The Influence of a Booster Seat on the Motion of the Reclined Small Female Anthropomorphic Test Device in Low-Acceleration Far-Side Lateral Oblique Impacts.

Belt-positioning booster (BPB) seats may prevent submarining in reclined child occupants in frontal impacts. BPB-seated child volunteers showed reduced lateral displacement in reclined seating in low-acceleration lateral-oblique impacts. As submarining was particularly evident in reclined small adult female occupants, we examined if a booster seat could provide similar effects on the kinematics of the small female occupant to the ones found on the reclined child volunteers in low-acceleration far-side lateral oblique impacts. The THOR-AV-5F was seated on a vehicle seat on a sled simulating a far-side lateral-oblique impact (80 deg from frontal, maximum acceleration ∼2 g, duration ∼170 ms). Lateral and forward head and trunk displacements, trunk rotation, knee-head distance, seatbelt loads, and head acceleration were recorded. Three seatback angles (25 deg, 45 deg, 60 deg) and two booster conditions were examined. Lateral peak head and trunk displacements decreased in more severe reclined seatback angles (25-36 mm decrease compared to nominal). Forward peak head, trunk displacements, and knee-head distance were greater with the seatback reclined and no BPB. Knee-head distance increased in the severe reclined angle also with the booster seat (>40 mm compared to nominal). Seat belt peak loads increased with increased recline angle with the booster, but not without the booster seat. Booster-like solutions may be beneficial for reclined small female adult occupants to reduce head and trunk displacements in far-side lateral-oblique impacts, and knee-head distance and motion variability in severe reclined seatback angles.

Impaired Neuromotor Control During Gait in Concussed Adolescents-A Frequency Analysis.

Disruptions in gait function are common after concussion in adolescents; however, the neuromotor control deficits driving these gait disruptions are not well known. Fifteen concussed (age mean [SD]): 17.4 [0.6], 13 females, days since injury: 26.3 [9.9]) and 17 uninjured (age: 18.0 [0.7], 10 females) adolescents completed 3 trials each of single-task gait and dual-task gait (DT). During DT, participants simultaneously walked while completing a serial subtraction task. Gait metrics and variability in instantaneous mean frequency in lower extremity muscles were captured by inertial sensors and surface electromyography, respectively. A 2-way analysis of covariance was used to compare gait metrics across groups and conditions. Functional principal components analysis was used to identify regions of variability in instantaneous mean frequency curves. Functional principal component scores were compared across groups using a Welch statistic. Both groups displayed worse performance on gait metrics during DT condition compared to single-task, with no differences between groups (P < .001). Concussed adolescents displayed significantly greater instantaneous mean frequency, indicated by functional principal component 1, in the tibialis anterior, biceps femoris, and semitendinosus (P < .05) during single-task and DT compared with uninjured adolescents. Our observations suggest that concussed adolescents display inefficient motor unit recruitment lasting longer than 2 weeks following injury, regardless of the addition of a secondary task.

Dynamic Balanced Reach: A Temporal and Spectral Analysis Across Increasing Performance Demands.

Standing balanced reach is a fundamental task involved in many activities of daily living that has not been well analyzed quantitatively to assess and characterize the multisegmental nature of the body's movements. We developed a dynamic balanced reach test (BRT) to analyze performance in this activity; in which a standing subject is required to maintain balance while reaching and pointing to a target disk moving across a large projection screen according to a sum-of-sines function. This tracking and balance task is made progressively more difficult by increasing the disk's overall excursion amplitude. Using kinematic and ground reaction force data from 32 young healthy subjects, we investigated how the motions of the tracking finger and whole-body center of mass (CoM) varied in response to the motion of the disk across five overall disk excursion amplitudes. Group representative performance statistics for the cohort revealed a monotonically increasing root mean squared (RMS) tracking error (RMSE) and RMS deviation (RMSD) between whole-body CoM (projected onto the ground plane) and the center of the base of support (BoS) with increasing amplitude (p < 0.03). Tracking and CoM response delays remained constant, however, at 0.5 s and 1.0 s, respectively. We also performed detailed spectral analyses of group-representative response data for each of the five overall excursion amplitudes. We derived empirical and analytical transfer functions between the motion of the disk and that of the tracking finger and CoM, computed tracking and CoM responses to a step input, and RMSE and RMSD as functions of disk frequency. We found that for frequencies less than 1.0 Hz, RMSE generally decreased, while RMSE normalized to disk motion amplitude generally increased. RMSD, on the other hand, decreased monotonically. These findings quantitatively characterize the amplitude- and frequency-dependent nature of young healthy tracking and balance in this task. The BRT is not subject to floor or ceiling effects, overcoming an important deficiency associated with most research and clinical instruments used to assess balance. This makes a comprehensive quantification of young healthy balance performance possible. The results of such analyses could be used in work space design and in fall-prevention instructional materials, for both the home and work place. Young healthy performance represents "exemplar" performance and can also be used as a reference against which to compare the performance of aging and other clinical populations at risk for falling.

