Single-Task and Dual-Task Tandem Gait Performance Across Clinical Concussion Milestones in Collegiate Student-Athletes.

OBJECTIVE: To determine the length of time after concussion that impaired tandem gait performance is observed. DESIGN: Clinical measurement, prospective longitudinal. SETTING: NCAA collegiate athletic facility. PARTICIPANTS: Eighty-eight concussed NCAA Division I student-athletes and 30 healthy controls. INDEPENDENT VARIABLES: Group (concussion/control) and time (Baseline, Acute, Asymptomatic, and RTP). MAIN OUTCOME MEASURES: Participants completed 4 single-task and dual-task tandem gait trials. The concussion group completed tests at the following time points: preseason (Baseline), within 48 hours after concussion (Acute), on the day symptoms were no longer reported (Asymptomatic), and when cleared to return to sports (RTP). Controls completed the same protocol at similar intervals. The dual-task trials involved minimental style cognitive questions answered simultaneously during tandem gait. We analyzed the best time of the 4 trials, comparing groups with a linear mixed model. RESULTS: Acutely after concussion, the concussion group performed single-task tandem gait slower (worse) than controls (concussion: 11.36 ± 2.43 seconds, controls: 9.07 ± 1.78 seconds, P < 0.001). The concussion group remained significantly slower than controls (9.95 ± 2.21 vs 8.89 ± 1.65 seconds, P = 0.03) at Asymptomatic day but not RTP. There were significant group (P < 0.001) and time (P < 0.001) effects for dual-task tandem gait. The groups were not significantly different at baseline for single-task (P = 0.95) or dual-task (P = 0.22) tandem gait. CONCLUSIONS: Our results indicate that tandem gait performance is significantly impaired acutely after concussion, compared with both preseason measures and controls. Postural control impairments were not present when the student-athletes were cleared for RTP. This information can assist clinicians when assessing postural control and determining recovery after a concussive injury.

Anteroposterior balance reactions in children with spastic cerebral palsy.

AIM: To compare anterior and posterior standing balance reactions, as measured by single-stepping thresholds, in children with and without spastic cerebral palsy (CP). METHOD: Seventeen ambulatory children with spastic CP (eight males, nine females) and 28 typically developing children (13 males, 15 females; age range 5-12y, mean [SD] 9y 2mo [2y 3mo]), were included in this cross-sectional, observational study. Balance reaction skill was quantified as anterior and posterior single-stepping thresholds, or the treadmill-induced perturbations that consistently elicited a step in that direction. In order to understand the underlying mechanisms of between-group differences in stepping thresholds, dynamic stability was quantified using the minimum margin of stability. Ankle muscle activation latency, magnitude, and co-contraction were assessed with surface electromyography. RESULTS: We observed an age and group interaction for anterior thresholds (p=0.001, partial η2 =0.24). At older (≈11y; p<0.001, partial η2 =0.48), but not younger (≈7y; p=0.33, partial η2 =0.02) ages, typically developing children had larger anterior thresholds than those with CP. In response to near-threshold anterior perturbations, older typically developing children recovered from more instability than their peers with CP (p=0.004, partial η2 =0.18). Older children had no between-group differences in ankle muscle activity. No between-group differences were observed in posterior thresholds. INTERPRETATION: The effects of CP on balance reactions are age- and direction-specific. Older typically developing children are more able or willing to withhold a step when unstable. WHAT THIS PAPER ADDS: Children with spastic cerebral palsy have age- and direction-specific balance-reaction impairments. Lower anterior stepping thresholds were observed in older, but not younger children. Older typically developing children withheld a forward step at higher levels of instability. No between-group differences were seen in posterior stepping thresholds.

Posterior single-stepping thresholds are prospectively related to falls in older women.

