Journal of Electromyography and Kinesiology 24 (2014) 404–411
Contents lists available at ScienceDirect
Journal of Electromyography and Kinesiology journal homepage: www.elsevier.com/locate/jelekin
Upper extremity kinematic and kinetic adaptations during a fatiguing repetitive task Jin Qin a,b,⇑, Jia-Hua Lin b, Gert S. Faber c, Bryan Buchholz a, Xu Xu b a
Department of Work Environment, University of Massachusetts, Lowell, MA 01854, USA Liberty Mutual Research Institute for Safety, Hopkinton, MA 01748, USA c Faculty of Human Movement Sciences, VU University Amsterdam, The Netherlands b
a r t i c l e
i n f o
Article history: Received 28 August 2013 Received in revised form 8 January 2014 Accepted 2 February 2014
Keywords: Repetitive work Kinematic variability Age Upper extremity
a b s t r a c t Repetitive low-force contractions are common in the workplace and yet can lead to muscle fatigue and work-related musculoskeletal disorders. The current study aimed to investigate potential motion adaptations during a simulated repetitive light assembly work task designed to fatigue the shoulder region, focusing on changes over time and age-related group differences. Ten younger and ten older participants performed four 20-min task sessions separated by short breaks. Mean and variability of joint angles and scapular elevation, joint net moments for the shoulder, elbow, and wrist were calculated from upper extremity kinematics recorded by a motion tracking system. Results showed that joint angle and joint torque decreased across sessions and across multiple joints and segments. Increased kinematic variability over time was observed in the shoulder joint; however, decreased kinematic variability over time was seen in the more distal part of the upper limb. The changes of motion adaptations were sensitive to the task-break schedule. The results suggested that kinematic and kinetic adaptations occurred to reduce the biomechanical loading on the fatigued shoulder region. In addition, the kinematic and kinetic responses at the elbow and wrist joints also changed, possibly to compensate for the increased variability caused by the shoulder joint while still maintaining task requirements. These motion strategies in responses to muscle fatigue were similar between two age groups although the older group showed more effort in adaptation than the younger in terms of magnitude and affected body parts. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction Work-related musculoskeletal disorders (WMSDs) associated with repetitive work has been identified as a significant occupational health problem (National Research Council, 2001; Bernard, 1997). Recent trends in global working life suggest that the number of occupations characterized by long-lasting low-level loads, and/or performing repetitive operations (e.g. short-cycle assembly work, office work) is increasing (Mathiassen, 2006). Repetitive movements during prolonged work, even though ‘‘light’’ in terms of external load involved, could lead to cumulative biomechanical loading, i.e. muscle fatigue, defined as a decrease in functional capacity to perform physical actions and/or to maintain required force production (Jensen et al., 2000). Muscle fatigue may play an important initiating role in musculoskeletal disorders, particularly ⇑ Corresponding author. Address: Department of Work Environment, University of Massachusetts, One University Avenue, Lowell, MA 01854, USA. Tel.: +1 978 934 3250x3915; fax: +1 978 452 5711. E-mail address: [email protected] (J. Qin). http://dx.doi.org/10.1016/j.jelekin.2014.02.001 1050-6411/Ó 2014 Elsevier Ltd. All rights reserved.
