Working Posture Assessment

The TACOS (Time-Based Assessment Computerized Strategy) Method

Daniela Colombini, Enrico Occhipinti, Daniela Colombini, Enrico Occhipinti

• Publisher: CRC Press
• Year: 2018
• ISBN:
  9781351370196
• Edition: 1
• Topic: Business
• Subtopic: Service Industry
• Index: Business

This book covers how to analyze awkward working postures, particularly of the spine and lower limbs, in specific groups exposed. The methods covered suggests how to evaluate the postures correctly, taking account of the duration and sequence of the tasks involved, even in very complex scenarios where workers are involved with multiple tasks and work cycles varying from day to day. Excel spreadsheets located on the authors' website (www.epmresearch.org) have been developed to gather, condense, and automatically process the data. The tools serve to implement the strategy for calculating risk associated with exposure to awkward postures, i.e. the TACOS method. Included are 5 case studies which include physiotherapists, workers from construction, archaeological digs, vineyards, and kindergarten teachers.

Features

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• Provides a coherent definition of what the study of awkward postures is

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• Clarifies and explains which parameters need to be detected and analyzed for the study of the working postures

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• Defines the phases of a proper organizational study (e.g. tasks, postures, duration, and how often the postures will last) in the working cycle

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• Presents a new and original risk calculation model for awkward postures, with particular attention to the study of the spine and the lower limbs

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• Offers a free excel spreadsheet located on the authors' website which implements the strategy for calculating risk associated with exposure to awkward postures

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1 Introduction and Aim

Daniela Colombini and Enrico Occhipinti

Ergonomics of Posture and Movement International Ergonomics School (EPM-IES)

Contents

• 1.1 Meaning of “Postural Tolerability”
• 1.2 Remarks on Spinal Posture Studies Based on Biomechanical Methods
• 1.3 Analyzing the Tolerability of Working Postures for the Spine When Performing Manual Lifting Tasks, and for the Upper Limbs When Performing Repetitive Movements and/or Manual Lifting: Specific ISO Standards
• 1.4 Analyzing Spinal and Lower Limb Postures: The Aim of This Book

1.1 Meaning of “Postural Tolerability”

Whenever someone is faced with a risk factor of any kind, the first problem that arises is how to describe and assess it. This also applies to working postures.

Until the 1970s, there were no methods available for providing a standard description of working postures nor were there any criteria for assessing them, i.e., determining potential risks associated with different postures and forms of exposure.

However, this shortcoming began to be remediated around the time when standard methods were developed for describing and assessing working postures.

This section provides a brief overview of the various methods reported in the literature for describing and assessing postures, including the original method created by the authors (Chapter 4). The focus will be on the main aspects of postural analysis and on the possible criteria for conducting assessments, which nonetheless may still be “rule-of-thumb” and require further validation.

The earliest posture analysis methods were those of Priel (1974), Grieco et al. (1978), and Karhu et al. (1977), while more recent ones were published by Colombini et al. (1985) and Corlett et al. (1979), suggesting a more global approach towards analyzing working postures.

Most of the methods for working posture analysis do a satisfactory job of identifying and describing which postures to assess and how to work out the final scores, but we believe they do not provide enough practical examples, especially of complex multitask activities based on which reliable conclusions are drawn about their effectiveness.

None of the methods deliver a seamless transition from description to assessment. This is not because of a shortage of descriptive models, almost all of which are exhaustive; it is rather due to lack of models for evaluating working postures, especially ones where the spine and lower limbs are static. Consequently, the models do not depict their effects on the musculoskeletal system.

As stated by Corlett et al. (1979), it can be concluded that “our ability to measure is higher than our capacity for interpreting data.”

A meaningful contribution towards developing assessment methods will only be made when significant certainties are reported for the evaluation of postural tolerability.

What criteria underpin posture evaluation and tolerability analysis?

First, there needs to be a consensus that what is being assessed is not the posture per sè but how it is tolerated within a specific time, space, and operating environment. Hence, the question is: what postures can be defined as tolerable? The assumption put forward here is that, for postures to be tolerable, they must NOT

1. cause discomfort in the short term;
2. cause musculoskeletal disorders or diseases in the long term.

“Short-term discomfort” describes a feeling of fatigue and/or pain in a joint or ligament that develops within minutes, hours, or days. However, with regard to this first requirement, it should be stressed that preventing incapacitating injury is not sufficient: complete well-being and comfort must be ensured at all times.

There must be no doubt, theoretically or otherwise, regarding the second requirement either: postures must not generate specific diseases or disorders.