BACKGROUND: Falls are a leading cause of injury in older women. Stepping thresholds quantify balance-reaction capabilities. It is unclear how such evaluations predict falls in comparison to, or as a complement to, other objective measures of gait, standing postural control, strength, and balance confidence. AIMS: The objective of this study was to determine if stepping thresholds are prospectively related to falls in older women. METHODS: For this prospective cohort study, 125 ambulatory, community-dwelling women, age ≥ 65 years were recruited. Using a treadmill to deliver perturbations to standing participants, we determined anteroposterior single- and multiple-stepping thresholds. Here, thresholds represent the minimum perturbation magnitudes that consistently evoke one step or multiple steps. In addition, gait kinematics, obstacle-crossing kinematics, standing sway measures, unipedal stance time, the functional reach, lower extremity isometric strength, grip strength, balance confidence, and fall history were evaluated. Falls were prospectively recorded for one year. RESULTS: Seventy-four participants (59%) fell at least once. Posterior single-stepping thresholds were the only outcome that predicted future fall status (OR = 1.50, 95% CI 1.01-2.28; AUC = .62). A multivariate approach added postural sway with eyes closed as a second predictive variable, although predictive abilities were not meaningfully improved. DISCUSSION: These results align with the previous evidence that reactive balance is a prospective indicator of fall risk. Unlike previous studies, strength scaled to body size did not contribute to fall prediction. CONCLUSION: Posterior single-stepping thresholds held a significant relationship with future fall status. This relationship was independent of, and superior to that of, other measures of standing balance, gait, strength, and balance confidence.

The development and feasibility of treadmill-induced fall recovery training applied to individuals with chronic stroke.

BACKGROUND: Exercise has failed to reduce falls in those with chronic stroke. A limitation of traditional exercise is that the motor responses needed to prevent a fall are not elicited (i.e. they lack processing specificity). Balance reactions often require compensatory steps. Therefore, interventions that target such steps have the potential to reduce falls. Computerized treadmills can deliver precise, repeatable, and challenging perturbations as part of a training protocol. The objective of this study was to develop and determine the feasibility of such training applied to those with chronic stroke. We developed the training to address specificity, appropriate duration and repetition, and progressive overloading and individualization. We hypothesized that our intervention would be acceptable, practical, safe, and demonstrate initial signs of efficacy. METHODS: In this single-arm study, thirteen individuals with chronic stroke (29-77 years old, 2-15 years post stroke) performed up to six training sessions using a computer-controlled treadmill. Each session had separate progressions focused on initial steps with the non-paretic or paretic limbs in response to anterior or posterior falls. Perturbation magnitudes were altered based on performance and tolerance. Acceptability was determined by adherence, or the number of sessions completed. Practicality was documented by the equipment, space, time, and personnel. Adverse events were documented to reflect safety. In order to determine the potential-efficacy of this training, we compared the proportion of successful recoveries and the highest perturbation magnitude achieved on the first and last sessions. RESULTS: The training was acceptable, as evident by 12/13 participants completing all 6 sessions. The protocol was practical, requiring one administrator, the treadmill, and a harness. The protocol was safe, as evident by no serious or unanticipated adverse events. The protocol demonstrated promising signs of efficacy. From the first to last sessions, participants had a higher proportion of successful recoveries and progressed to larger disturbances. CONCLUSIONS: Using a computerized treadmill, we developed an approach to fall-recovery training in individuals with chronic stroke that was specific, considered duration and repetition, and incorporated progressive overloading and individualization. We demonstrated that this training was acceptable, practical, safe, and potentially beneficial for high-functioning individuals with chronic stroke. TRIAL REGISTRATION: Retrospectively registered at clinicaltrials.gov ( NCT03638089 ) August 20, 2018.

Effect of heterotopic ossification on hip range of motion and clinical outcome.

The utility of heterotopic ossification (HO) classification systems is debatable. The range of motion and Harris hip score (HHS) were calculated in 104 patients with known HO after total hip arthroplasty and 208 matched controls without HO. The patients with HO were radiographically divided into high and low grade HO groups. There was no statistically significant association of HHS with high or low grade HO. High grade HO had a statistically significant 6° loss of terminal hip flexion, 4° loss of abduction, and 6° loss of internal rotation at the hip. The small changes in terminal hip range of motion and lack of association with HHS may be the result of false radiographic continuity resulting in an overestimation of the disability in high grade HO.