A new methodological approach to characterize selective motor control in children with cerebral palsy.

Introduction: Despite being a primary impairment in individuals with cerebral palsy (CP), selective motor control (SMC) is not routinely measured. Personalized treatment approaches in CP will be unattainable without the ability to precisely characterize the types and degrees of impairments in motor control. The objective of this study is to report the development and feasibility of a new methodological approach measuring muscle activation patterns during single-joint tasks to characterize obligatory muscle co-activation patterns that may underly impaired SMC. Methods: Muscle activation patterns were recorded during sub-maximal voluntary isometric contraction (sub-MVIC) tasks at the hip, knee, and ankle with an interactive feedback game to standardize effort across participants. We calculated indices of co-activation, synergistic movement, mirror movement, and overflow (indices range 0-2, greater scores equal to greater impairment in SMC) for each isolated joint task in 15 children - 8 with typical development (TD) (mean age 4.7 ± 1.0 SD years) and 7 with CP (mean age 5.8 ± 0.7 SD years). Indices were compared with Mann-Whitney tests. The relationships between the indices and gross motor function (GMFM-66) were examined with Pearson's r. Results: Mean indices were higher in the CP vs. the TD group for each of the six tasks, with mean differences ranging from 0.05 (abduction and plantarflexion) to 0.44 (dorsiflexion). There was great inter-subject variability in the CP group such that significant group differences were detected for knee flexion mirroring (p = 0.029), dorsiflexion coactivation (p = 0.021), and dorsiflexion overflow (p = 0.014). Significant negative linear relations to gross motor function were found in all four indices for knee extension (r = -0.56 to -0.75), three of the indices for ankle dorsiflexion (r = -0.68 to -0.78) and in two of the indices for knee flexion (r = -0.66 to -0.67), and ankle plantarflexion (r = -0.53 to -0.60). Discussion: Indices of coactivation, mirror movement, synergy, and overflow during single-joint lower limb tasks may quantify the type and degree of impairment in SMC. Preliminary concurrent validity between several of the indices of SMC and gross motor function was observed. Our findings established the feasibility of a new methodological approach that quantifies muscle activation patterns using electromyography paired with biofeedback during single-joint movement.

The effect of reclined seatback angles on the motion of booster-seated children during lateral-oblique low-acceleration impacts.

Belt-positioning boosters (BPB) may prevent submarining in novel seating configurations such as seats with reclined seatbacks. However, several knowledge gaps in the motion of reclined child occupants remain as previous reclined child studies only examined responses of a child anthropomorphic test device (ATD) and the PIPER finite element (FE) model in frontal impacts. The aim of this study is to investigate the effect of reclined seatback angles and two types of BPBs on the motion of child volunteer occupants in low-acceleration far-side lateral-oblique impacts. Six healthy children (3 males, 3 females, 6-8 years, seated height: 66±3.2 cm, weight: 25.2±3.2 kg) were seated on two types of low-back BPB (standard and lightweight) on a vehicle seat and restrained by a 3-point simulated-integrated seatbelt on a low-acceleration sled. The sled exposed the participants to a low-speed lateral-oblique (80° from frontal) pulse (2 g). Three seatback recline angles (25°, 45°, 60° from vertical) with two BPB (standard and lightweight) were tested. A 10-camera 3D-motion-capture system (Natural Point Inc.) was used to capture peak lateral head and trunk displacements and forward knee-head distance. Three seat-belt load cells (Denton ATD Inc) captured peak seatbelt loads. Electromyography (EMG, Delsys Inc) recorded muscle activation. Repeated Measure 2-way ANOVAs were performed to evaluate the effect of seatback recline angle and BPB on kinematics. Tukey's post-hoc test for pairwise comparisons was used. P-level was set to 0.05. Peak lateral head and trunk displacement decreased with the increasing seatback recline angle (p < 0.005, p < 0.001, respectively). Lateral peak head displacement was greater in the 25° compared to the 60° condition (p < 0.002) and in the 45° condition compared to the 60° condition (p < 0.04). Lateral peak trunk displacement was greater in the 25° condition than the 45° condition (p < 0.009) and the 60° condition (p < 0.001), and in the 45° condition than the 60° condition (p < 0.03). Overall peak lateral head and trunk displacements and knee-head forward distance were slightly greater in the standard than the lightweight BPB (p < 0.04), however these differences between BPBs were small (∼10 mm). Shoulder belt peak load decreased as the reclined seatback angle increased (p < 0.03): the shoulder belt peak load was statistically greater in the 25° condition than the 60° condition (p < 0.02). Muscle activation from the neck, upper trunk, and lower legs showed great activation. Neck muscles activation increased with the increase in seatback recline angle. Thighs, upper arms, and abdominal muscles showed small activation and no effect of conditions. Child volunteers showed decreased displacement suggesting that reclined seatbacks placed the booster-seated children in a more favorable position within the shoulder belt in a low-acceleration lateral-oblique impact, compared to nominal seatback angles. BPB type seemed to minimally influence the children's motion: the small differences found may have been due to the slight difference in heights between the two BPBs. Future research with more severe pulses is needed to better understand reclined children's motion in far-side lateral-oblique impacts.