in the neck-shoulder region (Hermans and Spaepen, 1997; Rempel et al., 1992; Takala, 2002). The upper limb, particularly the shoulder region, is especially susceptible to the occurrence of musculoskeletal disorders caused by repetitive work (Larsson et al., 2007; National Research Council, 2001; van Rijn et al., 2010). Loading on the shoulder joint has been studied while performing isometric contractions (Antony and Keir, 2010), overhead activities (Ebaugh et al., 2006; Sood et al., 2007), assembly tasks (Bosch et al., 2009, 2007), and computer work (Kimura et al., 2007). Most of these studies used electromyography of the shoulder muscles as the outcome measure and did not report kinematics of the arm. Kinematics and kinetics affect muscle loading and, therefore, are important factors for understanding the injury mechanism of WMSDs and providing a scientific base for workplace interventions. Studies have shown altered kinematic patterns in response to muscle fatigue for the upper extremity. For example, altered scapulothoracic motion and humeral head migration were observed following shoulder muscle fatigue (Chopp et al., 2010; Ebaugh et al., 2006). In a repetitive sawing task with elbow extensor fatigue development (Cote et al., 2002),
J. Qin et al. / Journal of Electromyography and Kinesiology 24 (2014) 404–411
motion amplitudes decreased at the elbow and increased at all other joints (wrist, shoulder and trunk). However, most studies only reported kinematics or kinetics before and after muscle fatigue protocol, and little is known about the patterns of changes of these variables during muscle fatigue development. Motor variability, a cycle-to-cycle variability in kinematics and/ or muscle activation (Srinivasan and Mathiassen, 2012), has received increasing interest regarding its potential effect on health in working life. Emerging evidence has shown that motor variability is associated with muscle fatigue, pain, external working conditions, individual traits, and performance (Srinivasan and Mathiassen, 2012). The biomechanical redundancy of the upper limb multi-joint kinematic system allows variability in movements and makes it possible to alter motor strategies of movement organization in response to muscle fatigue (Madeleine, 2010). Variation of physical load has been considered to be beneficial in reducing risks of musculoskeletal disorders (Mathiassen, 2006). Increased upper extremity kinematic variability and altered motor coordination associated with muscle fatigue without affecting task performance has been reported (Fuller et al., 2011, 2009; Gates and Dingwell, 2008, 2011). In those previous studies, the task protocol involved either repetitive touching between two targets at shoulder height in front of the subject’s midline while maintaining the whole arm motion in the horizontal plane, or repetitive anterior– posterior directional movements against resistance until voluntary exhaustion. Such tasks were relatively high in intensity therefore participants were only able to maintain the task requirements for a short time (
Contents lists available at ScienceDirect
Journal of Electromyography and Kinesiology journal homepage: www.elsevier.com/locate/jelekin
Upper extremity kinematic and kinetic adaptations during a fatiguing repetitive task Jin Qin a,b,⇑, Jia-Hua Lin b, Gert S. Faber c, Bryan Buchholz a, Xu Xu b a
Department of Work Environment, University of Massachusetts, Lowell, MA 01854, USA Liberty Mutual Research Institute for Safety, Hopkinton, MA 01748, USA c Faculty of Human Movement Sciences, VU University Amsterdam, The Netherlands b
a r t i c l e
i n f o
Article history: Received 28 August 2013 Received in revised form 8 January 2014 Accepted 2 February 2014
Keywords: Repetitive work Kinematic variability Age Upper extremity
a b s t r a c t Repetitive low-force contractions are common in the workplace and yet can lead to muscle fatigue and work-related musculoskeletal disorders. The current study aimed to investigate potential motion adaptations during a simulated repetitive light assembly work task designed to fatigue the shoulder region, focusing on changes over time and age-related group differences. Ten younger and ten older participants performed four 20-min task sessions separated by short breaks. Mean and variability of joint angles and scapular elevation, joint net moments for the shoulder, elbow, and wrist were calculated from upper extremity kinematics recorded by a motion tracking system. Results showed that joint angle and joint torque decreased across sessions and across multiple joints and segments. Increased kinematic variability over time was observed in the shoulder joint; however, decreased kinematic variability over time was seen in the more distal part of the upper limb. The changes of motion adaptations were sensitive to the task-break schedule. The results suggested that kinematic and kinetic adaptations occurred to reduce the biomechanical loading on the fatigued shoulder region. In addition, the kinematic and kinetic responses at the elbow and wrist joints also changed, possibly to compensate for the increased variability caused by the shoulder joint while still maintaining task requirements. These motion strategies in responses to muscle fatigue were similar between two age groups although the older group showed more effort in adaptation than the younger in terms of magnitude and affected body parts. