Effect of Class I–III obesity on driver seat belt fit

Approximately 40% of the U.S. adult population are obese. An issue associated with this trend is proper seat belt fit for obese occupants. This study extends previous research, in which few individuals with high BMI (> 40 kg/m2) were included, by examining the relationship between participant and belt factors on belt fit for drivers with Class I-III obesity. Posture and belt fit of 52 men and women with BMI from 31 to 59 kg/m2 (median 38 kg/m2) were measured in a laboratory vehicle mockup. Five seat belt configurations were achieved by manipulating the belt anchorage locations. Body and belt landmark locations were recorded using a three-dimensional coordinate measuring machine. Higher BMI was associated with a lap belt position further forward and higher relative to the pelvis. On average, the lap belt was positioned an additional 32 mm forward and 13 mm above the ASIS with each increasing level of obesity classification. Sex had a small effect after accounting for BMI and stature. The mean fore-aft location of the lap belt was 24 mm more forward for men vs. women and 12 mm higher for women vs. men at the same stature and BMI. On average, women used 50 mm more belt webbing in the lap and 92 mm more in the shoulder vs. men. The results suggest that increasing levels of obesity class effectively introduces slack in the seat belt system by routing the belt further away from the skeleton. Because the belt is designed to engage the pelvis during a frontal crash, belt placements that are higher and further forward may increase injury risk by allowing excursions or submarining. Unique to this cohort, sex had an important effect on belt fit measures after taking into account stature and BMI. The participant and belt factors considered explained only about 40% of the variance in belt fit. The remaining variance may be due to preference or exogenous body shape effects. Further research is needed to assess methods for enhanced seat belt fit for people with obesity, including addressing sex differences in belt routing.美国成年人口中约有40%处于肥胖状态。伴随这一流行趋势的一项关键问题，是肥胖乘员的安全带贴合适配难题。本研究针对既往研究中高身体质量指数（BMI）>40 kg/m²的受试者占比极少的局限，通过探究受试者与安全带相关因素对I至III级肥胖驾驶员安全带贴合度的影响，拓展了相关研究的边界。本研究在实验室车辆模拟装置中，对52名BMI介于31至59 kg/m²（中位数为38 kg/m²）的男女受试者的身体姿态与安全带贴合度进行了测量。通过调整安全带锚点位置，共设置了五种安全带配置方案。采用三维坐标测量机记录了人体与安全带的标志点位置。研究发现，BMI越高，腰部安全带（lap belt）相对于骨盆的位置越靠前且越高；每提升一级肥胖分级，腰部安全带平均会额外前移32 mm，且相较于髂前上棘（ASIS，Anterior Superior Iliac Spine）的高度额外升高13 mm。在控制BMI与身高的影响后，性别对贴合度的影响相对较小：在身高与BMI相同的前提下，男性的腰部安全带平均前后位置较女性靠前24 mm，而女性的安全带高度则较男性高12 mm。平均而言，相较于男性，女性的腰部安全带区域多使用了50 mm的织带，肩部安全带区域则多使用了92 mm的织带。研究结果表明，肥胖分级的提升会使安全带偏离骨骼更远，从而在安全带系统中引入额外的松余量。由于安全带的设计目标是在正面碰撞时贴合骨盆，位置偏高且靠前的安全带可能会使乘员发生位移或潜滑，进而提升损伤风险。与既往研究不同的是，在本次研究的受试者队列中，在控制身高与BMI的影响后，性别对安全带贴合度指标具有显著影响。本次研究纳入的受试者与安全带相关因素，仅能解释约40%的安全带贴合度变异量，剩余的变异量可能源于受试者的佩戴偏好或外源性体貌特征影响。未来仍需开展相关研究，以评估提升肥胖人群安全带贴合度的可行方案，其中包括解决安全带路径选择中的性别差异问题。