Localizing EEG Recordings Associated With a Balance Threat During Unexpected Postural Translations in Young and Elderly Adults.

Balance perturbations are accompanied by global cortical activation that increases in magnitude when postural perturbations are unexpected, potentially due to the addition of a startle response. A specific site for best recording the response to unexpected destabilization has not been identified. We hypothesize that a single sensor located near to subcortical brainstem mechanisms could serve as a marker for the response to unpredictable postural events. Twenty healthy young (20.8 ± 2.9 yrs) and 20 healthy elder (71.7 ± 4.2 yrs) adults stood upright on a dynamic platform with eyes open. Platform translations (20 cm at 100 cm/s) were delivered in the posterior (29 trials) and anterior (5 catch trials) directions. Active EEG electrodes were located at Fz and Cz and bilaterally on the mastoids. Following platform acceleration onset, 300 ms of EEG activity from each trial was detrended, baseline-corrected, and normalized to the first trial. Average Root-Mean-Square (RMS) values across "unpredictable" and "predictable" events were computed for each channel. EEG RMS responses were significantly greater with unpredictable than predictable disturbances: Cz ( [Formula: see text]), Fz ( [Formula: see text]), and mastoid ( [Formula: see text]). EEG RMS responses were also significantly greater in elderly than young adults at Cz ( [Formula: see text]) and mastoid ( [Formula: see text]). A significant effect of sex in the responses at the mastoid sensors ( [Formula: see text]) revealed that elderly male adults were principally responsible for the age effect. These results confirm that the cortical activity resulting from an unexpected postural disturbance could be portrayed by a single sensor located over the mastoid bone in both young and elderly adults.

Neurophysiological and gait outcomes during a dual-task gait assessment in concussed adolescents.

BACKGROUND: Gait deficits are common after concussion in adolescents. However, the neurophysiological underpinnings of these gait deficiencies are currently unknown. Thus, the goal of this study was to compare spatiotemporal gait metrics, prefrontal cortical activation, and neural efficiency between concussed adolescents several weeks from injury and uninjured adolescents during a dual-task gait assessment. METHODS: Fifteen concussed (mean age[SD]: 17.4[0.6], 13 female, days since injury: 26.3[9.9]) and 17 uninjured adolescents (18.0[0.7], 10 female) completed a gait assessment with three conditions repeated thrice: single-task walking, single-task subtraction, and dual-task, which involved walking while completing a subtraction task simultaneously. Gait metrics were measured using an inertial sensor system. Prefrontal cortical activation was captured via functional near-infrared spectroscopy. Neural efficiency was calculated by relating gait metrics to prefrontal cortical activity. Differences between groups and conditions were examined, with corrections for multiple comparisons. FINDINGS: There were no significant differences in gait metrics between groups. Compared to uninjured adolescents, concussed adolescents displayed significantly greater prefrontal cortical activation during the single-task subtraction (P = 0.01) and dual-task (P = 0.01) conditions with lower neural efficiency based on cadence (P = 0.02), gait cycle duration (P = 0.03), step duration (P = 0.03), and gait speed (P = 0.04) during the dual-task condition. INTERPRETATION: Our findings suggest that several weeks after injury concussed adolescents demonstrate lower neural efficiency and display a cost to gait performance when cognitive demand is high, e.g., while multitasking, suggesting that the concussed adolescent brain is less able to compensate when attention is divided between two concurrent tasks.

The effect of a moderately reclined seat-back angle on the kinematics of the Large-Omnidirectional Child Anthropomorphic Test Device with and without a belt-positioning booster in frontal crashes.

