Use of physiological criteria for improving physical work conditions

Physical work is still present in many countries, specially in developing ones. The physiological analysis of the work load could be conducted through two different ways, referring to his energetic cost and/or to the mechanical power of the human motor. The purpose of ergonomics is to organize any physical professional task in order to maintain the workers as much as possible inside the limits of a fatiguing activity. The process of fatigue affects differently a "general activity" and a "local work." If a worker is engaged in a general hard activity, like carrying a load or pushing a trolley, an increase of oxygen consumption or/and an acceleration of the heart rate could be observed. This latter, allowing to estimate the oxygen cost of the work, is more affected if the work is performed in a hot environment. In order to establish the ratio between the data observed at the work place and the maximal working capacity of the organism, it is possible to experiment with the physiological effects of transitory increases of the work stress, by increasing the load or/and the frequency of the repetition of the "unit" of work done. When the task could be described in terms of local work, the correct methodology is based upon the general rules established respectively for the static and the dynamic work. In both the cases, it is possible to determine the critical rate of the muscular activity, the part of the muscular capacity engaged at the work place and the probable time for local exhaustion, in order to limit the duration of each period of work. It should be remembered that 50 years ago, Lucien Brouha proposed that heart rate determinations at work be used as a criteria for a better organization of human work by a non-sophisticated method.