Laboratory work with automatic pipettes: a study on how pipetting affects the thumb.

The aim of this study was to assess the strain that is exerted on the thumb when working with automatic pipettes. The study consisted of three parts: a survey concerning stress-related symptoms in general and in the thumb in particular, a study of the working conditions in the laboratory with the help of a video-film, and a power test. In the survey the Nordic Council of Ministers' questionnaire and a newly developed questionnaire about the thumb were used. A usual and frequently carried out analysis that included several different methods of pipetting was filmed on video. The power test measured two things, the power that is necessary to press down the button of the pipette into different positions and the maximal strength when performing a movement in the same direction. It was shown that the strain on the thumb for a woman with weak muscular structures is unacceptably high. The symptoms increase with the amount of time spent with pipetting and with age. In addition, pipetting is done in a position where the thumb is not stable but nevertheless has to work to stabilize the grip around the pipette and to press down the button of the pipette. Therefore the muscles have to work both as mobilizing and stabilizing structures. It is concluded, therefore, that some form of automation ought to be taken into consideration if the amount of pipetting work tends to increase. The pipettes should be constructed with as little button resistance as possible and the handle should be designed to fit different hand sizes.