  Vibration transmission is essential in the design of comfortable vehicle
seats but knowledge is lacking on 3D trunk and head motion and the role of seat
back and posture. We hypothesized that head motion is reduced when participants
upper back is unsupported, as this stimulates active postural control. We
developed an experimental methodology to evaluate 3D vibration transmission
from compliant seats to the human body. Wide-band (0.1-12 Hz) motion stimuli
were applied in fore-aft, lateral and vertical direction to evaluate the
translational and rotational body response in pelvis, trunk and head. A
standard car seat was equipped with a configurable and compliant back support
to test 3 support heights and 3 sitting postures (erect, slouched, and
preferred) where we also tested head down looking at a smartphone. Seat back
support height and sitting posture substantially affected vibration
transmission and affected low-frequency responses in particular for body
segment rotation. According to our hypothesis a low support height proved
beneficial in reducing head motion. Relevance to industry: Our methodology
effectively evaluates 3D wide-band vibration transmission from compliant seats
to the human body. The lowest back support height reduced head motion but was
perceived as least comfortable. This calls for seat designs which support but
do not so much constrain the upper back. The head down posture enlarged head
motion, pleading for computer system integration allowing heads up postures in
future automated cars. The biomechanical data will serve to validate human
models supporting the design of comfortable (automated) vehicles.
