Seat Position Research Articles

Effectiveness of a Text Message Intervention Promoting Seat Belt Use Among Young Adults

Approximately 1 in 10 adults do not always wear a seat belt, with the lowest use rates reported among young adults. To determine the efficacy of a 6-week automated behavioral text message program promoting seat belt use compared with an attention control. This parallel, 2-group, single-blind, individually randomized clinical trial included a convenience sample of patients recruited from 4 emergency departments in 2 cities in Pennsylvania from December 2019 to September 2021, with follow-ups at 6 and 12 weeks after randomization. Patients in stable condition aged 18 to 25 years who, in standardized screening, reported driving or being a passenger in a car without always using a seat belt in the past 2 weeks were eligible for recruitment. Participants who completed a 2-week trial run-in phase were randomly assigned 1:1 to the intervention or the assessment control. Data were analyzed from October 2019 to January 2020. The intervention group received Safe Vehicle Engagement (SAVE), a 6-week automated interactive text message program, including weekly seat belt use queries with feedback and goal support to promote consistent use of a seat belt. The control group received identical weekly seat belt use queries but no additional feedback. The primary outcome was the proportion of young adults reporting always wearing a seat belt over the past 2 weeks, collected at 6 weeks (after a 2-week run-in) via web-based self-assessments and analyzed under intent-to-treat models using multiple imputation procedures. Sensitivity analyses included complete-case analyses of ordered categorical outcomes by vehicle seat position. Secondary outcomes included seatbelt use at 12 weeks and select cognitive constructs related to seat belt use. A total of 218 participants (mean [SD] age, 21.5 [2.1] years; 139 [63.8%] women) were randomized, with 110 randomized to SAVE and 108 randomized to the control group. A total of 158 individuals (72.4%) were included in the 6-week follow-up. The rate of always using a seat belt over the past 2 weeks at the 6-week follow-up was 41.3% (95% CI, 30.6%-52.0%) among SAVE participants and 20.0% (95% CI, 10.6%-29.3%) among control participants (odds ratio [OR], 2.8; 95% CI, 1.4-5.8; P = .005). A total of 140 individuals (64.2%) participated in the 12-week follow-up. At 12 weeks, the rate of always using a seat belt over the past 2-weeks was 42.8% (95% CI, 31.2%-54.2%) among SAVE participants and 30.7% (95% CI, 19.6%-41.6%) among control participants (OR, 1.7; 95% CI, 0.9-3.4; P = .13). When examining ordered categories of seat belt use by seat position, there were significantly greater odds of wearing a seat belt at 6 and 12 weeks among SAVE participants vs control participants (eg, 6 weeks for driver: OR, 5.2; 95% CI, 2.6-10.5; 6 weeks for front passenger: OR, 4.3; 95% CI, 2.2-8.2; 6 weeks for back passenger: OR, 4.3; 95% CI, 2.2-8.2). In this randomized clinical trial, an interactive text message intervention was more effective at promoting seat belt use among targeted young adults than an attention control at 6 weeks. There was no significant difference between groups in always wearing a seat belt at 12 weeks. These findings, if replicated in a larger sample, suggest a scalable approach to improve seat belt use. ClinicalTrials.gov Identifier: NCT03833713.

Effects of restraint parameters using PIPER 6y in reclined seating during frontal impact