Exercise-based fall prevention: can you be a bit more specific?

Trip-specific perturbation training reduces trip-related falls after laboratory-induced trips and, prospectively, in the community. Based on an emerging body of evidence, we hypothesize that using task-specific perturbation training as a stand-alone approach or in conjunction with conventional exercise-based approaches will improve the effectiveness of fall prevention interventions significantly.

Does the effect of walking balance perturbations generalize across contexts?

Balance perturbations are used to study locomotor instability. However, these perturbations are designed to provoke a specific context of instability that may or may not generalize to a broader understanding of falls risk. The purpose of this study was to determine if the effect of balance perturbations on instability generalizes across contexts. 29 younger adults and 28 older adults completed four experimental trials, including unperturbed walking and walking while responding to three perturbation contexts: mediolateral optical flow, treadmill-induced slips, and lateral waist-pulls. We quantified the effect of perturbations as an absolute change in margin of stability from unperturbed walking. We found significant changes in mediolateral and anteroposterior margin of stability for all perturbations compared to unperturbed walking in both cohorts (p-values ≤ 0.042). In older adults, the mediolateral effects of lateral waist-pulls significantly correlated with those of optical flow perturbations and treadmill-induced slips (r ≥ 0.398, p-values ≤ 0.036). In younger adults but not in older adults, we found positive and significant correlations between the anteroposterior effect of waist-pull perturbations and optical flow perturbations, and the anteroposterior and mediolateral effect of treadmill-induced slips (r ≥ 0.428, p-values ≤ 0.021). We found no "goldilocks" perturbation paradigm to endorse that would support universal interpretations about locomotor instability. Building the most accurate patient profiles of instability likely requires a series of perturbation paradigms designed to emulate the variety of environmental contexts in which falls may occur.

Immediate and Short-Term Effects of In-Shoe Heel-Lift Orthoses on Clinical and Biomechanical Outcomes in Patients With Insertional Achilles Tendinopathy.

Background: Physical therapists frequently employ heel lifts as an intervention to reduce Achilles tendon pain and restore function. Purpose: To determine the short-term effect of heel lifts on clinical and gait outcomes in participants with insertional Achilles tendinopathy (IAT). Study Design: Case series; Level of evidence, 4. Methods: Participants with IAT underwent eligibility screening and completed assessments at baseline and 2 weeks later. Primary outcomes included symptom severity (Victoria Institute of Sports Assessment-Achilles [VISA-A]), gait analysis with the 10-m walk-test at 2 speeds (normal and fast), and pain during walking. Pain and gait analysis were assessed under 3 conditions: before fitting 20-mm heel lifts, immediately after heel-lift fitting, and after 2 weeks of wearing heel lifts. Ultrasound images and measurements at the Achilles insertion were obtained from prone and standing positions (with and without heel lifts). Spatiotemporal gait parameters and tibial tilt angles were evaluated at normal speed using inertia measurement units during the 3 study conditions. Differences between the conditions were analyzed using paired t test or analysis of variance. Results: Overall, 20 participants (12 female, 13 with bilateral IAT; mean age, 51 ± 9.3 years; mean body mass index 31.6 ± 6.8 kg/m2) completed all assessments. Symptom severity (VISA-A) of the more symptomatic side significantly improved at 2 weeks (60 ± 20.6) compared with baseline (52.2 ± 20.4; P < .01). Pain during gait (Numeric Pain Rating Scale) was significantly reduced immediately after heel-lift fitting (0.7 ± 2.0) when compared with baseline (2.2 ± 2.7, P = .043). Spatiotemporal gait parameters and tibial tilt angle before and after using heel lifts at normal walking speed were not significantly different; however, gait speed, stride length, and tibial tilt angle on both sides increased significantly immediately after using heel lifts and were maintained after 2 weeks of wear. Conclusion: Using heel lifts not only improved symptom severity after 2 weeks but also immediately reduced pain during gait and had a positive impact on gait pattern and speed.

