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Robust estimation of lumbar joint forces in symmetric and asymmetric lifting tasks via large-scale electromyography-driven musculoskeletal models. J Biomech 2022; 144:111307. [DOI: 10.1016/j.jbiomech.2022.111307] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2022] [Revised: 08/25/2022] [Accepted: 09/13/2022] [Indexed: 11/18/2022]
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Banks JJ, Umberger BR, Caldwell GE. EMG optimization in OpenSim: A model for estimating lower back kinetics in gait. Med Eng Phys 2022; 103:103790. [PMID: 35500997 DOI: 10.1016/j.medengphy.2022.103790] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2021] [Revised: 10/22/2021] [Accepted: 03/14/2022] [Indexed: 12/13/2022]
Abstract
Participant-specific musculoskeletal models are needed to accurately estimate lower back internal kinetic demands and injury risk. In this study we developed the framework for incorporating an electromyography optimization (EMGopt) approach within OpenSim (https://simtk.org/projects/emg_opt_tool) and evaluated lower back demands estimated from the model during gait. Kinematic, external kinetic, and EMG data were recorded from six participants as they performed walking and carrying tasks on a treadmill. For evaluation, predicted lumbar vertebral joint forces were compared to those from a generic static optimization approach (SOpt) and to previous studies. Further, model-estimated muscle activations were compared to recorded EMG, and model sensitivity to day-to-day EMG variability was evaluated. Results showed the vertebral joint forces from the model were qualitatively similar in pattern and magnitude to literature reports. Compared to SOpt, the EMGopt approach predicted larger joint loads (p<.01) with muscle activations better matching individual participant EMG patterns. L5/S1 vertebral joint forces from EMGopt were sensitive to the expected variability of recorded EMG, but the magnitude of these differences (±4%) did not impact between-task comparisons. Despite limitations inherent to such models, the proposed musculoskeletal model and EMGopt approach appears well-suited for evaluating internal lower back demands during gait tasks.
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Affiliation(s)
- Jacob J Banks
- University of Massachusetts Amherst, Department of Kinesiology, 110 Totman Building, 30 Eastman Lane, Amherst, MA 01003, United States; Beth Israel Deaconess Medical Center, Center for Advanced Orthopaedic Studies, 330 Brookline Avenue, RN 115, Boston, MA 02215, United States; Harvard Medical School, Department of Orthopaedic Surgery, Boston, MA 02115, United States.
| | - Brian R Umberger
- University of Michigan, School of Kinesiology, 830 North University Avenue, Ann Arbor, MI 48109, United States.
| | - Graham E Caldwell
- University of Massachusetts Amherst, Department of Kinesiology, 110 Totman Building, 30 Eastman Lane, Amherst, MA 01003, United States.
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Botter A, Marateb HR, Afsharipour B, Merletti R. Solving EMG-force relationship using Particle Swarm Optimization. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2012; 2011:3861-4. [PMID: 22255182 DOI: 10.1109/iembs.2011.6090959] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
The Particle Swarm Optimization (PSO) algorithm is applied to the problem of "load sharing" among muscles acting on the same joint for the purpose of estimating their individual mechanical contribution based on their EMG and on the total torque. Compared to the previously tested Interior-Reflective Newton Algorithm (IRNA), PSO is more computationally demanding. The mean square error between the experimental and reconstructed torque is similar for the two algorithms. However, IRNA requires multiple initializations and tighter constraints found by trial-and-errors for the input variables to find a suitable optimum which is not the case for PSO whose initialization is random.
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Affiliation(s)
- Alberto Botter
- Laboratory for Engineering of the Neuromuscular System, LISiN,Department of Electronics, Politecnico di Torino, Torino, Italy.