Objective This study explores possible challenges for child occupants in reclined seating positions, applying current protection systems. Using PIPER 6 y in frontal impacts, the aim was to investigate the effect of restraint parameters in reclined seating positions, in addition to an upright position, varying booster design, shoulder belt outlet, and pretensioner activation. Method Eighteen full frontal impacts were simulated using the PIPER 6 y human body model restrained on a booster in a front passenger seat. The type of booster, pretensioner activation and shoulder belt outlet were varied with the vehicle seat in ‘upright position’ (25°) and ‘reclined position’ (40°). Three booster principles were used: booster seat (BoosterA), booster cushion (BoosterB) and representing properties of a vehicle built-in booster cushion (BoosterC). The two shoulder belt outlets include ‘nominal D-ring’ and ‘rearward D-ring´. Results Overall, activation of the pretensioner reduced the overall body displacement as well as the head and neck response in both seating positions. Submarining occurred only in the case of BoosterB in ‘reclined position’ without pretensioner. Some differences were observed for the lap belt interaction with pelvis in the non-submarining simulations. Greater pelvis displacement was observed in ‘reclined position’ as compared to ‘upright position’. In both seating positions, greatest pelvis displacement was observed for BoosterB, due to relatively more forward initial lap belt position. While both provided favorable initial lap belt to pelvis contact, BoosterC offered more efficient lap belt restraint than BoosterA, since the lap belt remained lower on the pelvis and the vertical movement of the pelvis was more limited compared to BoosterA. When in ‘reclined position’, the ‘rearward D-ring’ position enabled earlier coupling of the torso due to initial shoulder belt to shoulder contact, resulting in lower head and neck responses as well as shorter head displacement compared to ‘nominal D-ring’ Conclusions Submarining can be addressed in reclined seating positions using current booster design in combination with a seatbelt pretensioner. Lap belt routing was influenced by booster design and reclined seating, affecting the overall kinematics and responses of the PIPER 6 y. This study highlights the importance of including the whole context of child occupant protection when investigating reclined seating, such as the interaction and compatibility of booster, vehicle seat and seatbelt.

The prevalence of redundant nerve roots in standing positional MRI decreases by half in supine and almost to zero in flexed seated position: a retrospective cross-sectional cohort study

PurposeThis retrospective cross-sectional cohort study investigated the influence of posture on lordosis (LL), length of the spinal canal (LSC), anteroposterior diameter (APD L1-L5), dural cross-sectional area (DCSA) of the lumbar spinal canal, and the prevalence of redundant nerve roots (RNR) using positional magnetic resonance imaging (MRI) (0.6 T).MethodsSixty-eight patients with single-level degenerative central lumbar spinal stenosis (cLSS) presenting with RNR in the standing position (STA) were also investigated in supine (SUP) or neutral seated (SIT) and flexed seated (FLEX) positions. Additionally, 45 patients complaining of back pain and without MRI evidence of LSS were evaluated. Statistical significance was set at p < 0.05.ResultsControls (A) and patients with cLSS (B) were comparable in terms of mean age (p = 0.88) and sex (p = 0.22). The progressive transition from STA to FLEX led to a comparable decrease in LL (p = 0.97), an increase in LSC (p = 0.80), and an increase in APD L1-L5 (p = 0.78). The APD of the stenotic level increased disproportionally between the different postures, up to 67% in FLEX compared to 29% in adjacent non-stenotic levels (p < 0.001). Therefore, the prevalence of RNR decreased to 49, 26, and 4% in SUP, SIT, and FLEX, respectively.ConclusionThe prevalence of RNR in standing position was underestimated by half in supine position. Body postures modified LL, LSC, and APD similarly in patients and controls. Stenotic levels compensated for insufficient intraspinal volume with a disproportionate enlargement when switching from the STA to FLEX.

Computational Assessment of Positional Sensitivity to Injury in Spacecraft Occupants

Spacecraft occupants are susceptible to injury from sudden loads, such as those experienced during landing. Most injury biomechanics investigations assume perfect seated posture and consistent seated position. However, this assumption is unrealistic, as offsets from these presumed postures and placements are likely during impacts. In this computational study, the Global Human Body Model Consortium’s simplified 5thpercentile female and 50th and 95th-percentile male anthropometric models were seated and restrained in three positions: nominal, (“perfect” posture and placement); and 10 millimeters and 25.4 millimeters forward of the seatback. Biodynamic responses to simulations involving vertical accelerations were analyzed for positional sensitivity. The 5th-percentile female was most susceptible to neck injury due to compressive forces. In 50th and 95th-percentile males, upper spinal intervertebral forces were positively correlated to seated position (increasing 13% for 25.4mm forward offset). Analysis of head excursions and knee splay data indicates potential whiplash and the need for conformal seating, respectively.