A pelvis-oriented margin of stability is robust against deviations in walking direction.

The Margin of Stability (MOS) is often assessed relative to the intended, linear path of walking progression. When an unanticipated or irregular change in direction occurs, such as during a sudden turn or during activities of daily living, distinguishing the lateral from anteroposterior MOS can be challenging. The purpose of this study was to assess an anatomically orientated method of calculating the MOS using the pelvic orientation to define lateral and anteroposterior directions. We hypothesized that when straight walking was disrupted with a curved path, the pelvis-oriented MOS measure would be less variable compared to the global-oriented MOS measure. We recruited 16 unimpaired participants to walk at preferred and fast walking speeds along a straight walking path, as well as a path with an exaggerated, curvilinear deviation. We determined the within-subject mean and standard deviation of the anterior MOS at mid-swing and the posterior and lateral MOS at ipsilateral foot strike. For straight walking and curved walking separately, repeated measures factorial ANOVAs assessed the effects of model (global or pelvis-oriented), limb (left or right), and speed (preferred or fast) on these MOS values. Based on reduced variability during curved walking, the pelvis-oriented MOS was more robust to walking deviations than the globally defined MOS. In straight walking, the pelvis-oriented MOS was characterized by less lateral and more anterior stability with differences exacerbated by faster walking. These results suggest a pelvis-oriented MOS has utility when the path of progression is unknown or unclear.

Susceptibility to walking balance perturbations in young adults is largely unaffected by anticipation.

Despite progress in understanding the mechanisms governing walking balance control, the number of falls in our older adult population is projected to increase. Falls prevention systems and strategies may benefit from understanding how anticipation of a balance perturbation affects the planning and execution of biomechanical responses to mitigate instability. However, the extent to which anticipation affects the proactive and reactive adjustments to perturbations has yet to be fully investigated, even in young adults. Our purpose was to investigate the effects of anticipation on susceptibility to two different mechanical balance perturbations - namely, treadmill-induced perturbations and impulsive waist-pull perturbations. Twenty young adults (mean ± standard deviation age: 22.8 ± 3.3 years) walked on a treadmill without perturbations and while responding to treadmill belt (200 ms, 6 m/s2) and waist-pull (100 ms, 6% body weight) perturbations delivered in the anterior and posterior directions. We used 3D motion capture to calculate susceptibility to perturbations during the perturbed and preceding strides via whole-body angular momentum (WBAM) and anterior-posterior margin of stability (MoSAP). Contrary to our hypotheses, anticipation did not affect young adults' susceptibility to walking balance challenges. Conversely, perturbation direction significantly affected walking instability. We also found that susceptibility to different perturbation contexts is dependent on the outcome measure chosen. We suggest that the absence of an effect of anticipation on susceptibility to walking balance perturbations in healthy young adults is a consequence of their having high confidence in their reactive balance integrity. These data provide a pivotal benchmark for the future identification of how anticipation of a balance challenge affects proactive and reactive balance control in populations at risk of falls.

A novel method to quantify individual limb contributions to standing postural control.

