Task-specific postures in low-seam underground coal mining Susan M. Moore * , Jonisha P. Pollard, Mary Ellen Nelson Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, Office of Mine Safety and Health Research, Human Factors Branch, United States article info Article history: Received 17 March 2011 Received in revised form 21 October 2011 Accepted 20 January 2012 Available online 28 February 2012 Keywords: Knee Kneeling Crawling Posture Mining Coal abstract The objective of this study was to determine low-seam mine worker exposure to various postures as they pertain to job classifications and job tasks. Sixty-four mine workers from four low-seam coal mines participated. The mine workers reported the tasks they were required to complete and the two postures they used most frequently to perform them. They were provided with a schematic of postures from which to select. The two postures reported most frequently were identified for each task along with the job classification of the workers performing the tasks. Of the 18 tasks reported, over two thirds were performed by at least two different job classifications and over one third were performed by four or more job classifications. Across tasks, the postures used appeared to vary greatly. However, when grouped by job classification, the most frequently reported posture across all job classifications was kneeling near full flexion. Operating the continuous miner was associated with frequent squatting and was likely used because it affords great mobility, allowing operators to move quickly to avoid hazards. However, for environments with a restricted vertical height such as low-seam mining, the authors recommend squatting be avoided as data demonstrates that large amounts of femoral rollback and high muscle activity for the extensors when performing lateral lifts in this posture. Kneeling near full flexion was reported as the most frequently used posture by all job classifications and was likely due to the fact that it requires the least amount of muscle activity to maintain and has reduced pressures at the knee. However, the authors recommend this posture be avoided when performing lateral lifting tasks. Like squatting, kneeling near full flexion results in increased femoral rollback and may increase the stresses applied to the meniscus. Unlike lateral lifting, maintaining a static posture results in knee loading and muscle activity such that the mine worker should consider kneeling near full flexion and sitting on their heels. Although kneeling near full flexion is associated with injuries, there are benefits to this posture that are realized when statically kneeling (minimal muscle activity, allows worker to maintain an upright torso in low heights, and decreased loading at the knee). However, cartilage is avascular and nourished by synovial fluid. Therefore, one should frequently rotate between postures, assuming a more upright kneeling posture when possible and frequently fully flexing and extending the knee allowing nutrients to the cartilage. Relevance to industry: In 2009, over one fourth of underground coal mines that produced coal in the United States were considered low seam with an average working height of <109.2 cm (MSHA, 2009) restricting workers to their knees. Data exists regarding the biomechanical implications of kneeling postures and demonstrates the possibility of detrimental consequences to varying degrees for each posture. With each posture posing a different level of exposure to musculoskeletal disorder risk factors, it is essential to determine the postures mine workers use to perform their job tasks and how their postural options are restricted by the low-seam underground mining environment. Published by Elsevier B.V. 1. Introduction In 2009, 532 underground coal mines produced a total of 330.8 million tons of coal (MSHA, 2009). Of these mines, 148 (28%) were considered low seam with a seam height of less than 109.2 cm and produced 19.1 million tons of coal. For economic reasons, the seam height of the coal corresponds with the working height (from mine floor to mine roof) of the mine. Thus, at least 6% of underground coal produced in the United States in 2009 came from a mine where workers were restricted. Individuals who work in underground coal mines face a variety of challenges. Many studies have demonstrated that low-seam * Corresponding author. 626 Cochrans Mill Road, PO Box 18070, Pittsburgh, PA 15236, United States. Tel.: þ1 412 386 6613. E-mail address: SMMoore@cdc.gov (S.M. Moore). Contents lists available at SciVerse ScienceDirect International Journal of Industrial Ergonomics journal homepage: www.elsevier.com/locate/ergon 0169-8141/$ e see front matter Published by Elsevier B.V. doi:10.1016/j.ergon.2012.01.002 International Journal of Industrial Ergonomics 42 (2012) 241e248