Passive stiffness changes in the lumbar spine and effect of gender during prolonged simulated driving

Gender differences in lumbar and pelvic posture have been reported previously in prolonged sitting, both in an office chair and automobile seat. To date, it is not known whether these postural exposures during prolonged driving affect the passive lumbar spine flexion stiffness. The purpose of this study was to examine time-varying responses of passive lumbar spine stiffness, lumbar spine and pelvic postures during a 2 h simulated driving trial. Secondary goals investigated the influence of gender on lumbar spine stiffness, discomfort scores and seat pressure profiles. Twenty (10 males, 10 females) subjects were recruited to complete a 2 h simulated driving task. Passive lumbar range of motion was measured on a customized frictionless jig before, halfway through and at the end of 2 h. During driving there was a time-varying difference in the lumbar flexion angles adopted by the gender groups. A significant interaction (p = 0.0458) was found for gender and time with women being found to sit significantly different than males in the second hour of driving exhibiting greater maximum lumbar flexion (60.0% ROM (±1.27) than men 50.0% ROM (±1.5). Both men and women demonstrated similar passive stiffness changes characterized by an initial increase in transitional zone stiffness after 1 h (+0.1 Nm/degree for males and +0.3 Nm/degree for females, p = 0.2372). Over 2 h of driving there was a non-significant trend of genders to respond differently to the seated exposure. Specifically transitional zone stiffness was found to increase in males (0.86 (SD 0.31) to 0.92 (SD 0.31) Nm/degree) and decrease in females (0.81 (SD0.88) to 0.73 (SD 0.52) Nm/degree) (p = 0.1178). Differences in lumbar posture and passive stiffness over 2 h of simulated driving were demonstrated between genders in this study.Relevance to industryGender specific ergonomic interventions should be investigated for the automobile seat. Additionally, the changes in passive stiffness induced by prolonged seated exposures could introduce altered low back kinematics in activities performed after a long car ride. Lifting scenarios such as luggage unloading or parcel delivery are common activities immediately after driving. The altered stiffness of the lumbar spine in these activities could have potential ergonomics and injury related implications for both the general population and professional drivers.

► Gender differences in lumbar posture and stiffness found in prolonged driving.
► Females had more lumbar flexion and less stiffness than men after 2 h.
► Stiffness changes can impact back kinematics of activities after long car rides.
► Ergonomic interventions for automobile seat should consider these findings.