On the whole, while perhaps debatable and calling for more in-depth considerations, such an approach is still nonspecific. Nonetheless, it is obvious that, for any of the assessment methods to achieve predictive significance, rather than being an end in themselves, they must meet at least one, and preferably both, of the aforementioned requirements.

It is difficult to establish standard requirements, methods, and criteria for assessing posture due to the numerous factors that need to be taken into consideration, including:

1. a relatively large number of variables making up a posture;
2. the virtually infinite number of postural combinations;
3. the nonspecific nature of diseases and disorders related to awkward postures.

In the literature, the most common methods for evaluating awkward postures rely primarily on:

• electromyograms;
• direct and indirect intervertebral disc pressure measurements;
• the biomechanics of posture;
• posture acceptability from the psychophysical standpoint.

All these approaches can supply useful information regarding the extent to which muscles, discs, or joints, considered separately, can tolerate loads. However, postures cannot be deemed tolerable when only one structure is able to withstand a load: all of the body parts involved in adopting a specific posture must be safeguarded as a whole.

Last, psychophysical assessments—being largely subjective—are also touched on but can be affected by numerous detrimental factors. Motivation is one such factor, as is the physical fitness of the worker and the existence of conflicts at work.

The main purpose of this manual is not, however, to look meticulously into all the various posture analysis methods. Here, we will simply consider a handful of analytical approaches with reference to their ability to meet the two requirements that underlie posture tolerability testing.

Table 1.1 lists various tolerability measurement techniques and assessment methods, interpretation criteria, and whether or not they meet both requirements. The methods are often difficult to implement, having been largely developed and employed in research laboratories rather than in the field.

TABLE 1.1

Principal Methods for Assessing the Tolerability of Work-Related Awkward Postures

1.2 Remarks on Spinal Posture Studies Based on Biomechanical Methods

When looking at the postures adopted while lifting and carrying loads, it is common for the “compressive” forces between 200 and 600 or even 700 kg to compress the lumbar discs.

The question is where to set an acceptable limit for such forces, based on a combination of the size of the load and the postures adopted during lifting.

An answer might come from knowing that the part of the spine most sensitive to axial forces is the vertebral endplate cartilage, which has also been identified as an essential element in passive disc nutrition. Loads capable of causing microfractures of this structure have been examined on autopsy specimens and appear to be extremely variable and age dependent. The lower threshold for forces compressing the lumbar discs, especially in the 40-plus age groups, has been found to be around 250 kg.

Chaffin and Park (1973) studied 400 workers subjected to different types of lumbar axial forces over a period of 18 months and found that the incidence of low back pain (in the previous 12 months) was much higher in those subjected to axial forces between 250 and 600 kg and significantly higher when forces exceeded 650 kg, compared with workers normally subjected to lumbar axial forces below 250 kg.

Figure 1.1 shows some examples of lying, standing, sitting postures, with or without manual lifting of loads, accompanied by the estimation of the corresponding lumbar axial, analyzed with biomechanical methods.

Another problem is the posture adopted when axial forces on the lumbar spine are less than 250–350 kg. Which postures are acceptable and which are not?

FIGURE 1.1 Examples of postures: prone, standing, sitting, with or without manual lifting, indicating estimated lumbar spine loads, analyzed using biomechanical methods.

It is necessary to consider the theories developed by Kraemer (1985) on intervertebral disc nutrition mechanisms, bearing in mind that the structure is avascular. Kraemer proved the existence of a disc pressure threshold, below which nourishment can reach the disc but catabolites struggle to escape, and above which the reverse is true. This critical pressure threshold is approximately 80–100 kg for lumbar discs.

FIGURE 1.2 Results of biomechanical analyses in the study of lumbosacral loads in seated postures with the spine supported or unsupported, and with the upper limbs resting or not resting on the work surface. The average lumbar loads applied in the various positions are listed from the lowest to the highest. When the upper body is supported, the loads are statistically significantly lower than when there is no support, and all are lower than the critical load level of 80–100 kg (Colombini et al. 1985, 1986).

In this respect, the “best” postures are those that allow the disc to be nourished, with lumbar axial forces that alternate above and below the threshold. The “worst” postures are adopted when axial forces are constantly above the threshold. Even when axial forces are always below the threshold (as when sitting with the spine and upper limbs supported, as shown in Figure 1.2), the expulsion of catabolites from the disc may be hampered; if prolonged and fixed, the posture may still be somewhat awkward. However, such cases may be improved without undue effort, for example, by introducing frequent rotations with other tasks requiring a standing posture and/or with breaks and/or compensating exercises.

In conclusion, for postures that do not entail m...