The Foot 46 (2021) 101771 Available online 25 December 2020 0958-2592/© 2020 Elsevier Ltd. All rights reserved. Effects of corrective insole on leg muscle activation and lower extremity alignment in rice farmers with pronated foot: a preliminary report Agung Kristanto a, c , Manida S. Neubert b, c, *, Michael T. Gross d , Rungthip Puntumetakul c, e , David B. Kaber f , Weerapat Sessomboon a a Department of Industrial Engineering, Faculty of Engineering, Khon Kaen University, Khon Kaen, Thailand b Program of Production Technology, Faculty of Technology, Khon Kaen University, Khon Kaen, Thailand c Research Center in Back, Neck, Other Joint Pain and Human Performance (BNOJPH), Khon Kaen, Thailand d Division of Physical Therapy, Department of Allied Health Sciences, University of North Carolina at Chapel Hill, NC, USA e School of Physical Therapy, Faculty of Associated Medical Sciences, Khon Kaen University, Khon Kaen, Thailand f Department of Industrial and Systems Engineering, University of Florida, Gainesville, FL, USA A R T I C L E INFO Keywords: Medial wedge insole Muscle activity Foot pronation Lower extremity alignment Working surface condition ABSTRACT Background: Execution of strenuous activities in conjunction with slippery and viscous muddy working terrain in rice cultivation leads to a high prevalence of farmer musculoskeletal disorders and malalignments. Recom- mended intervention strategies originally designed for congenitally disabled individuals may also be applicable to farmers, including simple corrective wedges to reduce foot eversion. The objective of the present study was to conduct a preliminary investigation of the effects of corrective wedges on lower extremity muscle activity and alignment when subjects stood on fat rigid ground or muddy terrain, simulating typical work conditions encountered by the unique but populous Thai rice farming workforce. Methods: Nine healthy farmers with pronated feet were recruited to participate and wedges were custom fabricated for each farmer based on physical therapy assessment and use of rapid prototyping techniques. Par- ticipants were asked to stand barefoot or with wedges on the two surface types. Results: Results revealed foot pronation and knee valgus to improve (ranging, on average between 5.5 and 16.1 degrees) when participants were equipped with corrective wedges. The muscle activity of the peroneus longus and the tibialis anterior increased for muddy terrain, as compared with the rigid surface. In general, the wedges induced less tibialis anterior activity and greater peroneus longus activity, compared to when participants were standing barefoot. An elevation in evertor muscle activity may refect stretching of the shortened muscle as a result of the reduced degree of foot pronation. Conclusions: Findings demonstrate potential benefts of corrective insole usage for farmers with pronated feet, including improved lower extremity alignment and invertor muscle activity reduction for both rigid and muddy terrains. 1. Introduction The extreme environment and strenuous work requirements of certain rice cultivation processes causes farmers to develop a high prevalence of musculoskeletal disorders (MSDs) and malalignments in various body parts [1,2]. In a recent study [3], foot pronation, which is defned by Horwood and Chockalingam [4] as a range of motion within the foot that makes the foot more prone to the support surface, was identifed as the predominant disorder among rice farmers in Khon Kaen, Thailand, with a prevalence of 36.1%. Excessive foot pronation may be greater than that required by the individual to adjust to morphology or forces imposed on the musculoskeletal system by gait or another action. Such abnormal body alignments may occur in rice farmers due to working conditions in rice paddy felds. A previous investigation of risk factors showed that years of farming experience strongly correlated with the specifc type of foot malalignment [3]. Rice farming in Thailand is primarily comprised of manual labor (National Statistical Offce), including frequent lifting of heavy loads with awkward postures and prolonged standing on both muddy and fat rigid terrain [5]. Progressive structural deformity of weight-bearing foot * Corresponding author at: Program of Production Technology, Faculty of Technology, Khon Kaen University, Khon Kaen 40002, Thailand. E-mail address: manida@kku.ac.th (M.S. Neubert). Contents lists available at ScienceDirect The Foot journal homepage: www.elsevier.com/locate/foot https://doi.org/10.1016/j.foot.2020.101771 Received 11 March 2020; Received in revised form 9 December 2020; Accepted 9 December 2020