OBJECTIVE: The effect of reclined seatbacks during frontal crashes in children seated on a belt-positioning booster (BPB) is not understood. Therefore, the aim of this study is to examine submarining in reclined child occupants with and without a BPB and with and without a simulated pre-pretensioner (PPT). We used the Large Omnidirectional Child (LODC) Anthropomorphic Test Device (ATD) seated on a production vehicle seat with and without a moderately reclined seatback angle during sled-simulated frontal vehicle crashes. METHODS: Ten sled-simulated frontal impact tests were performed (24 g peak, 80 ms duration, 56 km/h delta-V). An adjustable D-ring anchor simulated a seat integrated belt. A fixed load-limited 3-point seatbelt webbing system was used to secure the LODC to a vehicle seat and booster seat. We compared the following conditions: a) BPB vs no-BPB and b) 25° versus 45° seatback angles, c) PPT, vs no-PPT in 45° seatback condition, each test was repeated. Abdominal forces (left and right), seatbelt loads, Anterior-Superior-Illiac-Spine forces (ASIS, upper and lower, left and right), and pelvis rotation were analyzed. RESULTS: Average peak abdominal pressures were smaller in both nominal and moderate recline positions in the BPB (25°: 73.7 kPa, 45°: 82.5 kPa) compared to the no-BPB conditions (25°: 168.4 kPa, 45°: 339.1 kPa). In the 45° recline no-BPB conditions, both the peaks of the lap belt force and ASIS forces occurred early and a rapid reduction in those forces followed. This change in the lap belt and ASIS forces accompanied a rearward rotation of the pelvis. During the reduction of ASIS and lap belt forces, there was an increase in abdominal pressure suggesting that the lap belt moved upward, off the ASIS, and into the abdominal pressure sensor. There was a slight reduction in head and knee excursion with the PPT. These results suggest the presence of submarining in the 45° recline no-BPB conditions but not in the 45° recline with the BPB. CONCLUSIONS: The BPB could be beneficial when the seatback is moderately reclined. The differences during the moderate recline between the BPB and no-BPB conditions also indicate that the BPB could prevent submarining in moderately reclined seats.

A MEG compatible, interactive IR game paradigm for the study of visuomotor reach-to-target movements in young children and clinical populations: The Target-Touch Motor Task.

BACKGROUND: The conventional focus on discrete finger movements (i.e., index finger flexion or button-box key presses) has been an effective method to study neuromotor control using magnetoencephalography (MEG). However, this approach is challenging for young children and not possible for some people with physical disability. NEW METHOD: We have developed a novel, interactive MEG compatible reach-to-target task to investigate neuromotor function, specifically for use with young children. We used an infrared touch-screen frame to detect responses to targets presented using custom software. The game can be played using a conventional computer monitor or during MEG recordings via projector. We termed this game the Target-Touch Motor Task (TTMT). RESULTS: We demonstrate that the TTMT is a feasible motor task for use with young children including children with physical impairments. TTMT response-to-target trial counts are also comparable to conventional methods. Artifacts from the touch screen, while present > 100 Hz, did not affect MEG source analysis in the beta band (14-30 Hz). MEG responses during TTMT game play reveal robust cortical activity from expected areas of motor cortex as typically observed following movements of the upper limb. COMPARISON WITH EXISTING METHOD(S): The TTMT paradigm allows participation by individuals with a broad range of motor abilities on a reach-to-target' functional task rather than conventional tasks focusing on discrete finger movements. CONCLUSIONS: The TTMT is well suited for young children and successfully activates expected motor cortical areas. The TTMT opens-up new opportunities for the assessment of motor function across the lifespan, including for children with physical limitations.

Head contacts in second-row pediatric occupants when the front-seat is reclined during automated emergency braking.

Seating configurations for autonomous driving will include reclined front seated occupants, which may expose child occupants seated directly behind to head impacts even in pre-crash scenarios. This study used mathematical modelling to investigate head contact for second-row child occupants seated behind a reclined front-seat during an automatic emergency braking (AEB) scenario. Although characterized by low speed (<1 m/s), head contacts were observed for a seatbelt-restrained 10-year-old and a 6-year-old in a low-back booster when the front-seat was reclined and in an aftward track position. Future seating configurations should consider the potential for head contact by second-row child occupants during crash-avoidance scenarios.

Utility of peripheral visual cues in planning and controlling adaptive gait.

