work joules indicate the level of bodily stress and, especially in heavy work, they can be used to assess the level of effort, to determine necessary rest periods and to compare the energetic efficiency of different tools and different ways of arranging the work. In this context it should be clearly understood that energy consumption measures only the level of physical effort, it tells us nothing about mental stress, the demands the work may make in alertness, concentration or skill, nor about any special physical problems such as excessive heat or static loads from awkward postures.