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Brown SHM, Gerling ME. Importance of sarcomere length when determining muscle physiological cross-sectional area: A spine example. Proc Inst Mech Eng H 2012; 226:384-8. [DOI: 10.1177/0954411912441325] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Muscle physiological cross-sectional area predicts the maximum capability of a muscle to generate isometric force. Biomechanical models often use estimates of individual muscle physiological cross-sectional area to partition internal forces among different muscles and predict joint forces and stability. In the spine literature, these physiological cross-sectional area values are generally obtained from imaging or cadaveric studies that have not accounted for a potential lengthened or shortened (and thus thinned or thickened, respectively) state of the muscles in question. Sarcomere length measurements can be used to normalize muscle lengths and correct for these length discrepancies. This article was designed to demonstrate potential effects of not accounting for instantaneous sarcomere length when calculating the physiological cross-sectional area of muscles of the spine region. Because some muscles of the spine region appear to be shortened and others lengthened in the neutral spine posture, both over- and under-estimations of physiological cross-sectional area are possible. Specifically, it is shown that the muscle physiological cross-sectional area could be over-estimated or under-estimated by as much as +36% (multifidus) and −21% (rectus abdominis), respectively. This differential error effect poses difficulties in accurately estimating individual muscle forces and subsequent spine forces and stability that result from biomechanical models incorporating physiological cross-sectional area data obtained in the absence of sarcomere length measurements. Future work is needed to measure the dynamic range of sarcomere lengths of all spinal muscles to ensure correct inputs to biomechanical models.
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Affiliation(s)
- Stephen HM Brown
- Department of Human Health and Nutritional Sciences, University of Guelph, Canada
| | - Michael E Gerling
- Department of Human Health and Nutritional Sciences, University of Guelph, Canada
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Co-activation alters the linear versus non-linear impression of the EMG–torque relationship of trunk muscles. J Biomech 2008; 41:491-7. [DOI: 10.1016/j.jbiomech.2007.10.015] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2007] [Revised: 10/24/2007] [Accepted: 10/29/2007] [Indexed: 11/17/2022]
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Staudenmann D, Potvin JR, Kingma I, Stegeman DF, van Dieën JH. Effects of EMG processing on biomechanical models of muscle joint systems: Sensitivity of trunk muscle moments, spinal forces, and stability. J Biomech 2007; 40:900-9. [PMID: 16765965 DOI: 10.1016/j.jbiomech.2006.03.021] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2005] [Accepted: 03/07/2006] [Indexed: 11/19/2022]
Abstract
Biomechanical models are in use to estimate parameters such as contact forces and stability at various joints. In one class of these models, surface electromyography (EMG) is used to address the problem of mechanical indeterminacy such that individual muscle activation patterns are accounted for. Unfortunately, because of the stochastical properties of EMG signals, EMG based estimates of muscle force suffer from substantial estimation errors. Recent studies have shown that improvements in muscle force estimation can be achieved through adequate EMG processing, specifically whitening and high-pass (HP) filtering of the signals. The aim of this paper is to determine the effect of such processing on outcomes of a biomechanical model of the lumbosacral joint and surrounding musculature. Goodness of fit of estimated muscle moments to net moments and also estimated joint stability significantly increased with increasing cut-off frequencies in HP filtering, whereas no effect on joint contact forces was found. Whitening resulted in moment estimations comparable to those obtained from optimal HP filtering with cut-off frequencies over 250 Hz. Moreover, compared to HP filtering, whitening led to a further increase in estimated joint-stability. Based on theoretical models and on our experimental results, we hypothesize that the processing leads to an increase in pick-up area. This then would explain the improvements from a better balance between deep and superficial motor unit contributions to the signal.
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Affiliation(s)
- Didier Staudenmann
- Institute for Fundamental and Clinical Human Movement Sciences, Faculty of Human Movement Sciences, Vrije Universiteit, Amsterdam, The Netherlands
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Hansen L, de Zee M, Rasmussen J, Andersen TB, Wong C, Simonsen EB. Anatomy and biomechanics of the back muscles in the lumbar spine with reference to biomechanical modeling. Spine (Phila Pa 1976) 2006; 31:1888-99. [PMID: 16924205 DOI: 10.1097/01.brs.0000229232.66090.58] [Citation(s) in RCA: 139] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
STUDY DESIGN This article describes the development of a musculoskeletal model of the human lumbar spine with focus on back muscles. It includes data from literature in a structured form. OBJECTIVE To review the anatomy and biomechanics of the back muscles related to the lumbar spine with relevance for biomechanical modeling. SUMMARY OF BACKGROUND DATA To reduce complexity, muscle units have been incorporated in an abridged manner, reducing their actions more or less to a single force equivalent. In early models of the lumbar spine, this may have been a necessary step to reduce complexity and, thereby, calculation time. The muscles of the spine are well described in the literature, but mainly qualitatively. Most of the literature provides a description of the structures without precise data of fiber length, muscle length, cross-sectional areas, moment arms, forces, etc. The predicted output of musculoskeletal models is very much dependent on the input parameters. The information needed to improve models consists of better approximations of the attachments to the vertebrae, and more precise data. METHOD Review of literature. RESULTS The predicted output of musculoskeletal models is very much dependent on the input parameters. Moderate changes in the assumed muscle line-of-action (i.e., moment arm) could substantially alter the magnitudes of predicted muscle and spinal forces, while the choice of optimization formulation is less sensitive. CONCLUSIONS Input parameters, moment arms, as well as physiologic cross-sectional areas have a profound effect on the predicted muscle forces. Therefore, it is important to choose the values for moment arm and physiologic cross-sectional area carefully because they are essential input parameters to biomechanical models.
