Selective activation of lower leg muscles during maximum voluntary isometric contractions |
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| Affiliation: | 1. Biomechanics Laboratory, Institute of Sport and Movement Sciences, University Duisburg-Essen, Gladbecker Str. 182, 45141 Essen, Germany;2. Discipline of Podiatry and Sport and Exercise Medicine Research Centre, School of Allied Health, La Trobe University, Bundoora, VIC 3086, Australia;3. Department of Allied Health, Melbourne Health, 300 Grattan St, Parkville, VIC 3050, Australia;1. AO Research Institute Davos, Davos, Switzerland;2. Catholic Clinic Mainz, Department of Foot and Ankle Surgery, Mainz, Germany;3. Friedrich-Schiller University Jena, University Hospital Jena, Department of Trauma, Hand and Reconstructive Surgery, Jena, Germany;1. Department of Physical Therapy, Faculty of Health and Welfare, Prefectural University of Hiroshima, 1–1 Gakuen-cho, Mihara-shi, Hiroshima 723-0053, Japan;2. Graduate School of Comprehensive Scientific Research, Prefectural University of Hiroshima, 1–1 Gakuen-cho, Mihara-shi, Hiroshima 723-0053, Japan;1. Faculty of Health, Education and Life Sciences, Birmingham City University, Birmingham, United Kingdom;2. Department of Kinesiology, University of San Francisco, CA, United States;3. School of Sport Science & Physical Activity, University of Bedfordshire, Bedford, United Kingdom;4. School of Life and Medical Sciences, University of Hertfordshire, Hatfield, United Kingdom |
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| Abstract: | The pronators and supinators play a key role in the medio-lateral stability of the ankle joint complex (i.e. talo-crural and subtalar joints). We hypothesized that each shank muscle has a specific activation pattern determined by its anatomical course around the axes of the subtalar and talo-crural joints. A secondary objective was to examine the effect of foot posture on these activation patterns. Forty-nine young adults (25 normal-arched feet, 24 flat-arched feet) performed maximum voluntary isometric contractions against manual resistance in four movement directions: plantarflexion (PF), dorsiflexion (DF), pronation (PRO) and supination (SUP). Electromyographic activity was recorded from tibialis posterior (TP) and peroneus longus (PL) with intramuscular electrodes, and gastrocnemius medialis (GM) and tibialis anterior (TA) with surface electrodes. When compared to their agonist function, all muscles were co-activated at significantly lower levels in their synergistic function (GM: 23% during SUP, TA: 72% during SUP; TP: 42% during PF, PL: 52% during PF) (p < 0.001). A significant interaction between foot posture and contraction type was evident for TA. During isometric contractions, the electromyographic activity of the shank muscles is geared to their biomechanical advantage according to their position relative to the subtalar and talo-crural joint axes. |
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| Keywords: | Muscles Electromyography Joint axis Agonist Synergist Foot posture |
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