PURPOSE: To determine the relative importance to adaptive locomotion of peripheral visual cues provided by different parts of the visual field. METHODS: Twelve subjects completed obstacle crossing trials while wearing goggles that provided four visual conditions: upper visual field occlusion, lower visual field occlusion (LO), circumferential peripheral visual field occlusion (CPO), and full vision. The obstacle was either positioned as a lone structure or within a doorframe. RESULTS: Given that subjects completed the task safely without cues from the lower or peripheral visual field, this suggests that subjects used exteroceptive information provided in a feed-forward manner under these conditions. LO and CPO led to increased foot placement distance from the obstacle and to increased toe clearance over the obstacle with a reduced crossing-walking velocity. The increased variability of dependent measures under LO and CPO suggests that exproprioceptive information from the peripheral visual field is generally used to provide online control of lower limbs. The presence of the doorframe facilitated lead-foot placement under LO by providing exproprioceptive cues in the upper visual field. However, under CPO conditions, the doorframe led to a further reduction in crossing velocity and increase in trail-foot horizontal distance and lead-toe clearance, which may have been because of concerns about hitting the doorframe with the head and/or upper body. CONCLUSIONS: Our findings suggest that exteroceptive cues are provided by the central visual field and are used in a feed-forward manner to plan the gait adaptations required to safely negotiate an obstacle, whereas exproprioceptive information is provided by the peripheral visual field and used online to "fine tune" adaptive gait. The loss of the upper and lower peripheral visual fields together had a greater effect on adaptive gait compared with the loss of the lower visual field alone, likely because of the absence of lamellar flow visual cues used to control egomotion.

Age Differences in Occupant Motion during Simulated In-Vehicle Swerving Maneuvers.

BACKGROUND: With active safety and automated vehicle features becoming more available, unanticipated pre-crash vehicle maneuvers, such as evasive swerving, may become more common, and they may influence the resulting effectiveness of occupant restraints, and consequently may affect injury risks associated with crashes. Therefore, the objective of this study was to quantify the influence of age on key occupant kinematic, kinetic, and muscular responses during evasive swerving in on-road testing. METHODS: Seat belt-restrained children (10-12 years old), teens (13-17 years old), and adults (21-33 years old) experienced two evasive swerving maneuvers in a recent model sedan on a test track. Kinematics, muscle activity, and seat belt load distribution were determined and analyzed. RESULTS: Compared to teens and adults, children showed greater head and trunk motion (p < 0.03), but similar muscle activation in the into-the-belt direction of swerving. In the out-of-the-belt direction, children showed head and trunk motion more similar to teens and adults (p < 0.02), but with greater muscle activation. CONCLUSIONS: Children showed different neuromuscular control of head and trunk motion compared to older occupants. This study highlights differences in the relationship between kinematics and muscle activation across age groups, and provides new validation data for active human body models across the age range.

The effect of vehicle countermeasures and age on human volunteer kinematics during evasive swerving events.

Objective: Emergency maneuvers such as evasive swerving often precede a crash. These events are typically low-acceleration, time-extended events where the inertial forces have the potential to cause changes to the occupant's initial state (initial posture, position, muscle tension). The objective of this study was to systematically quantify the kinematics of pediatric and adult human volunteers during simulated pre-crash evasive swerving maneuvers and evaluate the effect of age and two vehicle-based countermeasures.Methods: A novel laboratory device was designed to expose subjects to non-injurious loading conditions that mimic real-world evasive swerving events. A four-cycle oscillatory lateral pulse with a maximum acceleration of 0.72 g (0.53 g for the first lateral movement in the first cycle) was applied. Forty seat belt restrained subjects across four age groups - 9-11 years (n = 10), 12-14 years (n = 10), 15-17 years (n = 10) and 18-40 years (n = 10) - were exposed to a series of test conditions (baseline, pre-pretensioned seat belt, sculpted vehicle seat with and without inflated torso bolsters) while their kinematics were captured using 3 D motion capture and muscle activity was recorded. Reaction loads were collected from the shoulder belt and footrest. Data are presented for the first cycle only.Results: Pre-pretensioning the shoulder belt before the onset of acceleration had the greatest restraining effect on the head and trunk for all age groups. In the pre-pretensioning trials, compared to baseline, subjects exhibited 34% and 33% less head excursion, into and out of the shoulder belt respectively. Similar reductions were observed with pre-pretensioning for trunk excursion (45% and 53% reductions, in and out of the belt respectively). Inflating seat torso bolsters reduced lateral kinematics relative to baseline but to a lesser extent than the pre-pretensioner (Head Out of belt: 11%; Head Into Belt: 32% and Trunk Out of Belt: 15%; Trunk Into Belt: 27%). Although there was no overall effect of age on the magnitude of lateral displacement, different age groups employed various neuromuscular strategies to control their kinematics.Conclusion: A pre-pretensioner was an effective vehicle countermeasure during evasive swerving maneuvers as it substantially reduced lateral head and trunk displacement for all age groups. Providing lateral restraint via a sculpted vehicle seat was less effective as the geometry of the torso bolsters when inflated did not provide substantial lateral support.

