Car seat impact on driver’s sitting behavior and perceived discomfort during prolonged real driving on varied road types

Prolonged driving under real conditions can entail discomfort linked to driving posture, seat design features, and road properties like whole-body vibrations (WBV). This study evaluated the effect of three different seats (S1 = soft; S2 = firm; S3 = soft with suspension system) on driver’s sitting behavior and perceived discomfort on different road types in real driving conditions. Twenty-one participants drove the same 195 km itinerary alternating highway, city, country, and mountain segments. Throughout the driving sessions, Contact Pressure (CP), Contact Surface (CS), Seat Pressure Distribution Percentage (SPD%) and Repositioning Movements (RM) were recorded via two pressure mats installed on seat cushion and backrest. Moreover every 20 minutes, participants rated their whole-body and local discomfort. While the same increase in whole-body discomfort with driving time was observed for all three seats, S3 limited local perceived discomfort, especially in buttocks, thighs, neck, and upper back. The pressure profiles of the three seats were similar for CP, CS and RM on the backrest but differed on the seat cushion. The soft seats (S1 & S3) showed better pressure distribution, with lower SPD% than the firm seat (S2). All three showed highest CP and CS under the thighs. Road type also affected both CP and CS of all three seats, with significant differences appearing between early city, highway and country segments. In the light of these results, automotive manufacturers could enhance seat design for reduced driver discomfort by combining a soft seat cushion to reduce pressure peaks, a firm backrest to support the trunk, and a suspension system to minimize vibrations.

Vibration Attenuation Via Mean of Lower Limb Muscles Occurs During Whole Body Vibrations And Differs Across Frequencies And Postures

Lower limb muscles actively contribute to maintain body posture but also act to attenuate soft tissues oscillations that occur during everyday life. This elicited activity can be exploited as a mean of neuromuscular training or rehabilitation. In this study, Whole Body Vibrations (WBV) at different frequencies were delivered to healthy subjects while holding static postures to test the transient muscles mechanical responses. Twenty-five participants underwent WBV at 15, 20, 25 and 30 Hz while holding either a static ‘hack squat’ or ‘fore feet’ posture. Soft tissue accelerations and surface electromyography (sEMG) were recorded from Gastrocnemius Lateralis (GL), Soleus (SOL) and Tibialis Anterior (TA) muscles. Estimated displacement at muscle bellies revealed a resonant pattern, different across frequencies and postures (p<.001). Specifically, a peak in the displacement was measured after the onset of the stimulation, followed by a drop and a further plateau (only after few seconds after the peak) suggesting a delayed neuromuscular activation. Although oscillation dampening was correlated to an increased muscular activity, only specific WBV settings were promoting a significant muscle contraction. For example, SOL and GL induced activation was maximal for subject in forefeet and while exposed to higher frequencies (p<.05). The non-immediate response of leg muscles to a vibratory stimulation confirms the tonic nature of the vibration induced muscle contraction (the tonic vibration reflex) and its strong influence on postural tonic muscles (GL and SOL). This may have significant impact on training or rehabilitation protocols aiming towards postural and balance improvement or recovery.

Health efficacy of electrically operated automated massage on muscle properties, peripheral circulation, and physio-psychological variables: a narrative review

Manual massage, commonly used by healthy individuals for well-being, is an ancient practice requiring the intervention of a trained and experienced physiotherapist. On the other hand, automated massage is carried out by machines or modalities without or with minimal control of a human operator. In the present review, we provide a literature analysis to gather the effects of automated massage on muscle properties, peripheral circulation and psychophysiological variables as reported through psychometric and neurophysiological evaluations of each modality ranging from massage beds and whole-body vibrations to robotic massage. A computerized search was performed in Google Scholar, PubMed, and ResearchGate using selected key search terms, and the relevant data were extracted. The findings of this review indicate that for vibration massage, whole-body vibration exposure with relatively lower frequency and magnitude can be safely and effectively used to induce improvements in peripheral circulation. As for massage chair and mechanical bed massage, while most studies report on positive changes, the lack of strong clinical evidence renders these findings largely inconclusive. As for robotic massage, we discuss whether technological advances and collaborative robots might reconcile active and passive modes of action control during a massage and offer new massage perspectives through a stochastic sensorimotor user experience. This transition faculty, from one mode of control to the other, might definitely represent an innovative conceptual approach in terms of human–machine interactions.

Frequency dependence of vertical whole-body vibration perception - is your car rattling or humming?

Humans perceive whole-body vibration in many daily life situations. Often they are exposed to whole-body vibration in combination with acoustic events. Sound and vibration usually stems from the same source, for example concerts or travelling in vehicles, such as automobile, aircrafts, or ships. While we can describe acoustic stimuli using psychoacoustic descriptors such as loudness or timbre, the description human perception of whole body vibration frequently has been reduced to comfort or quality in the past. Unlike loudness or timbre, comfort and quality are dependent on the overall context. Especially in vehicles expectations might differ lot between different vehicle classes. Previous studies have evaluated a large range of suitable descriptors for whole-body vibrations that are independent of context. They suggest that certain descriptors are driven to a large extend by the frequency content of the vibration. This study systematically investigates the influence of frequency content on the perception of whole-body vibration varying frequency content and intensity of the vibrations. The results verify the frequency dependence of specific descriptors and identify the respective frequency ranges.

Perception thresholds for whole-body vibrations on an airplane seat

The comfort during a flight on an aircraft is important for passengers. Like many other physical factors, vibrations of the airplane may negatively affect comfort. To understand the impact of vibration on comfort, it is important to know in which way the vibrations transmitted through the seat affects the perception of whole-body-vibrations. In this study, perception thresholds for vertical sinusoidal whole-body vibrations with frequencies between 20 Hz and 75 Hz were determined on a vibration platform with a typical economy class aircraft seat bench. Acceleration levels were recorded with accelerometers placed at the right rear seat rail and inside a seat cushion between the seat surface and the participant. The results show a distinct frequency dependency of the detection thresholds when measured at the seat rail. When taking the difference between the two measurement positions into account and describing the thresholds by the acceleration levels at the seat cushion, the determined perception thresholds are nearly frequency independent up to 50 Hz. This finding is in good agreement with literature data suggesting that the specific experimental setup does not play a big role in this frequency range. Differences above 50 Hz might be explained by the additional armrests in the present study.

NUMERICAL ANALYSIS OF HUMAN SPINE DURING WHOLE BODY VIBRATION

Vibrations are oscillatory movements of the mechanical system, in which displaments of points are small compared to the dimensions of the system. Exposure to whole body vibrations reduces the comfort of passengers in the vehicles, causing stress, fatigue and discomfort. Vibrations can affect the lumbar spine, the gastrointestinal system, the peripheral veins and the vestibular system. In this study, one male subject was exposed to WBV while driving on the highway at a speed of 80 km/h. The movements recorded on the vehicle seat were transferred to a 3D spine model. Numerical results of Von Misses stress and deformation were presented.