An analysis of human comfort when entering and exiting the rear seat of an automobile

Identifying car ingress movement strategies before and after total knee replacement

Background: Post-operative performance of knee bearings is typically assessed in activities of daily living by means of motion capture. Biomechanical studies predominantly explore common tasks such as walking, standing and stair climbing, while overlooking equally demanding activities such as embarking a vehicle. Aims: The aim of this work is to evaluate changes in the movement habits of patients after total knee arthroplasty surgery in comparison to healthy age-matched control participants. Methods: A mock-up car was fabricated based on the architecture of a common vehicle. Ten control participants and 10 patients with severe osteoarthritis of the knee attended a single- and three-motion capture session(s), respectively. Participants were asked to enter the car and sit comfortably adopting a driving position. Three trials per session were used for the identification of movement strategies by means of hierarchical clustering. Task completion time was also measured. Results: Patients’ movement behaviour didn’t change significantly following total knee arthroplasty surgery. Control participants favoured different movement strategies compared to patients post-operatively. Group membership, height and sidedness of the affected joint were found to be non-significant in task completion time. Conclusion: This study describes an alternative movement identification technique for the analysis of the ingress movement that may be used to clinically assess knee bearings and aid in movement simulations and vehicle design.

A novel approach to predict ingress/egress discomfort based on human motion and biomechanical analysis

This study proposes an ingress/egress discomfort prediction algorithm using an in-depth biomechanical method and motion capture database. The ingress/egress motion of the subject was captured using an optical motion capture system and physically adjustable vehicle mock-up. The subjective discomfort evaluation data were also recorded at the same time. The inverse kinematics and inverse dynamics were performed to analyze captured ingress/egress motion. These procedure provide motion and joint torque information on each subject. Based on the analysis results, this study proposes the following novel features: accumulated movement of joint and sum of rectified joint torque. This study conducted a feature selection procedure to identify a relevant feature subset. Recursive feature selection and optimal feature selection methods found the most relevant feature subset with collected subjective responses. Finally, we constructed the prediction model using support vector machine. The prediction model was evaluated through prediction accuracy and statistical analysis. For comparison with the previous study, this study implemented two representative models and compare the result with those of the previous studies using the identical dataset. The effectiveness of proposed algorithm was demonstrated in comparison with previous studies.

Constitutive kinematic modes and shapes during vehicle ingress/egress

A study was undertaken to investigate the kinematics of older users of passenger vehicles during ingress/egress and to seek correlations between their movement and comfort rating assigned by the subjects to the ease of vehicle ingress and egress. A principal component analysis was performed on the subjects' kinematics to identify the underlying modes of movement employed by the subjects. It was found that a small number of modes could describe the movements of all the subjects across all of the vehicles. Within the subspace defined by the modal vectors, shapes were found which correlated to the comfort rating for ease of ingress and egress which the subjects had assigned to each of the cars. Knowledge of these shapes which correspond to good and poor ingress and egress will be useful to the designers of interiors and exteriors of passenger vehicles for the older person. It is recommended that vehicle designs for the older person should attempt to avoid body positions which require excessive ankle articulation and lumbar flexion/extension during ingress and egress.

Discomfort and muscle activation during car egress in drivers with hemiplegia following stroke

[Purpose] This study investigated and compared the discomfort experienced during car egress with the car door opened at different angles and muscle activation in drivers with hemiplegia following stroke and non-disabled drivers. [Subjects and Methods] The participants were five drivers with hemiplegia and five non-disabled drivers. The discomfort experienced during car egress was measured using the nine-point Likert scale when the door was opened wide and when it was opened 45°. Muscle activation was measured using the TeleMyo 2400T G2 electromyography system. Electromyograph electrodes were placed on the erector spinae, rectus abdominis, and rectus femoris muscles. [Results] In the non-disabled drivers, there was no significant difference in the discomforts they experienced during car egress when the door was opened wide and when it was opened 45°. However, the discomfort experienced by drivers with hemiplegia when the door was opened 45° was significantly higher than that experienced when it was opened wide. There was a significant difference in the activation of the erector spinae, but no difference in the activation of the rectus abdominis or rectus femoris muscles. [Conclusion] This study will help to understand the difficulties experienced by drivers with hemiplegia following stroke during car ingress and egress.

