The safety clothing, rubber safety boots, belt with lifting hooks and personal protectors can weight about 3 kg more than the normal work clothing including rubber boots. In order to evaluate the increase off the physical strain in logging work due to them, laboratory tests performed on tread mill were made. The physical strain increased 3–11% as estimated from heart rate and 4–8% as estimated from oxygen consumption measurements.
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The concepts central to ergonomic research connected with the amount of strain caused by work was studied. A model was made to describe the process of strain. The model includes the following concepts: load or stress, human input, worker, strain, renewal of human resources, output and their hierarchical units. Based on the quality of human input, the forest work was roughly divided into two categories: (1) work demanding primarily muscle activity and (2) neuro-sensory work. In the first group, especially in cutting work, the main part of the human input is intensive consumption of muscle energy. In addition, work load causes accidents, wear of skeletal and muscular systems and processes by noise, vibrations, and climate. Correspondingly, when operating forest machines, the human input is mainly neuro-sensory functions of the central nervous system. Work load causes directly the effects of low frequency vibration and of other work conditions. The model was tested on data from research of forest work.
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The physical strain put on forest workers and work time consumption during pulpwood cutting were compared when the bolts were stacked at the side of strip road, the strip road spacings being 15–25 m and 26–35 m, and when stacked at scattered points along the cutting strip.
When stacking at scattered points along cutting strip work time consumption was 17–21% and the heart rate 9–12% less than when stacking at the side of the strip road, strip road spacing being 15–25 m. When the strip road spacing was increased to 26–35 m, the time consumption increased by 18–30%, but the heart rate appeared unchanged. This result suggests that the forest worker compensates for increased physical strain caused by an increased stacking distance by changing his working technique and rate and by increasing the number of his breaks.
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