Impact of Seat Material on Comfort, Preference and Performance During Computer-Based Tasks over a Prolonged Bout of Sitting

Prolonged sitting time is associated with negative health outcomes, including physical discomfort. Chair design affects seat posture, micro-movement, and pressure distribution, which impacts the user experience. This study investigated the impact of mesh versus foam material, on comfort, preference, and subjective performance. Two chairs were used over a three-hour bout of sitting on two different days. Analysis showed no significant difference in pain, comfort, discomfort, or fatigue between chairs, but pain increased in both chairs during the last hour of sitting. The foam chair felt more supportive than the mesh chair at the end of the test period, while more participants preferred the mesh seat material overall. The overall results indicate that there was not a substantial difference in user experience during a long bout of sitting in chairs of foam or mesh material.

Evaluating lower body driving posture regarding gas pedal control and emergency braking: A pilot study

Lower body posture influences driving comfort and safety. The posture recommendations from the literature, however, are often based on preferred postures and can be inconsistent due to differences in the experimental setups. Furthermore, the ranges of preferred postures focusing on sitting comfort are often wide and, therefore, difficult to use for occupant packaging in the automotive industry. To cope with these issues, we developed a task-oriented approach to evaluate the lower body driving posture. We predefined 12 seating positions (4 knee angles × 3 seating heights) and measured the physical strain, discomfort perception, and task performance of gas pedal control and emergency braking. Results of the 11 participants showed that seating closer to the front with a 110° knee angle caused more foot dorsiflexion for gas pedal control and increased the right leg's shin muscle activity and discomfort; seating further back with a 145° knee angle decreased emergency braking performance. In conclusion, our new approach is feasible for objectively and effectively evaluating lower body driving posture. Relevance to industryThe approach of this study can provide a new perspective on the driving posture assessment. The findings can be utilized to optimize the occupant packaging process in the automotive industry.

Protection challenges in seat positions with large rearward adjustment in frontal collisions: An approach using stochastic human body model simulations

Novel seat positions enabled by self-driving cars have been investigated in various studies in recent years. However, there is little research on the effect of increased rearward seat adjustments. To predict challenges associated with the possibility to move the seat further backwards in the car than currently possible as driver, appropriate methods have to be defined. A detailed human body model, a THUMS v4.1 in particular, tissue-based injury risk evaluation methods, a generic vehicle interior and a Latin hypercube design of experiments taking the variability of real-world crashes into account was established. In a first step, 200 simulations at current representative seat positions and a driving occupant posture were performed. The results were then compared to field data from an accident database to evaluate the accuracy of the method. The predictions exceeded the injury risks for the abdomen, head, and upper extremities, while underestimating the risk for thoracic and lower extremity injuries. A good match was observed for injuries of the neck and spine. In a second step, the 200 simulations were run again, but with the seat adjusted rearwards significantly. In this seat configuration, with the exception of the head and the upper extremities, increased injury risks were predicted for all body regions. The highest increases affected the lower extremities (+28%)—predominantly pelvic fractures—and the neck (+9%). In addition, (partial) submarining occurred in almost 50% of cases with the rearward adjusted seat—as opposed to none in the conventional seat position. The established method could be used in future studies to design safety measures addressing these identified potential safety risks.

