Hendriks H M, Spoor C W, de Jong A M, Goossens R H M
Erasmus MC University Medical Center Rotterdam, Department of Biomedical Physics and Technology, Dr. Molewaterplein 50, 3015 GE Rotterdam, The Netherlands.
Ergonomics. 2006 Dec 15;49(15):1611-26. doi: 10.1080/00140130600899161.
Observational studies of sitting have shown that, during spontaneous sitting, people adopt a variety of postures. Various researchers have formulated theories to explain why people adopt their sitting postures. Branton (1969) hypothesized that there is continual need for postural stability while sitting. Dempster (1955) stated that additional stability could be obtained through temporarily closing chains of body segments, or, in other words, through decreasing the number of degrees of freedom of the body. The present study elaborates on Dempster's theory. The aim of this study was to determine the influence of the degrees of freedom of the body on postural stability in sitting postures. For 21 different sitting postures, the total number of degrees of freedom was determined. Postural sway, a measure for postural stability, was determined using a 3D motion and position measurement system with ten healthy subjects. This study shows that the mean path length at the level of the second thoracic vertebra (PL0.05), a measure derived from postural sway, increases significantly (p < 0.0001) with an increase of the number of degrees of freedom of the body (DoFB). Closer examination of the data showed that a model taking into account only the degrees of freedom of the lumbar and thoracic spine and pelvis seems to be a better predictor of postural sway than the total number of degrees of freedom of the body.
关于坐姿的观察性研究表明，在自然坐姿状态下，人们会采用多种姿势。不同的研究人员提出了各种理论来解释人们为何会采取特定的坐姿。布兰顿（1969年）推测，坐着时持续需要保持姿势稳定。登普斯特（1955年）指出，通过暂时闭合身体各部分的链式结构，或者换句话说，通过减少身体的自由度数量，可以获得额外的稳定性。本研究进一步阐述了登普斯特的理论。本研究的目的是确定身体自由度对坐姿姿势稳定性的影响。对于21种不同的坐姿，确定了自由度的总数。使用三维运动和位置测量系统对10名健康受试者进行姿势摆动测量，姿势摆动是姿势稳定性的一个指标。本研究表明，从姿势摆动得出的一个指标——第二胸椎水平的平均路径长度（PL0.05），随着身体自由度数量（DoFB）的增加而显著增加（p < 0.0001）。对数据的进一步分析表明，一个仅考虑腰椎、胸椎和骨盆自由度的模型，似乎比身体自由度总数更能预测姿势摆动。
