"EFEITO DA POSTURA CORPORAL E MOVIMENTOS REPETITIVOS NA CARGA MUSCULAR DE OPERADORES DE HARVESTER E FORWARDER"

Abstract

The advance of mechanization in timber harvesting operations has brought improvements in the productive capacity of machines and workstations with air-conditioned cabins, providing greater comfort and safety for operators. Despite this, there are some ergonomic risks in forestry machine operations in relation to inadequate body postures and repetition of movements, exposing operators to high muscle loads and risks of Repetitive Strain Injury and Work-Related Musculoskeletal Disorders. In view of the above, this research aimed to evaluate the effect of body posture and repetitive movements on the muscle load of harvester and forwarder operators, with a view to identifying the potential impacts on health and proposing improvements in working conditions. The study was carried out in a forestry company located in the Midwest region of Brazil, in seven-year-old Eucalyptus grandis x Eucalyptus urophylla hybrid stands, during harvesting and logging operations carried out by harvester and forwarder, respectively. Seven harvester and four forwarder operators were evaluated on a daily basis as they carried out the operations over a six-day work schedule. A time study was carried out to determine working times and obtain the productivity of the operations. The operators were filmed at their workstations using cameras installed in the machine cabins, in order to assess the operators' body postures using joint angles, using the RULA methodology and the computer tool Kinebot®. The operators' repetitive movements were assessed using the OCRA methodology, as set out in ISO 11228-3:2014, with the movements (technical actions) being characterized and counted based on daily 12-minute filming. The muscle load on different parts of the operators' bodies was assessed using the infrared thermography technique, which captures heat in the form of infrared radiation emitted by the body. The images were recorded before and after the working day throughout the working day. The results indicated that the operators, on average, spent 75% of their working day operating both machines, giving an average productivity of 92 trees/PMH-1 and 4.5 buckets/PMH-1 in felling and extraction, respectively. The postural analysis showed a greater risk of injury in the neck and trunk regions, although attention should be paid to the shoulder regions on both machines. An average of 46,116 hand movements were recorded for harvester operators and 43,160 for forwarder operators, resulting in OCRA exposure indices of 14.0 and 15.9 for harvesters and forwarders, respectively, and therefore a high level of risk to operators' health. The muscle load assessment indicated significant temperature variations between the periods before and after the working day for the operators' face, orbital and hand regions. The lumbar region did not show any significant temperature variation, but there was a 1.1ºC increase in temperature by the fourth day, indicating that there was a peak in temperature and a greater risk of injury in the middle of the working day. It was possible to conclude that the operators of the forestry machines studied are subject to ergonomic risks due to inadequate body postures in some stages of the work and high repetitive movements, impacting on the muscular load of parts of the body as evidenced by the functional diagnosis using infrared thermography.