Load-limiting in the lap belt reduces injury risks associated with new seating positions

The two objectives are to demonstrate technical feasibility for an advanced 3-point seatbelt system incorporating double lap belt pre-tensioning and load-limiting and to evaluate its injury risk reduction relative to that of a 3-point seatbelt without double lap belt load-limiting. Frontal sled tests were conducted at 50 km/h with a Hybrid III 50-percentile male in upright and reclined with the seat in a rearward position. The advanced 3-point seatbelt system satisfied all requirements and all injury risk metrics (from Euro NCAP and additional ones associated with the new seating positions) were reduced. In particular, the risk for head-to-thigh contact was substantially reduced. Therefore, the advanced 3-point seatbelt system is technically feasible and conveys substantial benefits. More research is needed to investigate the risk of submarining and sliding off the seat, using a wider range of occupant surrogates and more severe crash pulses.

Local dynamic stability of the trunk after prolonged seating with axial load

Fatigue from prolonged seating with an axial load on the trunk may impair neuromuscular control and spine stability which may elevate risk of low back pain (LBP) for dynamic tasks following seating. The objective of this study was to assess local dynamic trunk stability using the maximum Lyapunov exponent (λMAX) with corresponding coactivation patterns to understand possible effects from prolonged seating. An increase in λMAX would indicate decreased stability. Twenty participants (10 male, 10 female) performed a controlled, cyclic sagittal flexion task at 40 cycles per minute before and after three hours of seating in a simulated helicopter-seating environment with a weighted vest. A statistically significant decrease was seen in λMAX (bits/s) (Pre-Test = 0.654 ± 0.172; Post-Test = 0.829 ± 0.268, p = 0.002), trunk cumulative coactivation index (unitless/s) (Pre-Test = 1.71 ± 0.97; Post-Test = 1.59 ± 0.96, p = 0.0095), and abdominal activation (normalized) (Pre-Test = 0.46 ± 0.17, Post-Test = 0.41 ± 0.18, p = 0.0146) post-seating exposure. Trunk extension was reduced (∼4°, p = 0.0004) during the post-seating cyclic test with slight corresponding increases in flexion. This study provides evidence of potential effects of fatigue from prolonged seating to neuromuscular control, which may have implications for occupations requiring highly dynamic tasks after prolonged seated postures. Future studies would repeat the tests with dynamic environments (i.e., vibration), test the cyclic flexion protocols with different seating interventions, and continue to test the approach to develop a tool to assess back impairment or intervention effectiveness.

Effects of vertical vibration on sitting comfort in civil aviation during the cruising flight

This paper investigated the effects of vertical vibration on sitting comfort in civil aviation, with particular attention to high-frequency components (i.e. 30‒100 Hz). We generated 24 vibration stimuli at four positions (i.e. the co-pilot, front, middle, and rear seat positions) in the aircraft cabin, with magnitudes ranging from 0.05 to 2 ms−2 r.m.s. and durations of 10 s. Twenty-four subjects (12 males and 12 females) judged the vibration discomfort using a category-ratio method. We found a significant effect of high-frequency vibration on comfort: vibration stimuli at the middle and rear seats contained more energy at high frequencies and caused significantly greater discomfort than those at the co-pilot and the front seats. However, this effect became less significant with increasing magnitudes of vibration stimuli. The discomfort predicting models provided more accurate results by amplifying weighting factors for high-frequency vibration than those using standardised weightings (i.e. W b and W k weightings). Practitioner summary: The severity of high-frequency vibration for sitting comfort was usually underestimated. We investigated vibration discomfort at various seat positions in an aircraft cabin. Vibration at the middle and rear seats contained more high-frequency components and caused more discomfort. This work provided accurate predicting models of discomfort using the modified weighting.

Optimization of Seating Position and Stimulation Pattern in Functional Electrical Stimulation Cycling: Simulation Study.

