement of the head and trunk during gaze reorientation during standing and treadmill walking

As individuals stand or walk in an environment their gaze may be reoriented from one location to another in response to auditory or visual stimuli. In order to reorient gaze, the eyes and/or the head and trunk must rotate. However, what determines the exact degree of rotation of each segment while standing or walking is not fully understood. In the current study we show that when participants were asked to reorient their gaze towards light cues positioned at eccentric locations of up to 90° while standing or walking on a treadmill their eyes and head mainly facilitated the action. Rotations of the head-in-space were similar for both tasks, but the rotation of the shoulders- and hips-in-space were lower for the treadmill walking condition. It is argued that this difference in the level of head-on-trunk rotation during the two tasks is controlled by the vestibular feedback loop. The regulation of this feedback loop is performed by the cerebellum in response to the level of threat to postural stability.

Dynamic stability and steering control following a sport-induced concussion

Loss of balance control is one of the cardinal symptoms following a concussion; however, the ability to detect the duration of these balance impairments seems to largely depend on task type and complexity. Typical balance assessment tools are simplistic and do not challenge dynamic balance control. Changing direction represents an internal perturbation that challenges the balance control system. The purpose of this study was to examine the effects of a concussion on dynamic stability and steering control. Nine male intercollegiate North American football players who experienced a concussion (CONC) were tested during the symptomatic phase (acute) and again once they had been cleared to return to play (RTP) while the controls (age- and position-matched teammates) were tested at a single time point coinciding with the acute phase testing of their matched injured player. All participants performed a steering task, requiring them to walk straight or turn in the direction of a visual cue located either 60° or 45° to the left or right of the centre line. CONC demonstrated increased swing time variability, segmental re-orientation variability, and the amount of time it took the centre of mass to reach the minimum lateral dynamic stability margin. These results suggest that CONC were more unstable and adopted a conservative gait strategy. Differences in the variability measures persisted even after the athlete was cleared to RTP. Overall, the findings reveal that intercollegiate football players with concussions have difficulty controlling temporal characteristics of gait, which cause dynamic instability to persist even at RTP.