BACKGROUND: Understanding individual limb contributions to standing postural control is valuable when evaluating populations with asymmetric function (e.g., stroke, amputations). We propose a method of quantifying three contributions to controlling the net anteroposterior center of pressure (CoP) during quiet standing: CoP moving under left and right limbs and weight shifting between the two limbs. RESEARCH QUESTION: Can these contributions to standing postural control be quantified from CoP trajectories in neurotypical adults? METHODS: Instantaneous contributions can be negative or larger than one, and integrated contributions sum to equal one. Proof-of-concept demonstrations validated these calculated contributions by restricting CoP motion under one or both feet. We evaluated these contributions in 30 neurotypical young adults who completed two (eyes opened; eyes closed) 30-s trials of bipedal standing. We evaluated the relationships between limb contributions, self-reported limb dominance, and between-limb weight distributions. RESULTS: All participants self-reported as right-limb dominant; however, a range of mean limb contributions were observed with eyes opened (Left: mean [range] = 0.52 [0.37-0.63]; Right: 0.48 [0.31-0.63]) and with eyes closed (Left: 0.51 [0.39-0.63]; Right: 0.49 [0.37-0.61]). Weight-shift contributions were small with eyes opened (0.00 [-0.01 to 0.01]) and eyes closed (0.00 [-0.01 to 0.02]). We did not identify any between-limb differences in contributions when grouped by self-reported limb dominance (p > 0.10, d < 0.31). Contributions did not significantly correlate with Waterloo Footedness scores (-0.22 < r < 0.21, p > 0.25) or between-limb weight distributions (0 < r < 0.24, p > 0.20). SIGNIFICANCE: Across neurotypical participants, we observed a notable range of limb contributions not related to self-reported limb dominance or between-limb weight distributions. With this tool, we can characterize differences in the amount of CoP motion and the underlying control strategies. Changes in limb contribution can be measured longitudinally (i.e., across rehabilitation programs, disease progression, aging) representative of limb function, which may be particularly useful in populations with asymmetric function.

Treadmill-based system for postural studies: Design and validation.

Computer-controlled treadmills are common in many gait labs and offer great potential for conducting perturbation-based postural studies. However, the time-course of these disturbances can be too brief to be controlled manually through product software. Here we present a system that combines a Bertec® split-belt treadmill with custom hardware and software to deliver postural disturbances during standing and record data from multiple sources simultaneously. We used this system to administer to 15 healthy participants an 8-session perturbation-based training protocol in which they learned to respond without stepping to progressively larger perturbations. Kinematic, electromyographic, and force data were collected throughout. Motion capture was used to characterize the accuracy and repeatability of the treadmill-delivered perturbations with respect to duration, displacement, and peak velocity. These (observed) data were compared to that expected based on software commands and the known constraints of the treadmill (i.e., 10 Hz operating speed). We found perturbation durations to be as expected. Peak velocities and displacements were slightly higher than expected (average increases were 0.59 cm/s and 1.76 cm, respectively). Because this increase in magnitude was consistent, it did not impede training or affect data analysis. Treadmill behavior was repeatable across 95 % of trials.

How should the margin of stability during walking be expressed to account for body size?

When expressing the margin of stability as a distance, it does not directly estimate the perturbation magnitude needed to change stability states. Additionally, it is unknown how body size may influence this measure. Therefore, we propose other expressions of stability margins, including that of an impulse, a change in center of mass velocity, and a scaled, unitless impulse. The purpose of this study was to determine the influence of body size on these margin expressions using walking data from children and adults. We anticipated that margins expressed as an impulse would have strong correlations with body mass and height, as well as large between-group differences. We predicted that scaling this impulse value would result in small correlations and between-group effect sizes. We calculated each stability margin at minimum lateral values and in the anteroposterior directions at mid-swing and foot strike. In the lateral direction, margins expressed as an impulse had strong correlations with body size (r≥0.58, p<0.01) and large between-group differences (|d|≥1.07, p<0.01). The other expressions did not have strong positive correlations (|r|≤0.20) or large between-group effects (|d|≤0.44). In the anteroposterior directions, impulse margins had strong correlations with body size (|r|≥0.83, p<0.01) and large between-group differences (|d|≥1.74, p<0.01). The scaled, unitless impulse margin was the only variable that resulted in small, non-significant differences (|r|≤0.22, p≥0.24) as well as small between-group effect sizes (|d|≤0.46, p≥0.22). We propose expressing stability margins as an impulse. If scaling is needed, we encourage using the scaled, unitless impulse.

Association Between Collision Sport Career Duration and Gait Performance in Male Collegiate Student-Athletes.