Two significant challenges facing functional electrical stimulation (FES) cycling are the low power output and early onset of muscle fatigue, mainly due to the non-physiological and superficial recruitment of motor units and weakness of the antagonistic muscles. Thus optimization of the cycling biomechanical properties and stimulation pattern to achieve maximum output power with minimum applied electrical stimulus is of great importance. To find the optimal seating position and stimulation pattern, the previous works either ignored the muscle's force-velocity and force-length properties or employed complicated muscle models which was a massive barrier to clinical experiments. In this work, an easy-to-use and precise muscle model in conjunction with Jacobian-based torque transfer functions were adopted to determine the optimal seating position, trunk angle, crank arm length, and stimulation intervals. Furthermore, the impact of muscle force-velocity factor in finding the optimal seating position and stimulation intervals was investigated. The simulation models showed the trivial effect of the force-velocity factor on the resulting optimal seating position of six healthy simulated subjects. This method can enhance the FES-cycling performance and shorten the time-consuming process of muscle model identification for optimization purposes.

The effect of seating recline on sleep quality, comfort and pressure distribution in moving autonomous vehicles

The revolution of technologically advanced vehicles with a high level of automation involves a profound transformation. The focus of most research in this area has been on the use of travel time for different use cases. Sleeping is one of the most time-consuming activities in everyone's life; therefore, this has been described as one of the most desired use cases for fully automated vehicles. In order to identify the best conditions to allow sleep and improve sleep quality while travelling in such vehicles, two studies were performed: a sleep study and a pressure distribution study, the results of which are included in this document. The focus of both studies was on two seat positions: reclined (60° backrest recline) and flat (87° backrest recline). In the sleep study, forty participants had the opportunity to sleep during a 90-min drive in order to evaluate long-term comfort and subjective sleep quantity and quality. Although both positions resulted in generally similar results in terms of sleep and comfort, some significant differences were identified. Karolinska Sleepiness Scale results showed that sleepiness increased in the reclined position, whereas it decreased in the flat position. Moreover, the self-reported parameter Wake After Sleep Onset was higher in the reclined position. In the pressure distribution study, it was possible to identify specific seat prototype limitations indicating inadequate support, which was related to discomfort detected during the sleep study. As a conclusion, the comparison between the reclined and flat positions showed indications that, in moving fully automated vehicles, the flat seat position is the most comfortable and effective for sleeping.

Analysis of 6YO pediatric human body model kinematics and kinetics to determine submarining across naturalistic seating postures

Objectives The aim of this study was to analyze the kinematics and kinetics of a naturalistically seated 6-year-old (6YO) pediatric human body model and evaluate the metrics described by earlier studies for pediatric ATDs to indicate whether different postures and booster seats were more associated with submarining than others in a frontal impact. Methods The PIPER 6YO pediatric human body model was restrained on a lowback (LBB) and a highback (HBB) booster child restraint seat (CRS) in four naturalistic seating postures: leaning-forward, leaning-inboard, leaning-outboard, and a pre-submarining posture, and a baseline reference seating position as per the FMVSS No. 213 protocol. A 2012 mid-size sedan finite element (FE) model was used as the vehicle environment. A standard 3-point lap-shoulder belt system was modeled to restrain the child and the CRS in the left-rear vehicle seat. Additionally, a No-CRS condition was modeled in a reference posture and pre-submarining posture in which the occupant’s legs bent over the edge of the rear seat. 12 conditions were simulated in LS-DYNA R10.1.0, and kinematics and kinetics were compared to metrics as per prior literature: 1) maximum femur displacement and pelvis rotation, 2) maximum knee-head excursion and maximum change in torso angle, 3) lap belt trajectory relative to pelvis’s coordinate frame. Results The pre-submarining posture on the HBB depicted submarining in all metrics except for the lap belt trajectory. Only the pre-submarining posture in No-CRS depicted submarining through analysis of all metrics. For this pre-submarining No-CRS condition, the mid-abdominal compression was approximately 5 times greater than the average of the mid abdominal compression depths of all other cases and maximum abdominal pressure was at least 22.9 kPa higher than the rest of the conditions. Conclusions The results of this study suggest that metrics used to assess submarining for 6YO pediatric occupants in frontal impacts may need to be updated so that they are more accurate for both simulated and physical studies. In addition, the results of this study could be used to design booster seats that discourage postures that could lead to an increased likelihood of submarining-like characteristics in a frontal crash impact.

