RECOMMENDED MAXIMUM HOLDING TIMES FOR PREVENTION OF DISCOMFORT OF STATIC STANDING POSTURES

The aim of the present study was threefold; (1) to analyze the influen ce of posture on the maximum holding time (MHT), (2) to study the poss ibility of classifying postures on the basis of MHT, and (3) to develo p ergonomic recommendations for the MHT of categories of postures. For these purposes data concerning the MHT of 19 symmetric standing postu res from 7 experimental studies from the literature were analyzed. All postures were defined by the position of the hands with respect to th e feet. For each posture the mean MHT over all available data was calc ulated. The results show that for the 19 postures this mean MHT ranges from 2 to 35 minutes. For a given posture the variation in MHT betwee n different studies is large. It seems that in particular the type of task (boring versus interesting) performed while maintaining the postu re has a great influence on the MHT. On the basis of the mean MHT post ures were classified into three classes. Comfortable postures are defi ned as postures that have a MHT of more than 10 minutes and are recomm ended not to be maintained more than 2 minutes. Moderate postures have a MHT of 5-10 minutes and are recommended to be maintained for less t han 1 minute. Uncomfortable postures, having a MHT up to 5 minutes, ar e not acceptable. It is estimated that with theses recommendations a d iscomfort of more than 2 (weak discomfort) on the Borg 10-point rating scale (up to maximum discomfort) is prevented for at least 50% of the population, and a discomfort of more than 5 (strong discomfort) is pr evented for at least 95% of the population. The recommended holding ti me valid for each class corresponds with the lowest recommended holdin g time of that class. Therefore the recommendations are safe for all p ostures. Our classification of postures corresponds well with classifi cations based on biomechanical and anthropometric data and is more str ict than the OWAS-classification. Relevance to industry Many work situ ations in industry require static standing postures. Maintaining a pos ture for a longer period of time may lead to feelings of discomfort. T his study presents recommendations for maximum holding time based on e xperimental data.