Decreasing the required lumbar extensor moment induces earlier onset of flexion relaxation |
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| Affiliation: | 1. Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, ON, Canada;2. Faculty of Medicine, Memorial University of Newfoundland, St John’s, NL, Canada;1. Departamento de Física, Universidad Nacional de La Plata, Argentina;2. Departamento de Matemática, Universidad Nacional de La Plata, Argentina;3. Fac. de C. Exactas-National University La Pampa Peru y Uruguay, Santa Rosa, La Pampa, Argentina;4. Consejo Nacional de Investigaciones Científicas y Tecnológicas, (IFLP-CCT-CONICET)-C. C. 727, 1900 La Plata, Argentina;5. SThAR - EPFL, Lausanne, Switzerland;1. Human Movement Biomechanics Research Group, Department of Movement Sciences, KU Leuven, Belgium;2. Research Group for Musculoskeletal Rehabilitation, Department of Rehabilitation Sciences, KU Leuven, Belgium;3. Division of Rheumatology, UZ Leuven, Belgium;4. Skeletal Biology and Engineering Research Center, Department of Development and Regeneration, KU Leuven, Belgium;1. School of Mechanical Engineering, The University of Adelaide, Spinal Research Group, Centre for Orthopaedic & Trauma Research, Adelaide Medical School, The University of Adelaide, Level 7, Adelaide Health and Medical Sciences Building, North Terrace, Adelaide, SA, Australia;2. School of Engineering, The University of Guelph, Thornbrough Building, 50 Stone Rd, Guelph, ON, Canada;3. School of Mechanical Engineering, The University of Adelaide, Floor/Room 2 33, Engineering South Building, Adelaide, SA 5005, Australia;4. The University of Adelaide, Emeritus Consultant Spinal Surgery, Royal Adelaide Hospital, 160 East Terrace, Adelaide, SA, Australia;5. Spinal Injuries Unit, Royal Adelaide Hospital, Spinal Research Group, Centre for Orthopaedic & Trauma Research, Adelaide Medical School, The University of Adelaide, Spinal Unit Administration, 5G 531, Royal Adelaide Hospital, Port Road Adelaide, SA, Australia;6. School of Human Kinetics, The University of Ottawa, Lees E260G, Ottawa, Canada;7. Centre for Orthopaedic & Trauma Research, Adelaide Medical School, The University of Adelaide, Level 7, Adelaide Health and Medical Sciences Building, North Terrace, Adelaide, SA, Australia;8. Spinal Research Group, Centre for Orthopaedic & Trauma Research, Adelaide Medical School, The University of Adelaide, School of Mechanical Engineering, The University of Adelaide, Level 7, Adelaide Health and Medical Sciences Building, North Terrace, Adelaide, SA, Australia;1. Bioengineering Research Group, School of Engineering, Cardiff University, CF24 3AA, UK;2. Faculty of Health and Social Sciences, Bournemouth University, UK |
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| Abstract: | Flexion relaxation (FR) is characterized by the lumbar erector spinae (LES) becoming myoelectrically silent near full trunk flexion. This study was designed to: (1) determine if decreasing the lumbar moment during flexion would induce FR to occur earlier; (2) characterize thoracic and abdominal muscle activity during FR. Ten male participants performed four trunk flexion/extension movement conditions; lumbar moment was altered by attaching 0, 5, 10, or 15 lb counterweights to the torso. Electromyography (EMG) was recorded from eight trunk muscles. Lumbar moment, lumbar flexion and trunk inclination angles were calculated at the critical point of LES inactivation (CPLES). Results demonstrated that counterweights decreased the lumbar moment and lumbar flexion angle at CPLES (p < 0.0001 and p = 0.0029, respectively); the hypothesis that FR occurs earlier when lumbar moment is reduced was accepted. The counterweights did not alter trunk inclination at CPLES (p = 0.1987); this is believed to result from an altered hip to spine flexion ratio when counterweights were attached. Lumbar multifidus demonstrated FR, similar to LES, while thoracic muscles remained active throughout flexion. Abdominal muscles activated at the same instant as CPLES, except in the 15 lb condition where abdominal muscles activated before CPLES resulting in a period of increased co-contraction. |
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| Keywords: | Flexion relaxation Multifidus Lumbar erector spinae Thoracic erector spinae Critical point Trunk inclination |
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