Characterization of the motion of booster-seated children during simulated in-vehicle precrash maneuvers.

Objective: Precrash occupant motion may affect head and trunk position and restraint performance in a subsequent crash, particularly for young children. Others have studied seat belt-restrained adult drivers and adult and adolescent passengers in precrash maneuvers. For younger children, optimal restraint includes a belt-positioning booster seat, which in precrash maneuvers may contribute in unique ways to the overall body motion. Therefore, the objective of this study was to quantify booster-seated child occupant kinematic, kinetic, and muscle responses during precrash maneuvers and characterize booster movement with respect to the overall occupant kinematics.Methods: Vehicle maneuver tests were conducted with a recent model year sedan at the Transportation Research Center Inc. (TRC, Marysville, Ohio). Three precrash vehicle maneuvers were simulated: Automated and manual emergency braking (AEB and MEB) and oscillatory swerving or slalom (SLA). Each maneuver was repeated twice for each participant. Seven 6- to 8-year-old booster-seated children participated in the study and all subjects were seated in the right rear seat. Vehicle dynamics (i.e., motion, position, and orientation) were measured with an inertial and Global Positioning System navigation system (Oxford RT 3003). Kinematic data from human volunteers were collected with an 8-camera 3D motion capture system (Optitrack Prime 13 200 Hz, NaturalPoint, Inc.). Photoreflective markers were placed on participants' head and trunk. Electromyography (EMG; Trigno EMG Wireless Delsys, Inc., 2,000 Hz) sensors were placed on bilateral muscles predicted to be most likely involved in bracing behaviors.Results: Children demonstrated greater head and trunk velocity in MEB (head 123.7 ± 13.1 cm/s, trunk 77.6 ± 14.1 cm/s) compared to AEB (head 45.31 ± 11.5 cm/s, trunk 27.1 ± 5.5 cm/s; P < .001). Participants also showed greater head motion in MEB (18.9 ± 1.4 cm) vs. AEB (15.1 ± 4.8 cm) but the differences were not statistically significant (P < .1). Overall, the booster seats themselves did not move substantially (<3 cm) in the braking maneuvers. During the SLA, however, the booster seat moved laterally up to 5 cm in several subjects, contributing substantially to peak trunk (6.5-14.0 cm) and head (9.9-21.4 cm) excursion during the maneuver. Booster-seated children also exhibited a greater activation of biceps and deltoid muscles and abdominal and middle trapezii muscles than the sternocleidomastoids during these maneuvers.Conclusions: The quantification of booster seat motion and neuromuscular control and the relationship between kinematics and muscle activation in booster-seated children in precrash maneuvers provides important data on the transition between the precrash and crash phases for this young age group and may help identify opportunities for interventions that integrate active and passive safety.

Effect of automated versus manual emergency braking on rear seat adult and pediatric occupant precrash motion.

Objective: Emergency braking can potentially generate precrash occupant motion that may influence the effectiveness of restraints in the subsequent crash, particularly for rear-seated occupants who may be less aware of the impending crash. With the advent of automated emergency braking (AEB), the mechanism by which braking is achieved is changing, potentially altering precrash occupant motion. Further, due to anatomical and biomechanical differences across ages, kinematic differences between AEB and manual emergency braking (MEB) may vary between child and adult occupants. Therefore, the objective of this study was to quantify differences in rear-seated adult and pediatric kinematics and muscle activity during AEB and MEB scenarios. Methods: Vehicle maneuvers were performed in a recent model year sedan traveling at 50 km/h. MEB (acceleration ∼1 g) was achieved by the driver pressing the brake pedal with maximum effort. AEB (acceleration ∼0.8 g) was triggered by the vehicle system. Inertial and Global Positioning System data were collected. Seventeen male participants aged 10-33 were restrained in the rear right passenger seat and experienced each maneuver twice. The subjects' kinematics were recorded with an 8-camera 3D motion capture system. Electromyography (EMG) recorded muscle activity. Head and trunk displacements, raw and normalized by seated height, and peak head and trunk velocity were compared across age and between maneuvers. Mean EMG was calculated to interpret kinematic findings. Results: Head and trunk displacement and peak velocity were greater in MEB than in AEB in both raw and normalized data (P ≤ .01). No effect of age was observed (P ≥ .21). Peak head and trunk velocities were greater in repetition 1 than in repetition 2 (P ≤ .006) in MEB but not in AEB. Sternocleidomastoid (SCM) mean EMG was greater in MEB compared to AEB, and muscle activity increased in repetition 2 in MEB. Conclusions: Across all ages, head and trunk excursions were greater in MEB than AEB, despite increased muscle activity in MEB. This observation may suggest an ineffective attempt to brace the head or a startle reflex. The increased excursion in MEB compared to AEB may be attributed to differences in the acceleration pulses between the 2 scenarios. These results suggest that AEB systems can use specific deceleration profiles that have potential to reduce occupant motion across diverse age groups compared to sudden maximum emergency braking applied manually.

