J. For. Res. 3:75-78 (1998) A Biomechanical Analysis of Industrial Forest Plantation Workers in East Kalimantan 1 Seca Gandaseca,* Tetsuhiko Yoshimura,*, 2 Toshiaki Yamamoto,** and Slamet Mulyono*** *Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan. **The University Forests, Faculty of Agriculture, Kyoto University, Kyoto 606-8502, Japan. ***Faculty of Forestry, Mulawarman University, Samarinda, Indonesia. The objectives of this study are to clarify physiological work loads and physical loads acting on the lumbar region of workers and to propose a safe work environment in tropical forestry operations. The research was conducted in the industrial forest plantations of East Kalimantan, Indonesia, in 1996. In this study, heart rates and the physical lumbar burden of industrial forest plantation work- ers were measured for three types of work, that is, weeding, planting and path clearing. In addition, the load moment at the Ls/St and the disc compression force were calculated using low-back biomechanical models. As a result, compression forces at the Ls/S i disc during weeding, planting and path clearing were estimated and found to be below the Action Limit (AL) by National Institute for Occupational Safety and Health (NIOSH). However, it was also found that some work posture types during path clearing by chain saw were sometimes above the AL. Key words: biomechanical model, compression force, forestry work, heart rates, load moment The industrial forest plantation in East Kalimantan was established in 1990 to compensate for the deforestation that was caused by overcutting and at the same time to move people from the overpopulated Jawa Island to the underpop- ulated Kalimantan Island. However, for many of these work- ers, East Kalimantan is far from their hometowns. In addition, it is located near the equator; therefore, these forestry workers are exposed to severe living and working conditions. A series of ergonomic studies (Seca et al., 1995a, b, 1997) and social and psychological studies (Slamet et al., 1995a, b, c) have been conducted in this area, to better understand and to improve such living and working conditions. Forestry workers often complain of physical disorders and most often experience stiffness or pain around their lumbar parts. Actually, low back pain is one of the more common and costly work-related musculoskeletal disorders. Control and prevention of job-related low back pain can be accomplished through the evaluation of job activities, identification of occu- pational risk factors and implementation of appropriate inter- ventions (Ness, 1996). Unnatural postures during work have the consequence of an increase in physical lumbar burden. Tatsukawa and Ohsato. (1988), Yamada et al. (1990) and Yamada et al. (1991) reported relationships between working stress and posture in Japanese forestry. The objectives of this study were to clarify physical loads acting on the lumbar region of workers and to propose a safe work environment for tropical forest operations. The research was conducted from August 11-13, 1996, in the industrial for- est plantations of E T. Inhutani in Long Nah, which is locat- ed in East Kalimantan (Fig. 1). This study especially focused on the load moment and the compression force at the L5/SI disc (lumbosacral disc), which were calculated using a static biomechanical model. The calculated load moments were I A part of this paper was orally presented at the 108th Annu- al Meeting of the Japanese Forestry Society (1997). 2 Corresponding author. compared to the recommendations of Tichauer (1978). The calculated compression forces were also compared to the Action Limit (AL) suggested by the National Institute for Occupational Safety and Health (NIOSH). At the same time, heart rates were recorded to study physiological work loads on industrial forest plantations. Methods 1 Measurements Subjects were six industrial forest plantation workers engaged in three types of work, that is, weeding, planting and path clearing. Personal data and types of work are shown in Table 1. Weeding involved the cutting of undergrowth using a hatchet which was 1 kg in weight. Planting consisted of car- rying a hoe and seedlings, digging a hole and planting the seedlings. The planted tree species was Shorea leprosula. The weight of a hoe and a seedling was 1 kg and 0.1 kg, respec- tively. One worker carried one hoe and 20 seedlings, which were planted one after another. In the calculation, the work- er was supposed to carry 10 seedlings while walking, since we considered 10 to be the average. For path clearing, trees, including tall weeds, were cut using a chain saw which was 17 kg in weight. The path clearing is often done for the prepa- ration of enrichment planting, in which natural forests are cut in line and useful species are planted there while the existing trees are expected to protect seedlings (Asakawa, 1994). The forestry workers were equipped with heart rate mem- ory devices, and their heart rates were measured every 10 sec- onds automatically. In advance, each worker underwent a step test. We estimated their work loads based on collected data, using the method described by Seca et al. (1997). At the same time, we recorded their work postures using video cameras. Work postures were classified according to seven typical postures (Fig. 2). Table 2 and Fig. 3 show body segment angles of the seven postures shown in Fig. 2. We measured frequency of each type of posture at one sec