Biodynamics and Discomfort of the Human Body in a Seated Posture with a Large Backrest Inclination Angle

Large-reclined seating has emerged as a favored configuration in the luxury transport sector. While the static advantages are evident, the effect of this posture on dynamic comfort is not clear. This study investigated the objective biodynamics and subjective discomfort of the human body sitting in a large-reclined posture (58° from the vertical) under single axis vertical and lateral vibration excitations. The transmissibility of the human–seat system and apparent mass of the human body were measured respectively. The results revealed a critical transition between static and dynamic comfort: while the 58° posture offers superior static relaxation, dynamic discomfort dominates the overall perception when the excitation intensity exceeds a threshold of 0.249 m/s2 r.m.s. Objective measurements indicated that dynamic comfort degradation in large-reclined postures is primarily driven by altered inherent biodynamic characteristics. These findings highlight that future luxury vehicle seating must incorporate targeted dynamic isolation to compensate for posture-induced comfort degradation and ensure premium ride quality.