Biofidelic Evaluation of the Large Omni-Directional Child Anthropomorphic Test Device in Low Speed Loading Conditions.

Motor vehicle crashes remain the leading cause of death for children. Traditionally, restraint design has focused on the crash phase of the impact with an optimally seated occupant. In order to optimize restrain design for real-world scenarios, research has recently expanded its focus to non-traditional loading conditions including pre-crash positioning and lower speed impacts. The goal of this study was to evaluate the biofidelity of the large omni-directional child (LODC) ATD in non-traditional loading conditions by comparing its response to pediatric volunteer data in low-speed sled tests. Low-speed (2-4 g, 1.9-3.0 m/s) frontal (0°), far-side oblique (60°), and far-side lateral (90º) sled tests, as well as lateral swerving (0.72 g, 0.5 Hz) tests, were conducted using the LODC. The LODC was restrained using a 3-point-belt with an electromechanical motorized seat belt retractor, or pre-pretensioner. Motion capture markers were placed on the head, torso, and belt. The LODC was compared to previously collected pediatric volunteer data as well as the HIII 10 and Q10. Significant difference between the pediatric volunteers and ATDs were identified by comparing the mean ATD response to the pediatric volunteer 95% CI. The LODC exhibited lower forward head excursion (262 mm) compared to pediatric volunteers (263 - 333 mm) in low-speed frontal sled tests (p<0.05), but was closer to the pediatric volunteers than the HIII 10 (179 mm) and Q10 (171 mm). In lateral swerving, the LODC (429 mm) exhibited greater lateral head excursion (p<0.05) compared to pediatric volunteers (115 - 171 mm). The LODC exhibited a greater reduction in kinematics compared to the pediatric volunteers in all loading conditions with a pre-pretensioner. These data provide valuable insight into the biofidelity of the LODC in non-traditional loading conditions, such as evaluating pre-crash maneuvers on occupant response.

Is lower peripheral information weighted differently as a function of step number during step climbing?

The importance of peripheral visual information during stair climbing and how peripheral visual information is weighted as a function of step number during step climbing is unclear. Previous authors postulated that the knowledge of predictable characteristics of the steps may decrease reliance on foveal vision and transfer the online visual guidance of stair climbing to peripheral vision. Hence the aim of this study was to investigate if and how the occlusion of the lower peripheral visual field influenced stair climbing and if peripheral visual information was weighted differently between steps. Ten young adult male participants ascended a 5-step staircase under 2 visual conditions: full vision (FV) and lower visual occlusion (LO). Kinematic data (100Hz) were collected. The effect of Vision and Step condition on vertical forefoot clearance was examined with a Repeated Measures 2-way ANOVA. Tukey's HSD test was used for post-hoc comparisons. A significant interaction Vision x Step and main effect of Step were found (p<=0.04): vertical forefoot clearance was greater in LO compared to FV condition only on the 1st and the 2nd steps (p<0.013) and on the last step compared to the other steps (p<0.01). These findings suggest that online peripheral visual information is more relevant when negotiating the first two steps, rather than the end of a staircase and that the steps subsequent the first few ones may require different information likely based on proprioception or working memory of the step height.

The use of the greater trochanter marker in the thigh segment model: implications for hip and knee frontal and transverse plane motion.