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Affiliation(s)
- Lone Hansen
- Institute of Medical Anatomy, Biomech. and Motor Control, University of Copenhagen, Denmark.
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Arjmand N, Shirazi-Adl A. Model and in vivo studies on human trunk load partitioning and stability in isometric forward flexions. J Biomech 2006; 39:510-21. [PMID: 16389091 DOI: 10.1016/j.jbiomech.2004.11.030] [Citation(s) in RCA: 115] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2004] [Accepted: 11/29/2004] [Indexed: 11/21/2022]
Abstract
To resolve the trunk redundancy to determine muscle forces, spinal loads, and stability margin in isometric forward flexion tasks, combined in vivo-numerical model studies was undertaken. It was hypothesized that the passive resistance of both the ligamentous spine and the trunk musculature plays a crucial role in equilibrium and stability of the system. Fifteen healthy males performed free isometric trunk flexions of approximately 40 degrees and approximately 65 degrees +/- loads in hands while kinematics by skin markers and EMG activity of trunk muscles by surface electrodes were measured. A novel kinematics-based approach along with a nonlinear finite element model were iteratively used to calculate muscle forces and internal loads under prescribed measured postures and loads considered in vivo. Stability margin was investigated using nonlinear, linear buckling, and perturbation analyses under various postures, loads and alterations in ligamentous stiffness. Flexion postures significantly increased activity in extensor muscles when compared with standing postures while no significant change was detected in between flexed postures. Compression at the L5-S1 substantially increased from 570 and 771 N in upright posture, respectively, for +/-180 N, to 1912 and 3308 N at approximately 40 degrees flexion, and furthermore to 2332 and 3850 N at approximately 65 degrees flexion. Passive ligamentous/muscle components resisted up to 77% of the net moment. In flexion postures, the spinal stability substantially improved due both to greater passive stiffness and extensor muscle activities so that, under 180 N, no muscle stiffness was required to maintain stability. The co-activity of abdominal muscles and the muscle stiffness were of lesser concern to maintain stability in forward flexion tasks as compared with upright tasks. An injury to the passive system, on one hand, required a substantial compensatory increase in active muscle forces which further increased passive loads and, hence, the risk of injury and fatigue. On the other hand, it deteriorated the system stability which in turn could require greater additional muscle activation. This chain of events would place the entire trunk active-passive system at higher risks of injury, fatigue and instability.
