Beeman Stephanie M, Kemper Andrew R, Duma Stefan M
a Virginia Tech, Department of Biomedical Engineering and Mechanics, Center for Injury Biomechanics , Blacksburg , VA.
Traffic Inj Prev. 2016 Sep;17 Suppl 1:141-9. doi: 10.1080/15389588.2016.1205190.
The objective of this study was to quantify the effects of active muscles (e.g. conscious bracing, resting tone, and reflex response) and acceleration severity on the neck forces and moments generated during low-speed frontal sled tests with adult male human volunteers and post mortem human surrogates (PMHSs).
A total of 24 frontal sled tests were analyzed including male volunteers of approximately 50th percentile height and weight (n = 5) and PMHSs (n = 2). The tests were performed at two acceleration severities: low (∼2.5 g, Δv ≈ 5 kph) and medium (∼5.0 g, Δv ≈ 10 kph). Each volunteer was exposed to two impulses at each severity, one relaxed and one braced, while each PMHS was exposed to one impulse at each severity. Linear acceleration and angular velocity of the head were measured at a sampling rate of 20kHz, then filtered using SAE Channel Frequency Class 180 and 60, respectively, and transformed to the head center of gravity (CG). The location of the head CG, external auditory meatus, and occipital condyle (OC) were approximated using pretest photos and literature values. Neck forces (Fx and Fz) and sagittal plane moments (My) were calculated at the OC by applying the equations of dynamic equilibrium to the head.
Peak Fx, Fz, and My increased significantly with increasing acceleration severity (p < 0.1). Minimal differences were observed between the magnitudes of the peak forces and moments for each subject type. Qualitatively, differences in the timing of peak neck forces and moments and the overall shape of the time histories were evident. Maximum Fx, Fz, and My occurred earliest in the event for the braced volunteers and latest for the PMHSs. However, these differences were not supported statistically for the volunteers (p > 0.05). The timing of neck loading was visibly augmented by the increased stiffness of the volunteer necks as a result of muscle activation. Although differences were observed between the volunteer muscle conditions, the volunteer subsets were more similar to each other than the PMHSs.
This study examined the effects of active muscles, in the form of conscious and reflexive muscle activity, on the biomechanical response of occupants in low-speed frontal sled tests. Although active bracing did not result in significantly different peak neck loads or moments, the timing of these peak values were affected by muscle condition. The findings of this study provide insight to the kinetics experienced during low-speed sled tests and are important to consider when refining and validating computational models and ATDs used to assess injury risk in automotive collisions.
本研究的目的是量化主动肌肉（如自觉支撑、静息肌张力和反射反应）以及加速度严重程度对成年男性人类志愿者和人体尸体替代物（PMHS）在低速正面雪橇试验中产生的颈部力和力矩的影响。
共分析了24次正面雪橇试验，包括身高和体重约为第50百分位数的男性志愿者（n = 5）和PMHS（n = 2）。试验在两种加速度严重程度下进行：低（约2.5g，Δv≈5公里/小时）和中（约5.0g，Δv≈10公里/小时）。每位志愿者在每种严重程度下接受两次脉冲，一次放松，一次支撑，而每个PMHS在每种严重程度下接受一次脉冲。以20kHz的采样率测量头部的线性加速度和角速度，然后分别使用SAE通道频率类别180和60进行滤波，并转换到头部重心（CG）。使用试验前照片和文献值近似估算头部CG、外耳道和枕髁（OC）的位置。通过将动态平衡方程应用于头部，在OC处计算颈部力（Fx和Fz）和矢状面力矩（My）。
随着加速度严重程度的增加，峰值Fx、Fz和My显著增加（p < 0.1）。每种受试者类型的峰值力和力矩大小之间观察到最小差异。定性地说，峰值颈部力和力矩的时间以及时间历程的整体形状存在明显差异。对于支撑的志愿者，最大Fx、Fz和My在事件中出现最早，而对于PMHS出现最晚。然而，对于志愿者来说，这些差异在统计学上没有得到支持（p > 0.05）。由于肌肉激活，志愿者颈部刚度增加明显增加了颈部加载时间。尽管在志愿者肌肉状态之间观察到差异，但志愿者亚组彼此之间比PMHS更相似。
本研究检验了有意识和反射性肌肉活动形式的主动肌肉对低速正面雪橇试验中乘员生物力学反应的影响。尽管主动支撑并未导致峰值颈部负荷或力矩有显著差异，但这些峰值的时间受肌肉状态影响。本研究结果为低速雪橇试验中所经历的动力学提供了见解，在改进和验证用于评估汽车碰撞中损伤风险的计算模型和ATD时，这些结果很重要，值得考虑。
