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Holding determined body postures during work is connected with energy expenditure. The more forced the posture is, the more muscles take active part in holding and stabilizing the working posture. In forest operations the most share of awkward (forced) working postures occur during the tree felling with a chainsaw. It is also one of the hardest activities in motor−manual timber harvesting process. The group of 10 experienced fellers in the age of 47.5±7.3 years was studied. The research was carried out on four Scots pine clear−cuts in western Poland, in spring and autumn without snow cover. The average air temperature was 7.1±4.8°C, and humidity amounted to 72±6.7%. In the simulation study the fellers cut thin wood slices from 30 cm stumps. The stumps were located close to each other in order to minimize the influence of passes from one to another. The diameter of stumps was selected so that it wouldn't exceed the effective length of the chainsaw bar. The felling was carried out with the chainsaw Stihl MS 361 with the power of 3.4 kW and weight of 7.5 kg. Net energy expenditure (NEE) was determined using the pulmonary ventilation measurement (MWE−1 meter) during simulation of felling in 4 working postures (fig.). The lowest energy expenditure was observed for kneeling down on one knee and squatting: 16.4 and 16.9 kJ/min, respectively. Standing bent forward working postures feature statistically higher energy expenditure, reaching 19.9 kJ/min with straight legs and 22.1 kJ/min with bent legs (p<0.05). The realized research confirmed that body posture during felling with a chainsaw influences the level of the feller's physical workload. Standing bent postures cause energy consumption which is higher than during squatting and kneeling on one knee. The most preferred working posture, from the point of view of energy expenditure and biomechanical workload during felling, is standing bent posture with straight legs. The other postures, especially squatting, can be used regularly for a short time in order to unburden a lumbar part of spine. Applying working postures that require less energy during felling with the chainsaw may contribute to reducing the work heaviness on the feller's workstation.
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