Four-degree-of-freedom (4-DOF) human-chair coupling models are constructed to characterize the different contact modes between the head, chest back, waist back and backrest. The seat-to-head transfer ratio (STHT) is used as an evaluation metric for vibration reduction effectiveness. The simulated vibration reduction ratio of the model is close to the experimental results, which proves the validity of the model. The peak STHT is obviously reduced (P < 0.05, T-test) with seat-backrest support. The experiments show that supporting the head ( a 1 , P < 0.05, Wilcoxon matched-pairs signed ranks) has the best vibration reduction effect (21%), supporting the chest back ( a 2 , P < 0.05) has a reduced effect (11%), and supporting the waist back ( a 3 , P < 0.05) has the weakest effect (4%). When the upper torso is in full contact with the backrest, the peak STHT curve and resonance frequency are positively correlated with the contact stiffness of the seat surface and negatively correlated with the contact damping. In order to reduce the seat-to-head transfer ratio, the lowest STHT peak and lowest total energy judgments were proposed as the selection methods for the selection of the contact stiffness and damping of the backrest in two environments (periodic and non-periodic excitation), respectively.

Prior investigations have been primarily conducted in a laboratory to examine the effects of the smartphone use on the neck and head positions, whether these results are applicable to actual conditions is still unknown. This field survey thus analyzed the neck flexion (NF), head flexion (HF), gaze angle (GA), and viewing distance (VD) of smartphone users in public areas in Taipei, Taiwan. Six hundred smartphone users (300 men and 300 women) were photographed sagittally in standing, supported sitting, or unsupported sitting postures while using a smartphone. Results showed that women had significantly less NF and HF and shorter VDs than male users. Regardless of gender, higher NF was observed for standing than for sitting. Women had similar NF and HF while sitting supported and unsupported, but both were significantly lower than those while standing. By contrast, male users had higher NF and HF during unsupported sitting than during supported sitting. The NF (45°-50°) was much greater than the recommended maximum safe NF of 15°. Women may be at higher risk of visual strain because of shorter VD.

Expiratory droplets cause high infection risk to nearby passengers via airborne route.
We built a two-row four-seat setup to simulate a public transport cabin. A cough generator and a nebulizer were used to simulate the cough and talk processes respectively. Exposure and infection risk of nearby passengers was studied. The effect of gasper jet and backrest on risk mitigation was investigated.
For the activity of coughing, the front passenger has much higher infection risk, which was around four times of that of other passengers, because of the concentration surge in the inhalation zone. For talking, the nearby passengers have similar infection risk because nearby passengers were all exposed to concentration surges with similar peak value. Gasper jet of the infected passenger and higher backrest can extinguish or reduce the concentration surge of front passengers and reduce the infection risk due to coughing and talking droplets.
The passengers near the infected passenger have very high infection risk. The overhead gasper and a higher backrest can reduce the exposure and mitigate the risk of infection. It is believed that the control measures to protect nearby passengers are urgently needed in public transport cabins.

BACKGROUND: Autonomous vehicles can be classified on a scale of automation from 0 to 5, where level 0 corresponds to vehicles that have no automation to level 5 where the vehicle is fully autonomous and it is not possible for the human occupant to take control. At level 2, the driver needs to retain attention as they are in control of at least some systems. Level 3-4 vehicles are capable of full control but the human occupant might be required to, or desire to, intervene in some circumstances. This means that there could be extended periods of time where the driver is relaxed, but other periods of time when they need to drive.
OBJECTIVE: The seat must therefore be designed to be comfortable in at least two different types of use case.
METHODS: This driving simulator study compares the comfort experienced in a seat from a production hybrid vehicle whilst being used in a manual driving mode and in autonomous mode for a range of postures.
RESULTS: It highlights how discomfort is worse for cases where the posture is non-optimal for the task. It also investigates the design of head and neckrests to mitigate neck discomfort, and shows that a well-designed neckrest is beneficial for drivers in autonomous mode.

Musculoskeletal sitting discomfort, specifically caused by long-term sitting, is primarily triggered by physiological fatigue on the human body due to its own weight. Passive seat designs can produce inadequate surface pressure zones on the body resulting in high musculoskeletal stress leading to physical discomfort. However, as proposed in this work, this can be alleviated by decentralizing the occupant\'s weight with an automatic morphing lumbar seat design. The morphing seat design presented in this paper adjusts in real-time, the seat\'s surface curvature to decentralize the pressure distribution. The seat system consists of a custom-made pressure sensor mat embedded within the backrest cushion and two pneumatic actuators located in the lumbar area. The purpose of this seat design is to produce a change in the backrest surface curvature so that such change creates a pressure distribution closely resembling a reference distribution. Said reference distribution is derived in this work based on the concept of the Ideal Pressure Distribution. The effectiveness of the discomfort reduction due to the decentralization of the backrest load is evaluated using an objective discomfort metric known as Seat Pan Distribution percentage applied only to the backrest, peak pressure areas and contact area. Preliminary performance tests of the seat system demonstrate the successful decentralization of the passenger\'s pressure distribution. The evaluation of the discomfort reduction is observed via the lowering in the objective discomfort metric and peak pressure areas while simultaneously increasing the contact area between the passenger and seat.