A 3D analysis of the joint torques developed during driver's ingress-egress motion

Providing an easy ingress-egress (I/E) movement remains a challenge for car designers. I/E has been largely studied in kinematics, but not in dynamics. This study proposes: (1) to evaluate and describe the motor torques developed in the lower limbs and lumbar joints during I/E motions and (2) to analyse the influence of the car geometry and subject anthropometry. An experiment was performed to observe 15 subjects of three anthropometrical groups getting in and out of a car mock-up simulating three different vehicle configurations. Motor torques were extracted using an inverse dynamics analysis. Both ingress and egress motions were primarily characterised by large torques. Overall, the taller a subject and the lower the seat of the vehicle were, the larger the peak torques were. Moreover, peak torques were higher for egress than ingress. These results are discussed in regard to the current knowledge on I/E ergonomics.

PRACTITIONER SUMMARY

Car ingress–egress (I/E) is an ergonomics challenge. Little is known about the physical efforts developed in this motion. Developed motor torques were experimentally assessed for three anthropometrical groups and vehicle configurations. Results obtained were discussed in regard to the current knowledge on I/E ergonomics.

An experimental investigation on the requirement of roof height and sill width for car ingress and egress

This study aimed at experimentally investigating the influence of roof height and sill width on car ingress/egress movements. The first uncomfortable (Ht1) and the lowest acceptable (Ht2) roof heights were obtained from 26 participants of three different stature groups thanks to a multi-adjustable vehicle mock-up. Both Ht1 and Ht2 were affected neither by stature nor by vehicle type. Only a difference of 45 mm between Ht1 and Ht2 was observed. Tall volunteers more flexed the trunk and neck than short persons thanks to a larger space available around the seat when the head passing under the roof. The vehicle type had almost no effect on upper body posture. The roof height only affected neck flexion. The sill width mainly imposed a lateral translation. Results demonstrated that an appropriate roof height should be determined carefully. A small change of 45 mm in roof height may lead to an unacceptable situation.

PRACTITIONER SUMMARY

The present study experimentally investigated the effects of roof height and sill width on car ingress and egress movements. Short females required almost the same roof height as tall males due to smaller space around the seat. The results would help to optimise car dimensions for improving car accessibility.

Modelling of shoulder and torso perception of effort in manual transfer tasks

The aim of the present study was to develop statistical models of perceived effort at the shoulder and torso levels associated with manual load transfer tasks. The motions were directed from a home location toward one of twenty-two target shelves distributed in the right hemisphere. A total of 2149 ratings were obtained from 31 subjects for effort perception at the selected joints, using a ten-point modified Borg scale. Regression models, developed for the perception associated with each body part, included target locations (azimuth, height and distance), posture constraints (standing or sitting), task types (one or two handed transfer conditions), and demographic and anthropometric measures (stature, body weight, gender, and age) as parameters. The models provide a prediction of effort perception with adjusted r-square coefficients of 0.41 and 0.50 for the shoulder and torso, respectively. The results indicate that space and posture interact in a complex way to affect the rating of perceived effort, and are in agreement with the hypothesis that the 'sense of effort' is primarily associated with the efference copy of the descending motor command. Since a level of effort is not associated with a unique pattern of motor command, it is proposed that effort perception is likely to result from a summation of the components of the motor command. The models can be applied to optimize the spatial organization of the work environment in an attempt to reduce the risk of musculoskeletal injury.

Kinematics of head-trunk movements while entering and exiting a car

The study of free and natural accessibility movements for a medium-sized car was carried out, recording the motor performances of ten participants by means of a motion analysis system. The experimental protocol used passive markers to implement a two-segment biomechanical model for the analysis of the head-trunk complex. The kinematic variables quantify the motor patterns, and showed specific features that can be related to the individual anthropometric characteristics and to the car geometry differences: tall participants used a neck flexion and a leftwards bending of the head, while short participants extended the neck and bent the head to the right. The different seat positions (short participants move forwards the seat) along with the principal need to avoid any body interference with the car, can explain the observed strategies. From the wider analysis of the movements in relation to the vehicle's features and to the anthropometric size of the participants, this approach could lead to an extension of the design criteria for those structural components of the car which have been demonstrated to significantly influence the human-machine interaction.