Is Internal Rotation Measurement of the Hip Useful for Ruling in Cam or Pincer Morphology in Asymptomatic Males? A Diagnostic Accuracy Study.

Cam and pincer morphologies are associated with limited internal rotation. However, the routine clinical examination for hip rotation has limited reliability. A more standardized method of measuring hip rotation might increase test-retest and interobserver reliability and might be useful as a screening test to detect different hip morphologies without the need for imaging. We developed an examination chair to standardize the measurement of internal hip rotation, which improved interobserver reliability. However, the diagnostic test accuracy for this test is unknown. Is a standardized method of determining internal hip rotation using an examination chair useful in detecting cam and pincer morphology with MRI as a reference standard? A diagnostic test accuracy study was conducted in a sample of asymptomatic males. Using an examination chair with a standardized seated position, internal rotation was measured in 1080 men aged 18 to 21 years who had been conscripted for the Swiss army. The chair prevents compensatory movement by stabilizing the pelvis and the thighs with belts. The force to produce the internal rotation was standardized with a pulley system. Previous results showed that the measurements with the examination chair are similar to clinical assessment but with higher interobserver agreement. A random sample of 430 asymptomatic males was invited to undergo hip MRI. Of those, 244 White European males responded to the invitation and had a mean age of 20 ± 0.7 years and a mean internal rotation of the hip of 33° ± 8.5°. Using MRI as the reference standard, 69% (169 of 244) had a normal hip, 24% (59 of 244) a definite cam morphology (Grades 2 and 3), 3% (8 of 244) an increased acetabular depth, and 3% (8 of 244) a combination of both. One experienced radiologist graded cam morphology as follows: 0 = normal, 1 = mild, 2 = moderate, and 3 = severe. Pincer morphology was defined by increased acetabular depth (≤ 3 mm distance between the center of the femoral neck and the line connecting the anterior and posterior acetabular rims). The intraobserver agreement was substantial (weighted κ of 0.65). A receiver operating characteristic (ROC) curve was fitted, and sensitivity, specificity, and likelihood ratios were estimated for different internal rotation cutoffs. For cam morphology, the area under the ROC curve was 0.75 (95% CI 0.67 to 0.82). Internal hip rotation of less than 20° yielded a positive likelihood ratio of 9.57 (sensitivity 0.13, specificity 0.99), and a value of 40° or more resulted in a negative likelihood ratio of 0.36 (sensitivity 0.93, specificity 0.20). The area under the curve for detecting the combination of cam and pincer morphologies was 0.87 (95% CI 0.74 to 1.0). A cutoff of 20° yielded a positive likelihood ratio of 9.03 (sensitivity 0.33, specificity 0.96). This examination chair showed moderate-to-good diagnostic value to rule in hip cam morphology in White European males. However, at the extremes of the 95% confidence intervals, diagnostic performance would be poor. Nonetheless, we believe this test can contribute to identifying cam morphologies, and we hope that future, larger studies-ideally in more diverse patient populations-will seek to validate this to arrive at more precise estimates of the diagnostic performance of this test. Level III, diagnostic study.

Reducing Lumbar Spine Vertebra Fracture Risk With an Adaptive Seat Track Load Limiter