Spinal deformities are common in people who require the use of a wheelchair for mobility as a result of spinal cord injuries and other disabilities. Sitting positions vary between individuals with disabilities who use wheelchairs and individuals without disabilities. In individuals with spinal cord injury, spinal deformities can result in the development of back contours that deviate from the shape of standard rigid back support shells. The purpose of this study was to distinguish and classify various back contours of wheelchair users by utilizing digital anatomic scanning technology in order to inform the future development of back supports that would enhance postural support for those with spinal deformities. The three dimensional (3D) locations of bony landmarks were digitized when participants were in position, using a mechanical wand linked to the FastScan(tm) system commonly used to measure surface contours. Raw FastScan(tm) data were transformed according to bony landmarks. A total of 129 individuals participated in this study. A wide range of back contours were identified and categorized. Although participant characteristics (e.g., gender, diagnosis) were similar amongst the contour groups; no one characteristic explained the contours. Participants who were seated in a forward lean position had a higher amount of pelvic obliquity compared to those seated in an upright position; however, participants\' back contour was not correlated with pelvic obliquity. In conclusion, an array of different back shapes were classified in our cohort through 3D laser scanning technology. The methods and technology applied in this study could be replicated in future studies to categorize ranges of back shapes in larger populations of people with spinal cord injuries. Preliminary evidence indicates that customized postural support may be warranted to optimize positioning and posture when a standard rigid shell does not align with contours of a person\'s back. To optimize positioning, a range of contoured rigid backrests as well as height and angle adjustability are likely needed.

[Purpose] The purpose of this study was to investigate the effects of the thickness of a wheelchair backrest provided for support and comfort on upper arm and trunk muscle load during wheelchair propulsion by using accelerometers. [Subjects and Methods] The Fourteen healthy participants were enrolled in this study. The study compared effects of three backrest conditions including no pad, a 3-cm-thick lumbar pad, and a 6-cm-thick lumbar pad. The instruments used for measurement were used two accelerometers. The participants were asked to propel their wheelchairs, which had been equipped with two accelerometers, 30 times. [Results] The intensity of muscle movement with the 3-cm-thick lumbar pad was significantly lower than the intensities with no lumbar pad and the 6-cm-thick lumbar pad. The muscle intensity did not differ significantly between the no pad and 6-cm-thick lumbar pad conditions. [Conclusion] An appropriately thick backrest has good effects on upper arm and trunk muscles during wheelchair propulsion. In the future, we must consider the appropriate backrest thickness for providing wheelchair users with a comfortable wheelchair.

Backrests influence the comfort of seated people. With 21 subjects sitting with three backrest heights (no backrest, short backrest, high backrest) discomfort caused by lateral, roll, and fully roll-compensated lateral oscillation was investigated at frequencies between 0.25 and 1.0 Hz. With lateral oscillation, the short backrest reduced discomfort at frequencies less than 0.63 Hz and the high backrest reduced discomfort at frequencies less than 1.0 Hz. With roll oscillation, the high backrest reduced discomfort at frequencies less than 0.63 Hz, but increased discomfort at 1.0 Hz. With fully roll-compensated lateral oscillation, the short backrest reduced discomfort at 0.4 Hz and the high backrest reduced discomfort at 0.5 and 0.63 Hz. As predicted by current standards, a backrest can increase discomfort caused by high frequencies of vibration. However, a backrest can reduce discomfort caused by low frequencies, with the benefit depending on the frequency and direction of oscillation and backrest height.

OBJECTIVE: This study investigated the effects of an acupoint-stimulating lumbar backrest on pain and disability in office workers who suffering from low back pain (LBP) as well as the preference influence on pain and disability.
METHODS: Sixty-four participants were randomly assigned to two groups: one with no intervention (n=32) and another with 1 month of backrest use (n=32). An additional group (n=37) who wished to try 1 month of acupressure backrest were recruited to indicate the preference effect. Pain and disability were two key outcomes.
RESULTS: Significant differences between control and randomized acupressure backrest groups were found at 2 week period for disability and at 4 weeks for pain after the backrest use. Also, significant differences were found in both groups for 3 month period with an increase of the treatment effect on pain and disability. Both control and randomized acupressure backrest groups showed greater improvement in pain and disability scores which were more than the minimal clinically important change (30% improvement for both outcomes). No significant difference was found for pain and disability between the randomized and preferred backrest groups.
CONCLUSIONS: These findings suggested 1-month of acupressure backrest use could improve LBP conditions. Preference was not a powerful moderator to the significant treatment effect.

OBJECTIVE: The goal of this study was thus to determine if people with different types of wheelchair backrests on their personal wheelchairs reported different levels of comfort as measured by the Tool for Assessing Wheelchair disComfort (TAWC).
METHODS: Participants were between 18 and 80 years of age and were manual wheelchair users. The TAWC was used to assess the participants\' wheelchair seating discomfort levels with the wheelchair and seating systems.
RESULTS: We surveyed 131 wheelchair users to assess the comfort of their backrests on their personal wheelchairs and found a trend suggesting that rigid backrests are were less comfortable as compared with sling backrests. This finding was statistically significant in a subgroup of participants with tetraplegia.
CONCLUSIONS: Although many clinicians expect rigid backrests to be more comfortable because they may provide more support, the higher discomfort ratings among rigid backrest users with tetraplegia may be due to sub-optimal shape, fit, adjustment or user preferences. Implications for Rehabilitation Development of a measure for long-term seating discomfort is needed. Design and development of better rigid backrests that are functional but provide adequate comfort are in need.