BACKGROUND: Investigations of estimated age of first exposure to repetitive head impacts from collision and contact sports have shown no associations with neurocognitive or neurobehavioral function at the collegiate level, but the effect of career duration may be a more comprehensive factor. Understanding whether longer career duration influences gait performance would provide insights into potential neurological impairment. PURPOSE: To examine the relationship between career duration of collision sports and single/dual-task gait performance in collegiate student-athletes. STUDY DESIGN: Cross-sectional study; Level of evidence, 3. METHODS: We recruited 168 male student-athletes from collision sports: football, lacrosse, ice hockey, and wrestling (mean ± SD age, 19.2 ± 1.3 years; height, 184.5 ± 7.2 cm; mass, 94.3 ± 15.9 kg; estimated age of first exposure, 8.6 ± 3.1 years; career duration, 10.6 ± 3.0 years). All participants completed a baseline single- and dual-task gait assessment before the start of their athletic season. Inertial measurement units were used to measure gait speed and stride length. During the dual task, participants were asked to perform working memory cognitive tasks while walking. The dependent variables were single/dual-task gait speed and stride length, cognitive accuracy, and dual-task cost. The relationship between career duration, analyzed as a continuous variable, and the dependent variables was analyzed using a linear regression. RESULTS: There were no significant associations between career duration and single-task gait speed (1.16 ± 0.16 m/s; ß = -0.004; P = .35; 95% CI = -0.012 to 0.004; η2 = 0.005) or dual-task gait speed (1.02 ± 0.17 m/s; ß = -0.003; P = .57; 95% CI = -0.011 to 0.006; η2 = 0.002). There were also no significant associations between career duration and single/dual-task stride length, cognitive accuracy, or dual-task cost. CONCLUSION: Career duration among collegiate collision sport athletes was not associated with single- or dual-task gait performance, suggesting that a greater exposure to repetitive head impacts is not detrimental to dynamic postural control at the college level. However, the effects of diminished gait performance over the lifetime remain to be elucidated.

Falling risk in patients with end-stage knee osteoarthritis.

Although 25% of patients with end-stage knee osteoarthritis (OA) have reported a fall, there is limited information about risk factors for falling in patients awaiting total knee arthroplasty (TKA). The purpose of this study was to identify clinical and functional measures related to fall risk. A total of 259 participants awaiting TKA for OA participated in this secondary cross-sectional study. Participants were divided into fallers and non-fallers based on falling history in the prior 6 months. Clinical measures (hip and knee pain, neck and low back pain (LBP), knee range of motion, and quadriceps strength) and functional measures (six-minute walk test (6MWT), timed up and go test, and Knee Injury and Osteoarthritis Outcome Score (KOOS)) were assessed in patients 2-4 weeks prior to TKA. Independent t tests were used to examine differences between groups. Odds ratio was calculated to identify clinical risk factors for falling. Of all participants, 47 (18%) reported a fall in the previous 6 months. Fallers had 30% greater LBP (3.0 ± 2.5 vs. 2.1 ± 2.6; p = 0.025). Fallers walked 12% shorter distance in the 6MWT than non-fallers (378 ± 100 vs. 422 ± 105 m; p = 0.010). For every 1-point increase in LBP on a 0-10 scale, there was a 14% greater risk of falling (p = 0.028). For every 10-m increase in 6MWT, there was a 3.8% reduction in fall risk (p = 0.011). Greater LBP and worse walking endurance are associated with falls in individuals with end-stage OA. Future studies should determine if interventions that reduce LBP and improve walking performance also reduce the chance of falling.

Posterior fall-recovery training applied to individuals with chronic stroke: A single-group intervention study.