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Affiliation(s)
- N Arjmand
- Division of Applied Mechanics, Department of Mechanical Engineering, Ecole Polytechnique de Montreal, P.O. Box 6079, Station 'centre-ville', Montréal, Qué., Canada H3C 3A7
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Abstract
STUDY DESIGN In vivo measurements and model studies are combined to investigate the role of lumbar posture in static lifting tasks. OBJECTIVES Identification of the role of changes in the lumbar posture on muscle forces, internal loads, and system stability in static lifting tasks with and without load in hands. SUMMARY OF BACKGROUND DATA Despite the recognition of the causal role of lifting in spinal injuries, the advantages of preservation or flattening of the lumbar lordosis while performing lifting tasks is not yet clear. METHODS Kinematics of the spine and surface EMG activity of selected muscles were measured in 15 healthy subjects under different forward trunk flexion angles and load cases. Apart from the freestyle lumbar posture, subjects were instructed to take either lordotic or kyphotic posture as well. A kinematics-based method along with a nonlinear finite element model were interactively used to compute muscle forces, internal loads and system stability margin under postures, and loads considered in in vivo investigations. RESULTS.: In comparison with the kyphotic postures, the lordotic postures increased the pelvic rotation, active component of extensor muscle forces, segmental axial compression and shear forces at L5-S1, and spinal stability margin while decreasing the passive muscle forces and segmental flexion moments. CONCLUSION Alterations in the lumbar lordosis in lifting resulted in significant changes in the muscle forces and internal spinal loads. Spinal shear forces at different segmental levels were influenced by changes in both the disc inclinations and extensor muscle lines of action as the posture altered. Considering internal spinal loads and active-passive muscle forces, the current study supports the freestyle posture or a posture with moderate flexion as the posture of choice in static lifting tasks.
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Affiliation(s)
- Navid Arjmand
- Department of Mechanical Engineering, Ecole Polytechnique Montréal, Québec, Canada
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El-Rich M, Shirazi-Adl A. Effect of load position on muscle forces, internal loads and stability of the human spine in upright postures. Comput Methods Biomech Biomed Engin 2005; 8:359-68. [PMID: 16393873 DOI: 10.1080/10255840500445630] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
A novel kinematics-based approach coupled with a non-linear finite element model was used to investigate the effect of changes in the load position and posture on muscle activity, internal loads and stability margin of the human spine in upright standing postures. In addition to 397 N gravity, external loads of 195 and 380 N were considered at different lever arms and heights. Muscle forces, internal loads and stability margin substantially increased as loads displaced anteriorly away from the body. Under same load magnitude and location, adopting a kyphotic posture as compared with a lordotic one increased muscle forces, internal loads and stability margin. An increase in the height of a load held at a fixed lever arm substantially diminished system stability thus requiring additional muscle activations to maintain the same margin of stability. Results suggest the importance of the load position and lumbar posture in spinal biomechanics during various manual material handling operations.
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Affiliation(s)
- M El-Rich
- Ecole Polytechnique, Department of Mechanical Engineering, Montréal, Qué., Canada
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11
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Stokes IAF. Relationships of EMG to effort in the trunk under isometric conditions: force-increasing and decreasing effects and temporal delays. Clin Biomech (Bristol, Avon) 2005; 20:9-15. [PMID: 15567531 DOI: 10.1016/j.clinbiomech.2004.08.010] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/27/2004] [Accepted: 08/27/2004] [Indexed: 02/07/2023]
Abstract
BACKGROUND Electromyograms are used in increasingly sophisticated biomechanical analyses to estimate forces within the trunk to prevent and evaluate painful spinal conditions. However, even under nominally isometric conditions the relationship between EMG and effort is complex. This study quantified influences of pulling direction, increasing versus decreasing effort and electromechanical delay on the EMG/effort relationships for principal lower trunk muscle groups in isometric pulling tasks, to determine whether the observed differences between increasing versus decreasing effort relationships were consistent with electromechanical delay or activation differences. METHODS Twenty-three healthy subjects (15 male, 8 female; mean age 32 years; mean bodymass 74.5 kg) each stood in an apparatus to stabilize the pelvis and performed ramped isometric efforts with a harness around the thorax connected to each of a series of five anchor points on the wall, for angles of pull at each 45 degrees increment from 0 degrees to 180 degrees to the anterior direction. A load cell recorded the generated force for a 5 s timed increase up to a voluntary maximum, a 1s 'dwell', and a 5 s relaxation back to zero effort. EMG signals were recorded via electrodes (surface, except indwelling for multifidus) from right and left rectus abdominis, internal and external obliques, longissimus, iliocostalis and L2 and L4 level multifidus. EMG signals were rectified with a 250 ms root-mean-square moving average filter. Effort-increasing and effort-decreasing sections of recordings were analyzed separately. FINDINGS The EMG/effort relationship had a statistically significantly greater gradient as the effort was increasing than when decreasing for 28 of 70 muscle-angle permutations. This difference in gradient was found to explain a significant part of the apparent lag between effort generated and EMG signal that averaged between 261 and 658 ms before and between 31 and 196 ms for different muscles after the slope difference was taken into account. INTERPRETATION The findings were consistent with the notion that the motor unit recruitment differs in increasing versus decreasing isometric efforts, probably because of a small stretching of the muscle as its tension increases. The residual temporal delay was thought to represent electromechanical delay.
