Southard Stephanie A, Mirka Gary A
The Ergonomics Laboratory, Department of Industrial Engineering, Box 7906, North Carolina State University, Raleigh, NC 27695-7906, USA.
Appl Ergon. 2007 Sep;38(5):541-7. doi: 10.1016/j.apergo.2006.08.007. Epub 2006 Nov 16.
Much of the research on backpack design has been focused on spinal loading/biomechanics while the wearer is in a neutral/upright trunk posture, such as those employed by outdoor enthusiasts and schoolchildren. This research has led to some important harness design improvements that reduce trunk muscle exertions, fatigue and improve overall comfort. There are number of occupations, however, wherein workers wear back-mounted packs/devices (e.g. air tanks) while working in non-neutral trunk postures. The objective of the current study was to evaluate the effects of these non-neutral postures on biomechanical loading and then reconsider the backpack system design recommendations. Fifteen participants were asked to support a 18.2 kg load on their back while assuming static forward flexed postures of the torso (15 degrees , 30 degrees , 45 degrees , and 60 degrees of sagittal bend). The mass on the back was attached to the participant through two different harness mechanisms: a basic harness design (as seen on college student backpacks) and a more advanced design containing lateral stiffness rods and a weight-bearing hip belt (as seen on backpacks for hikers). While performing these static, posture maintenance tasks, the activation levels of the bilateral trapezius, erector spinae, and rectus abdominis were collected. Participants also provided subjective ratings of comfort. The results showed that there was a significant interaction between harness type and forward flexion angle for the trapezius and the erector spinae muscles. The normalized EMG for the trapezius muscles showed a 14% and 11% reduction in muscle activity at 15 degrees and 30 degrees , respectively, with the advanced design but these positive effects of the advanced design were not found at the greater flexion angles. Likewise the erector spinae muscles showed a 24% and 14% reduction in muscle activity at 15 degrees and 30 degrees , respectively, with the advanced design harness but these effects of the advanced design were not found at the greater forward flexion angles. The level of forward flexion angle affected the rectus abdominis muscle activity, but neither the harness type main effect nor the interaction of harness type and forward flexion angle was significant. The subjective survey results agreed with the EMG results and showed the advanced design harness was generally more comfortable with respect to the shoulder and low back areas. Collectively, the subjective and objective results show a significant improvement with the advanced harness system but also note an interesting interaction with degree of sagittal flexion, indicating a diminished effectiveness of the design improvements at forward flexed postures. Design criteria for harness systems in these forward flexed postures are discussed.
许多关于背包设计的研究都集中在穿戴者处于中立/直立躯干姿势时的脊柱负荷/生物力学方面，比如户外爱好者和学童所采用的姿势。这项研究带来了一些重要的背带设计改进，减少了躯干肌肉的用力、疲劳，并提高了整体舒适度。然而，有许多职业，工人在非中立躯干姿势下工作时会背着后置背包/设备（如空气罐）。本研究的目的是评估这些非中立姿势对生物力学负荷的影响，然后重新考虑背包系统的设计建议。15名参与者被要求在背部承受18.2千克的负荷，同时保持躯干的静态前屈姿势（矢状面弯曲15度、30度、45度和60度）。背部的重物通过两种不同的背带机制连接到参与者身上：一种是基本的背带设计（如大学生背包上所见），另一种是更先进的设计，包含侧向刚度杆和承重腰带（如徒步旅行者背包上所见）。在执行这些静态的姿势维持任务时，收集双侧斜方肌、竖脊肌和腹直肌的激活水平。参与者还提供了舒适度的主观评分。结果表明，斜方肌和竖脊肌的背带类型和前屈角度之间存在显著交互作用。斜方肌的标准化肌电图显示，采用先进设计时，在15度和30度时肌肉活动分别减少了14%和11%，但在更大的前屈角度时，先进设计的这些积极效果并未出现。同样，竖脊肌在采用先进设计背带时，在15度和30度时肌肉活动分别减少了24%和14%，但在更大的前屈角度时，先进设计的这些效果并未出现。前屈角度水平影响腹直肌的肌肉活动，但背带类型的主效应以及背带类型和前屈角度的交互作用均不显著。主观调查结果与肌电图结果一致，表明先进设计背带在肩部和下背部区域通常更舒适。总体而言，主观和客观结果表明先进背带系统有显著改进，但也注意到与矢状面屈曲程度存在有趣的交互作用，表明在向前屈曲姿势下设计改进的效果减弱。讨论了这些向前屈曲姿势下背带系统的设计标准。