BACKGROUND: To assess the effects of the initial stepping limb on posterior fall recovery in individuals with chronic stroke, as well as to determine the benefits of fall-recovery training on these outcomes. METHODS: This was a single-group intervention study of 13 individuals with chronic stroke. Participants performed up to six training sessions, each including progressively challenging, treadmill-induced perturbations from a standing position. Progressions focused on initial steps with the paretic or non-paretic limb. The highest perturbation level achieved, the proportion of successful recoveries, step and trunk kinematics, as well as stance-limb muscle activation about the ankle were compared between the initial stepping limbs in the first session. Limb-specific outcomes were also compared between the first and last training sessions. FINDINGS: In the first session, initial steps with the non-paretic limb were associated with a higher proportion of success and larger perturbations than steps with the paretic limb (p = 0.02, Cohen's d = 0.8). Paretic-limb steps were wider relative to the center of mass (CoM; p = 0.01, d = 1.3), likely due to an initial standing position with the CoM closer to the non-paretic limb (p = 0.01, d = 1.4). In the last training session, participants recovered from a higher proportion of perturbations and advanced to larger perturbations (p < 0.05, d > 0.6). There were no notable changes in kinematic or electromyography variables with training (p > 0.07, d < 0.5). INTERPRETATION: The skill of posterior stepping in response to a perturbation can be improved with practice in those with chronic stroke, we were not able to identify consistent underlying kinematic mechanisms behind this adaptation.

The construct and concurrent validity of brief standing sway assessments in children with and without cerebral palsy.

BACKGROUND: Standing postural sway is often quantified from center of pressure trajectories. During assessments of longer durations, children may fidget, thus limiting the feasibility and validity of sway recordings. RESEARCH QUESTION: Do postural sway sample durations less than 30 s maintain construct and concurrent validity? METHODS: In this case-control, observational study, we measured postural sway in 41 children (age 5-12 years, 23 typically developing (TD); 18 with spastic cerebral palsy (CP), 13 diplegic and 5 hemiplegic, 11 GMFCS level I and 7 level II) for 30-second eyes-opened and eyes-closed conditions. From a single recording, 5-second incremental durations of 5-30 s were considered in this analysis. We quantified anteroposterior, mediolateral, and transverse-plane sway using seven time-domain variables: root-mean-square error, total excursion, mean frequency, mean distance, sway area, and 95 % confidence circle and ellipse areas. Variables were calculated in eyes-opened and eyes-closed conditions, as well as the ratio of the two. Construct validity was evaluated by the persistence of large effect sizes (Glass's Δ ≥ 0.80) between CP and TD participants at shorter durations than 30 s. Concurrent validity was evaluated by the correlations of shorter duration measures to the 30 s measure. RESULTS: Seven sway measures had large between-group effects (Glass's Δ ≥ 1.02) for the 30 s measure that persisted (Glass's Δ ≥ 0.81) at shorter durations (5-25 s) and also maintained concurrent validity (r ≥ 0.83). Six of these seven measures were taken in the eyes-closed condition, and all seven measures were in the mediolateral direction or transverse plane. SIGNIFICANCE: Our analysis suggests that sway durations less than 30 s can uphold construct and concurrent validity. These measures were primarily in the eyes-closed conditions and mediolateral direction. These results are a promising indicator that shorter-duration sway measures may be of utility when fidgeting prevents longer recordings.

Gait Performance Is Associated with Subsequent Lower Extremity Injury following Concussion.