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction Work-related musculoskeletal disorders (WMSDs) associated with repetitive work has been identified as a significant occupational health problem (National Research Council, 2001; Bernard, 1997). Recent trends in global working life suggest that the number of occupations characterized by long-lasting low-level loads, and/or performing repetitive operations (e.g. short-cycle assembly work, office work) is increasing (Mathiassen, 2006). Repetitive movements during prolonged work, even though ‘‘light’’ in terms of external load involved, could lead to cumulative biomechanical loading, i.e. muscle fatigue, defined as a decrease in functional capacity to perform physical actions and/or to maintain required force production (Jensen et al., 2000). Muscle fatigue may play an important initiating role in musculoskeletal disorders, particularly ⇑ Corresponding author. Address: Department of Work Environment, University of Massachusetts, One University Avenue, Lowell, MA 01854, USA. Tel.: +1 978 934 3250x3915; fax: +1 978 452 5711. E-mail address: [email protected] (J. Qin). http://dx.doi.org/10.1016/j.jelekin.2014.02.001 1050-6411/Ó 2014 Elsevier Ltd. All rights reserved.
in the neck-shoulder region (Hermans and Spaepen, 1997; Rempel et al., 1992; Takala, 2002). The upper limb, particularly the shoulder region, is especially susceptible to the occurrence of musculoskeletal disorders caused by repetitive work (Larsson et al., 2007; National Research Council, 2001; van Rijn et al., 2010). Loading on the shoulder joint has been studied while performing isometric contractions (Antony and Keir, 2010), overhead activities (Ebaugh et al., 2006; Sood et al., 2007), assembly tasks (Bosch et al., 2009, 2007), and computer work (Kimura et al., 2007). Most of these studies used electromyography of the shoulder muscles as the outcome measure and did not report kinematics of the arm. Kinematics and kinetics affect muscle loading and, therefore, are important factors for understanding the injury mechanism of WMSDs and providing a scientific base for workplace interventions. Studies have shown altered kinematic patterns in response to muscle fatigue for the upper extremity. For example, altered scapulothoracic motion and humeral head migration were observed following shoulder muscle fatigue (Chopp et al., 2010; Ebaugh et al., 2006). In a repetitive sawing task with elbow extensor fatigue development (Cote et al., 2002),
J. Qin et al. / Journal of Electromyography and Kinesiology 24 (2014) 404–411
motion amplitudes decreased at the elbow and increased at all other joints (wrist, shoulder and trunk). However, most studies only reported kinematics or kinetics before and after muscle fatigue protocol, and little is known about the patterns of changes of these variables during muscle fatigue development. Motor variability, a cycle-to-cycle variability in kinematics and/ or muscle activation (Srinivasan and Mathiassen, 2012), has received increasing interest regarding its potential effect on health in working life. Emerging evidence has shown that motor variability is associated with muscle fatigue, pain, external working conditions, individual traits, and performance (Srinivasan and Mathiassen, 2012). The biomechanical redundancy of the upper limb multi-joint kinematic system allows variability in movements and makes it possible to alter motor strategies of movement organization in response to muscle fatigue (Madeleine, 2010). Variation of physical load has been considered to be beneficial in reducing risks of musculoskeletal disorders (Mathiassen, 2006). Increased upper extremity kinematic variability and altered motor coordination associated with muscle fatigue without affecting task performance has been reported (Fuller et al., 2011, 2009; Gates and Dingwell, 2008, 2011). In those previous studies, the task protocol involved either repetitive touching between two targets at shoulder height in front of the subject’s midline while maintaining the whole arm motion in the horizontal plane, or repetitive anterior– posterior directional movements against resistance until voluntary exhaustion. Such tasks were relatively high in intensity therefore participants were only able to maintain the task requirements for a short time (