In future fully automated vehicles, sleeping or resting will be desirable during a drive. While a horizontal position currently appears infeasible, a relaxed seating position with a reclined seatback and an inclined seat pan which enables a safe, comfortable position for sleeping or resting is possible. However, the inclined seat pan increases the forces and moments acting on the lumbar spine of the occupant and thereby the risk of lumbar vertebra fractures in a frontal crash. An energy management system integrated into the longitudinal seat adjustment (a seat track load limiter: STLL) that can reduce this risk should be investigated. When evaluating the injury reduction potential of a new restraint system such as a STLL it is important to include variations in both occupant size and crash severity. Otherwise, there is a risk of sub-optimizing, that is, the restraint system is only working for a limited number of situations. The restraint systems addressing these variations are normally referred to as adaptive restraint systems. The first objective of the study is to develop an activation strategy (adaptive release time of the STLL) for different crash severities and occupant sizes, making full use of the available stroke distance without bottoming out the STLL. The second objective is to evaluate the potential of the adaptive STLL to reduce the risk of lumbar vertebra fractures by comparing it to 1) a fixed seat and 2) a passive version of the STLL. Simulated frontal impacts were performed with two male SAFER human body models (HBMs) as occupant surrogates: mid-sized (80 kg and 1.8 m) and large (130 kg and 1.9 m). Three crash pulse severity levels were evaluated: low (40 km/h), medium (50 km/h), and high (56 km/h) impact speeds. The fracture risk was evaluated for the five lumbar vertebrae (L1–L5) in three different seat conditions: 1) a seat fixed to the sled, 2) a passive STLL that moves when a given force is exceeded, and 3) an adaptive STLL which moves at a time that depends on the occupant mass and crash pulse severity. The risk for lumbar vertebra fracture increased with crash pulse severity, while HBM size had no effect on risk. For all conditions, the passive STLL reduced injury risks compared to the fixed seat, and the adaptive STLL reduced risk even further.

A naturalistic study of passenger seating position, posture, and restraint use in second-row seats

Objective The objective of the current study was to increase scientific understanding of rear-seat passenger seating position, postures, CRS use, and belt use through a naturalistic study. A secondary objective was to compare data from vehicles used in ride-hailing with data from other vehicles. Method Video cameras were installed in the passenger cabins of the vehicles of 75 drivers near the center of the windshield. The video data were downloaded after the vehicles were operated by their owners for two weeks. Video frames were sampled from near the ends and in the middle of each trip, and at five-minute intervals in trips longer than 15 min. A total of 7,323 frames with second-row passengers were manually coded. Results A total of 444 unique second-row passengers were identified in video frames from 1,188 trips taken in 65 of the 75 vehicles in the study. Two of the vehicles that were driven for commercial ride-hailing during the study period accounted for 199 (45%) of the passengers. Considering multiple passengers in some trips, a total of 1,899 passenger-trips were identified. For passengers not using child restraint systems (CRS), the belt use rate was 65% in the non-ride-hailing vehicles versus 32% among passengers in the ride-hailing vehicles. No CRS use was observed in the ride-hailing vehicles. Among children using backless boosters, the shoulder belt was lateral to the clavicle or under the arm in 26% of frames. Among belted passengers not using CRS, the belt was lateral to the clavicle or on the neck about 6% of the time. Belted passengers not using CRS were observed leaning to the left or right about 27% of the time, with leaning away from the shoulder belt more common than leaning into the belt. Conclusions This study is the first to report seating position, posture, and belt fit observations for a large naturalistic sample of second-row passengers that includes adult occupants. The data suggest that low rear seat belt use rates remain a concern, particularly in ride-hailing vehicles. Non-nominal belt placement and posture may also be common in second-row seating positions.

Reliability and Validity of the ActivForce Digital Dynamometer in Assessing Shoulder Muscle Force across Different User Experience Levels.