BACKGROUND: The greater trochanter marker is commonly used in 3-dimensional models; however, its influence on hip and knee kinematics during gait is unclear. Understanding the influence of the greater trochanter marker is important when quantifying frontal and transverse plane hip and knee kinematics, parameters which are particularly relevant to investigate in individuals with conditions such as patellofemoral pain, knee osteoarthritis, ACL injury and hip pain. The aim of this study was to evaluate the effect of including the greater trochanter in the construction of the thigh segment on hip and knee kinematics during gait. METHODS: Three-dimensional kinematics were collected in 19 healthy subjects during walking using a surface marker system. Hip and knee angles were compared across two thigh segment definitions (with and without greater trochanter) at two time points during stance: peak knee flexion (PKF) and minimum knee flexion (MinKF). RESULTS: Hip and knee angles differed in magnitude and direction in the transverse plane at both time points. In the thigh model with the greater trochanter the hip was more externally rotated than in the thigh model without the greater trochanter, (PKF -9.34°±5.21° vs 1.40°±5.22°, MinKF -5.68°±4.24° vs 5.01°±4.86°, p<0.001). In the thigh model with the greater trochanter, the knee angle was more internally rotated compared to the knee angle calculated using the thigh definition without the greater trochanter (PKF 14.67°±6.78° vs 4.33°±4.18°, MinKF 10.54°±6.71° vs -0.01°±2.69°, p<.001). Small but significant differences were detected in the sagittal and frontal plane angles at both time points (p<.001). CONCLUSION: Hip and knee kinematics differed across different segment definitions including or excluding the greater trochanter marker, especially in the transverse plane. Therefore when considering whether to include the greater trochanter in the thigh segment model when using a surface markers to calculate 3-dimensional kinematics for movement assessment, it is important to have a clear understanding of the effect of different marker sets and segment models in use.

Trunk and lower extremity segment kinematics and their relationship to pain following movement instruction during a single-leg squat in females with dynamic knee valgus and patellofemoral pain.

OBJECTIVES: To understand how instructing females with patellofemoral pain to correct dynamic knee valgus affects pelvis, femur, tibia and trunk segment kinematics. To determine if pain reduction in the corrected condition was associated with improved segment kinematics. DESIGN: Cross-sectional. METHODS: A 3D-motion capture system was used to collect multi-joint kinematics on 20 females with dynamic knee valgus and patellofemoral pain during a single-leg squat in two conditions: usual movement pattern, and corrected dynamic knee valgus. During each condition pain was assessed using a visual analog scale. Pelvis, femur, tibia and trunk kinematics in the frontal and transverse planes were compared between conditions using a paired T-test. Pearson correlation coefficients were generated between visual analog scale score and the kinematic variables in the corrected condition. RESULTS: In the corrected condition subjects had increased lateral flexion of the pelvis toward the weight-bearing limb (p<0.001), decreased femoral adduction (p=0.001) and internal rotation (p=0.01). A trend toward decreased tibial internal rotation (p=0.057) and increased trunk lateral flexion toward the weight-bearing limb (p=0.055) was also found. Lower pain levels were associated with less femoral internal rotation (p=0.04) and greater trunk lateral flexion toward the weight-bearing limb (p=0.055). CONCLUSIONS: Decreased hip adduction after instruction was comprised of motion at both the pelvis and femur. Decreased pain levels were associated with lower extremity segment kinematics moving in the direction opposite to dynamic knee valgus. These results increase our understanding of correction strategies used by females with patellofemoral pain and provide insight for rehabilitation.

Classification of lower extremity movement patterns based on visual assessment: reliability and correlation with 2-dimensional video analysis.

CONTEXT: Abnormal movement patterns have been implicated in lower extremity injury. Reliable, valid, and easily implemented assessment methods are needed to examine existing musculoskeletal disorders and investigate predictive factors for lower extremity injury. OBJECTIVE: To determine the reliability of experienced and novice testers in making visual assessments of lower extremity movement patterns and to characterize the construct validity of the visual assessments. DESIGN: Cross-sectional study. SETTING: University athletic department and research laboratory. PATIENTS OR OTHER PARTICIPANTS: Convenience sample of 30 undergraduate and graduate students who regularly participate in athletics (age = 19.3 ± 4.5 years). Testers were 2 experienced physical therapists and 1 novice postdoctoral fellow (nonclinician). MAIN OUTCOME MEASURE(S): We took videos of 30 athletes performing the single-legged squat. Three testers observed the videos on 2 occasions and classified the lower extremity movement as dynamic valgus, no change, or dynamic varus. The classification was based on the estimated change in frontal-plane projection angle (FPPA) of the knee from single-legged stance to maximum single-legged squat depth. The actual FPPA change was measured quantitatively. We used percentage agreement and weighted κ to examine tester reliability and to determine construct validity of the visual assessment. RESULTS: The κ values for intratester and intertester reliability ranged from 0.75 to 0.90, indicating substantial to excellent reliability. Percentage agreement between the visual assessment and the quantitative FPPA change category was 90%, with a κ value of 0.85. CONCLUSIONS: Visual assessments were made reliably by experienced and novice testers. Additionally, movement-pattern categories based on visual assessments were in excellent agreement with objective methods to measure FPPA change. Therefore, visual assessments can be used in the clinic to assess movement patterns associated with musculoskeletal disorders and in large epidemiologic studies to assess the association between lower extremity movement patterns and musculoskeletal injury.