PURPOSE: The purpose was to examine gait characteristics between collegiate athletes who did and did not sustain a lower-extremity musculoskeletal (LEMSK) injury in the year after concussion. METHODS: Thirty-four NCAA collegiate athletes with diagnosed concussions were divided into two groups based on if they did (n = 16) or did not (n = 18) sustain a LEMSK in the year after concussion. Participants completed baseline testing before the start of the season and again at return to play postconcussion. Injuries were tracked using an electronic medical database. Participants were instrumented with three APDM Opal triaxial accelerometers and performed five single-task (ST) and five dual-task (DT) gait trials. Participants traversed a 10-meter walkway, turned around a specified endpoint, and returned to the original line. During DT, participants simultaneously walked and answered mini-mental style questions. A linear mixed-effects model assessed interactions and/or main effects between groups for gait speed, double support time, cadence, stride length, and cognitive accuracy. RESULTS: The LEMSK group walked slower (ST, 1.15 ± 0.10 m·s; DT, 1.01 ± 0.10 m·s) than the uninjured group (ST, 1.23 ± 0.11 m·s; DT, 1.10 ± 0.11 m·s) during both ST (P = 0.04) and DT (P = 0.03). The injury group spent longer in double support (ST, 20.19% ± 2.34%; DT, 21.92% ± 2.13%) than the uninjured group (ST, 18.16% ± 2.60%; DT, 20.00% ± 2.32%) during both ST (P = 0.02) and DT (P = 0.02). The injury group had a significantly lower cognitive accuracy (89.56% ± 6.48%) than the uninjured group (95.40% ± 7.08%) across time points (P = 0.02). CONCLUSIONS: There were significant differences in gait characteristics and cognitive accuracy between those who did and did not sustain a LEMSK injury after concussion. The LEMSK group demonstrated a conservative gait strategy both before and after their concussive injury.

Relationships of Linear and Non-linear Measurements of Post-stroke Walking Activity and Their Relationship to Weather.

Background: Stroke survivors are more sedentary than the general public. Previous research on stroke activity focuses on linear quantities. Non-linear measures, such as Jensen-Shannon Divergence and Lempel-Ziv Complexity, may help explain when and how stroke survivors move so that interventions to increase activity may be designed more effectively. Objectives: Our objective was to understand what factors affect a stroke survivor's physical activity, including weather, by characterizing activity by step counts, structure, and complexity. Methods: A custom MATLAB code was used to analyze clinical trial (NCT02835313, https://clinicaltrials.gov/ct2/show/NCT02835313) data presented as minute by minute step counts. Six days of data were analyzed for 142 participants to determine the regularity of activity structure across days and complexity patterns of varied cadences. The effect of steps on structure and complexity, the season's effect on steps, structure, and complexity, and the presence of precipitation's effect on steps and complexity were all analyzed. Results: Step counts and regularity were linearly related (p < 0.001). Steps and complexity were quadratically related (r 2 = 0.70 for mean values, 0.64 for daily values). Season affected complexity between spring and winter (p = 0. 019). Season had no effect on steps or structure. Precipitation had no effect on steps or complexity. Conclusions: Stroke survivors with high step counts are active at similar times each day and have higher activity complexities as measured through patterns of movement at different intensity levels. Non-linear measures, such as Jensen-Shannon Divergence and Lempel-Ziv Complexity, are valuable in describing a person's activity. Weather affects our activity parameters in terms of complexity between spring and winter.

Brain Stiffness Relates to Dynamic Balance Reactions in Children With Cerebral Palsy.

Cerebral palsy is a neurodevelopmental movement disorder that affects coordination and balance. Therapeutic treatments for balance deficiencies in this population primarily focus on the musculoskeletal system, whereas the neural basis of balance impairment is often overlooked. Magnetic resonance elastography (MRE) is an emerging technique that has the ability to sensitively assess microstructural brain health through in vivo measurements of neural tissue stiffness. Using magnetic resonance elastography, we have previously measured significantly softer grey matter in children with cerebral palsy as compared with typically developing children. To further allow magnetic resonance elastography to be a clinically useful tool in rehabilitation, we aim to understand how brain stiffness in children with cerebral palsy is related to dynamic balance reaction performance as measured through anterior and posterior single-stepping thresholds, defined as the standing perturbation magnitudes that elicit anterior or posterior recovery steps. We found that global brain stiffness is significantly correlated with posterior stepping thresholds (P = .024) such that higher brain stiffness was related to better balance recovery. We further identified specific regions of the brain where stiffness was correlated with stepping thresholds, including the precentral and postcentral gyri, the precuneus and cuneus, and the superior temporal gyrus. Identifying brain regions affected in cerebral palsy and related to balance impairment can help inform rehabilitation strategies targeting neuroplasticity to improve motor function.