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Affiliation(s)
- Ian A F Stokes
- Department of Orthopaedics and Rehabilitation, University of Vermont, Stafford Hall 434, Burlington, VT 05405-0084, USA.
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El-Rich M, Shirazi-Adl A, Arjmand N. Muscle activity, internal loads, and stability of the human spine in standing postures: combined model and in vivo studies. Spine (Phila Pa 1976) 2004; 29:2633-42. [PMID: 15564912 DOI: 10.1097/01.brs.0000146463.05288.0e] [Citation(s) in RCA: 108] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
STUDY DESIGN The load in active and passive spinal components as well as the stability margin in standing postures +/- load in hands are studied using both computational model and in vivo studies. OBJECTIVE To investigate muscle activity, spinal loads, and system stability in standing postures. SUMMARY OF BACKGROUND DATA Study of the human trunk yields a redundant system, the satisfactory solution of which remains yet to be done. Existing biomechanical models are often oversimplified or attempt to solve the problem by equilibrium of loads at only one cross section along the spine. METHODS In vivo measurements are performed to obtain kinematics (by skin markers) as input data into model and EMG activity (by surface electrodes) for validation of predictions. A thoracolumbar model, while accounting for nonlinear ligamentous properties and trunk musculature, solved the redundant active-passive system by a novel kinematics-based approach that used both the posture and gravity/external loads as input data. In both studies, neutral standing posture was considered with weights up to 380 N held in hands with arms extended close to the body either in front or on sides. RESULTS Predicted muscle forces were in satisfactory agreement with measured EMG activities. The activity in extensor muscles significantly increased with the load magnitude when held in front, a trend that disappeared as loads were held on sides. Abdominal muscles remained relatively silent. Large compression forces of approximately 2000 N were computed in lower lumbar levels when 380 N was held in front. Coactivity in abdominal muscles markedly increased internal loads and stability margin. CONCLUSION A tradeoff exists between lower loads in passive tissues (i.e., tissue risk of failure) and higher stability margins as both increase with greater muscle coactivation. Greater muscle activity observed under load held in front did not necessarily yield larger stability margin as the position of load appeared to play an important role as well. The strength of the proposed model is in realistic consideration of both passive-active structures under postures and gravity/external loads, yielding results that satisfy kinematics, equilibrium, and stability requirements in all directions along the spine.
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Affiliation(s)
- Marwan El-Rich
- Department of Mechanical Engineering, Ecole Polytechnique, Montréal, Québec, Canada
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Sparto PJ, Parnianpour M. Generalizability of trunk muscle EMG and spinal forces. IEEE ENGINEERING IN MEDICINE AND BIOLOGY MAGAZINE : THE QUARTERLY MAGAZINE OF THE ENGINEERING IN MEDICINE & BIOLOGY SOCIETY 2001; 20:72-81. [PMID: 11838261 DOI: 10.1109/51.982278] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
The generalizability of trunk muscle EMG and spinal loading estimates obtained from an EMG-assisted biomechanical model was assessed over three occasions and three repetitions. The greatest sources of variability consisted of the intersubject differences and the interaction between subject and occasion. The ID (reliability coefficient) was less for trunk muscle activity compared with estimates of anteroposterior shear force, compression force, and gain computed from the biomechanical model. In order to obtain an ID of 0.8, we recommend five testing occasions for submaximal EMG measurements and three testing occasions for biomechanical estimates. Reproducible estimates of maximal trunk extensor EMG could not be obtained within five testing occasions and five repetitions. Although many recruitment patterns could cause the same extension torque output, their net effect on internal loading seems to be less variable than the underlying measurements.
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Affiliation(s)
- P J Sparto
- Department of Physical Therapy and Otolaryngology, University of Pittsburgh, USA.