BackgroundCurrently available hand-held dynamometers (HHD) offer a more objective and reliable assessment of muscle force production as compared to a manual muscle test (MMT). Yet, their clinical utility is limited due to high cost. The ActivForce (AF) digital dynamometer is a new low-cost HHD with unknown psychometric properties, and its utilization may benefit clinical practice.Hypothesis/PurposeThis study aimed to determine the AF intra- and inter-tester reliabilities, standard error of measurement (SEM), minimal detectable change (MDC), and criterion validity for assessing shoulder isometric force as compared to the microFET2 (MF2) across testers with different experiences.DesignDescriptive observational study.MethodsA convenience sample of 29 healthy adults were assessed twice by each of three testers (two experienced clinicians and a novice PT student) on shoulder external rotation (ER), internal rotation (IR), and forward elevation (FE) using both the AF and MF2 devices. Tester, HHD, and shoulder motion assignment orders were randomized. All testing was performed in a standardized seated position. ER and IR were tested with the shoulder fully adducted. FE was tested at 45° at the scapular plane. All testing and rest periods between testers and tested motions were standardized and monitored via a stopwatch.ResultsBoth devices had high intra- [ ER (.95-.98), IR (.97 - .99), FE (.96 - .99)] and inter-tester [ ER (.85-.96), IR (.95 - .97), FE (.88 - .95)] intraclass correlation coefficient (ICC) with comparable intra- (1.68-1.80) and inter-tester (2.36-2.98) SEM, and intra- (4.64-4.97) and inter-tester (6.50-8.24) MDC values across all motions. Tester experience did not affect these values. High (.89-.93) statistically significant Pearson correlations were found between HHDs for all shoulder motions.ConclusionBoth the AF and MF2 HHDs were found to have high reliability levels across all shoulder motions regardless of tester clinical experience. The AF was also found to be valid for measuring shoulder isometric force production compared to the criterion standard device, the MF2. Its low-cost and electronic accessibility features may promote better compliance for clinicians using dynamometry to objectively assess and store muscle force data in a cost-effective manner.Level of Evidence3

Percentage of U.S. General Population Accommodated by Commercial Airline Seats

The number of seats per airplane has increased over the years, leading to a decrease in seat width and legroom. Using the HFES Multivariate Accommodation Testing Tool, the percentage of the general population accommodated in a static seated posture was calculated with respect to two important design dimensions of airline seats, seat width and legroom. Results from this article can inform seat manufacturers and airlines on how to design seats that physically accommodate the largest number of passengers. This paper does not address passenger safety and comfort, which are complex, multi-factor issues that extend beyond physical accommodation.

Child Restraint Use and Seating Position of Child Passengers in Motor Vehicles and Their Correlations: Application of a Random-Effects Bivariate Probit Model

Motor vehicle crashes are a leading cause of death and injury for children aged under 8 years. In the U.S.A., while some states are showing increases in the proportion of child restraint device use, only around half of child passengers aged from 4 to 7 years are being properly restrained. This study was undertaken to identify the factors contributing to the proper child restraint use and child passenger’s seating position through the direct observation surveys of more than 10,000 child passengers in 2015 and 2018 in Michigan. A bivariate probit model with random effects was developed to identify simultaneously the contributing factors for the proper restraint use and seating position of child passengers, accounting for the unobserved heterogeneity in the data. The bivariate framework is able to account for the correlation of the two dependent variables in the study. The results show that the two dependent variables are positively correlated, and this correlation is strongly significant. The key factors simultaneously influencing proper child restraint use and appropriate seating position of the child passenger include the age of the child, the number of child passengers in the vehicle, driver belt use, driver gender, age, and race, vehicle type, stratum, weather, and the time of the day and week. However, factors such as county-specific population, income, and education, and the type of location did not have any significant association with either child restraint use or the seating position of the child passenger.

On-Machine Measurements for Aircraft Gearbox Machining Process Assisted by Adaptive Neuro-Fuzzy Inference System

This paper deals with the development of dimensional control technology for the production of accessory drive train (ADT) gearbox housing, according to the closed door technology approach. The work presents the methodology of the final inspection of bearing seat position deviation by replacing the coordinate measuring machines (CMMs) with a computerized numerical control (CNC) machine and adaptive neuro-fuzzy inference system. The results of the work indicated that correct solutions were obtained. In addition, the technological process of manufacturing is fully automated and performed entirely on the production line.