To facilitate application of the information provided in this guide, a model warning information system will be developed in this chapter with reference to 15 different body dimensions. This system assists the user in rapidly identifying the relevant specific properties of a body dimension and the resulting conclusions for its application in standardization and design work.
The warning information system used below for classification of the individual body dimensions comprises four different warning levels:
Body dimensions assigned to this warning level can be applied during the design process without limitations. Possible biological changes caused by ageing, environmental influences (nutrition, health) or exercise can be ignored. Body dimensions assigned to Warning Level 0 are the dimensions of the individual long bones and of the skull, such as the upper arm length, the head length and the head breadth. These skeleton-based dimensions remain virtually unchanged following completion of the growth phase.
Body dimensions assigned to this warning level are subject to changes during the ageing process, owing to the diminished ability to maintain the spine straight and the diminished elasticity of the intervertebral discs. This results in body dimensions, including the trunk length, being reduced with increasing age. Dimensions affected include the body height, eye height, trunk length and trunk length + head height. Accordingly, body dimensions dependent upon the spine should be reduced by approximately 20 mm in the context of design work for the 50+ age group, owing to the age-related changes to the spine (Greil et al. 2008).
Body dimensions assigned to Warning Level 2 are subject to frequent variability owing to environmental influences, such as the nutritional conditions. These dimensions change rapidly within a population. This can be explained by general fluctuations in weight and also by the natural increase in weight in more advanced age. A large proportion of the dimensions of Warning Level 2 are circumferential dimensions, such as the chest girth, waist girth, thigh girth or lower leg girth. However, this category also includes breadth and depth dimensions the landmarks of which are also determined on the skin surface in the form of soft tissue dimensions.
Owing to the growing proportion of overweight persons in the population, the percentile values of circumferential and breadth dimensions in older collections of data must be regarded as now being too low to reflect the current situation. Accordingly, an allowance should be added to the upper percentile values (see Up-to-dateness of anthropometric data). In Germany for example, an allowance of up to 50 mm should be added to the body breadth sitting, in order for the ergonomics to take account of the growing group of obese persons.
During the performance of movements or as a result of allowances for clothing, body dimensions that are assigned to Warning Level 3 differ in practice substantially from the body dimensions stated in standards, which were obtained by standardized measurement methods.
These body dimensions particularly include the group of functional dimensions, and also dimensions the measurement paths of which also include joint points, such as the trunk length + head height, the trunk length, the projective arm length and the knee height. Body dimensions to which an allowance must be added for clothing and footwear are also assigned to Warning Level 3.
Allowances of 35 mm for footwear, 5 mm for light clothing, 8-10 mm for heavy clothing and 10-35 mm for headgear are added in the Handbuch der Ergonomie to the respective dimensions. Data influenced by the physiology of the spine, i.e. data that are measured in a comfortable body posture, differ from the values measured in the standard position by approximately 1-1.5%.
EN ISO 3411 governing earthmoving machinery specifies the observance of allowances of 25 mm for the height of shoes and boots, and of 50 mm for protective helmets. A reduction of 15 mm in the values for the body height and overhead reach is recommended for the movement envelope with the body in a non-erect posture, i.e. in the normal, relaxed body posture. Reduction of the values by 25 mm is recommended for the "height sitting" and "eye height sitting".