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Marras WS, Davis KG, Maronitis AB. A non-MVC EMG normalization technique for the trunk musculature: Part 2. Validation and use to predict spinal loads. J Electromyogr Kinesiol 2001; 11:11-8. [PMID: 11166604 DOI: 10.1016/s1050-6411(00)00040-7] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Estimates of the amount of force exerted by a muscle using electromyography (EMG) rely partially upon the accuracy of the reference point used in the normalization technique. Accurate representations of muscle activities are essential for use in EMG-driven spinal loading models. The expected maximum contraction (EMC) normalization method was evaluated to explore whether it could be used to assess individuals who are not capable of performing a maximum exertion such as a person with a low back injury. Hence, this study evaluated the utility of an EMG normalization method (Marras and Davis, A non-MVC EMG normalization technique, Part 1, method development. Journal of Electromyography and Kinesiology 2000) that draws upon sub-maximal exertions to determine the reference points needed for normalization of the muscle activities. The EMC normalization technique was compared to traditional MVC-based EMG normalization by evaluating the spinal loads for 20 subjects (10 males and 10 females) performing dynamic lifts. The spinal loads (estimated via an EMG-assisted model) for the two normalization techniques were very similar with differences being <8%. The model performance variables indicated that both normalization techniques performed well (r(2)>0.9 and average error below 6%) with only the muscle gain being affected by normalization method as a result in different reference points. Based on these results, the proposed normalization technique was considered to be a viable method for EMG normalization and for use in EMG-assisted models. This technique should permit the quantitative evaluation of muscle activity for subjects unable to produce maximum exertions.
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Affiliation(s)
- W S Marras
- The Biodynamics Laboratory, The Ohio State University, 210 Baker Systems, 1971 Neil Avenue, Columbus OH 43210, USA.
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Sparto PJ, Parnianpour M. Estimation of trunk muscle forces and spinal loads during fatiguing repetitive trunk exertions. Spine (Phila Pa 1976) 1998; 23:2563-73. [PMID: 9854755 DOI: 10.1097/00007632-199812010-00011] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
STUDY DESIGN The effects of human trunk extensor muscle fatigue on the estimated trunk muscle forces and spinal loading were investigated during the performance of repetitive dynamic trunk extension. OBJECTIVE To evaluate if alterations in the trunk muscle recruitment patterns resulted in a greater estimated active loading of the spine and, in turn, an increased risk of injury. SUMMARY OF BACKGROUND DATA Epidemiologic studies highlight the increased risk of low back injury during repetitive lifting, implicating fatigue of muscles and/or passive tissues as causes of such injury. Increased trunk muscle activity or altered recruitment patterns resulting from fatigue in the primary trunk extensor muscles may indicate an increase in the active loading of the spine, which could contribute to an increased risk of injury. METHODS Sixteen healthy study participants performed repetitive isokinetic trunk extension endurance tests at two load levels and two repetition rates, while their net muscular torque output and trunk muscular activity were measured. During each exertion, trunk torque, position, and velocity were controlled, so that any change in muscle activity could be attributed to fatigue. An electromyography-assisted model, adapted to accommodate the decline in maximum muscular tension generation resulting from fatigue, was used to estimate the 10 trunk muscle forces and spinal loading. Linear regression was used to quantify the rate of change in muscle force and spinal loading resulting from fatigue, while analysis of variance was used to determine if the rate of change was dependent on the task conditions (load and repetition rate). RESULTS Significant elevations were estimated for the latissimus dorsi and external oblique muscle forces in more than 70% of the endurance tests, whereas significant reductions in the erector spinae muscle force were predicted in 75% of the trials. The magnitude of the range of change of the erector spinae and latissimus dorsi muscle forces was dependent on the load level and repetition rate. The reduction in erector spinae forces offset the augmented force in the other muscles, because the net changes in compression and lateral shear forces on the spine were not significant, and the anteroposterior shear was reduced. CONCLUSION The results of the study do not suggest that an increase in the muscular loading of the spine occurs as a result of changing trunk muscular recruitment patterns. Therefore, future studies should focus on injury mechanisms that may occur as a result of a change in the viscoelastic passive tissue responses, muscular insufficiency, or a decline in neuromuscular control and coordination.
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Affiliation(s)
- P J Sparto
- Biomedical Engineering Center, Ohio State University, Columbus, USA
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