Academic journal article Central European Journal of Public Health

A New Approach to the Evaluation of Local Muscular Load While Typing on a Keyboard

Academic journal article Central European Journal of Public Health

A New Approach to the Evaluation of Local Muscular Load While Typing on a Keyboard

Article excerpt


In the Czech Republic, the incidence of occupational diseases due to the long-term excessive unilateral load of the upper extremities is increasing during recent years. The frequent cause is the prolonged excessive burden on small muscle groups of the forearm and hand, so-called local muscular load. This burden is evaluated primarily using integrated electromyography (iEMG). Objectification of local muscular load is performed mainly for work associated with high numbers of repeated unilateral movements (in forced pace of work, assembly work, minor installation work demanding on precision, typing, etc.). Optionally, it is at work, in which large muscular forces are expended (handling heavy loads, applying high finger forces in assembly tasks, work associated with unfavourable working postures of the upper limbs, etc.).

The evaluation of load with this method is based on the limits set by Government Decree no. 361/2007 Coll., as amended, establishing conditions of health protection at work. We evaluate the average time-weighted value of the percent maximum voluntary contraction (%MVC), the number of expended large muscle forces in the range of 55-70% MVC, incidence of the over-limit muscle forces above 70% MVC, and the whole shiftnumber of unilateral repetitive movements of hands and forearms with regard to expended forces. In terms of working with a computer, it is the excessive number of repeated unilateral movements with regard to expended muscle strength during typing and using a mouse, which represents one of the potential risk factors for an occupational/work related disease due to overload.

The evaluation of movements during the typing is currently performed in three ways: the method of in-situ observation takes place several times over a limited period of time in order to determine the movements per minute of the hands and forearms. The worker is under the direct supervision of the evaluating person. It can stress him/her, he or she can work at a different speed than usual, and may make more mistakes.

Analysis of the occupational activities from video recordings is carried out in a similar way as the method of in-situ observation, i.e. few times over a limited period of time to determine the number of movements per minute of the hands and forearms. During video recording, the evaluated worker can be exposed to the same level of stress as in the first method.

Evaluation of the amount of written text has the disadvantage that the final text does not include complete information concerning the total amount of work done on the computer keyboard. Relevant examples are typing errors, i.e. characters (whole words, sentences or paragraphs) that were written during the work and subsequently deleted. Furthermore, this includes the "in the text invisible" keystrokes such as "Shift" or "Caps Lock" when writing capital letters, pressing "Delete" or "BackSpace" when correcting typos, pressing "Tab" or "Enter" when going through web forms, etc. Additionally, it is a combination of keystrokes, such as "Ctrl + A" to select text, "Ctrl + C" to copy or "Ctrl + X" to cut the text and then "Ctrl + V" to paste it. These keystrokes are not seen in the final text, and quite often, they are a very abundant component when creating different types of documents.

For the above-mentioned reasons, none of those standard methods can objectively determine the actual number of movements during typing or using a mouse. Therefore, improvement of the existing methodology for measuring and evaluating local muscular load while working on a computer is needed, especially for the work which is characterised by a high frequency of entering data into the computer via keyboard (e.g. accountant, clerk, secretary, etc.). In an effort to improve objectivity and accuracy of determination of the number of movements while working on the computer and of the evaluation of the local muscular load, we decided to combine iEMG with keystroke dynamics (KD) method. …

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