Timing of muscle activation of the lower limbs can be modulated to maintain a constant pedaling cadence |
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| Authors: | David M Rouffet Guillaume Mornieux Karim Zameziati Alain Belli Christophe A Hautier |
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| Institution: | 1. Université de Lyon, F-69622, Lyon, France – Université Lyon 1, Villeurbanne – EA 647, Centre de Recherche et d’Innovation sur le Sport;2. Centre for Ageing, Rehabilitation, Exercise and Sport, Victoria University, Melbourne, Australia;3. Universität Freiburg, Germany, Institut für Sport und Sportwissenschaft;4. Département STAPS – Université de Saint Etienne, France, Unité PPEH;1. Orthopaedic and Traumatology Department, Dubrovnik County Hospital, Dubrovnik, Croatia;2. Poliklinika Marin Med, Dubrovnik, Croatia;3. Dubrovnik Medical High School, Dubrovnik, Croatia;2. Delaware Rehabilitation Institute, University of Delaware, Newark, DE 19716, USA;3. Department of Mechanical Engineering, University of Delaware, Newark, DE 19716, USA;4. School of Kinesiology, University of Michigan, USA;6. Department of Physical Therapy, University of Delaware, Newark, DE 19716, USA;1. Department of Neurology, Christian Doppler Klinik, Paracelsus Medical University, Salzburg, Austria;2. Department of Neurology, Franz Tappeiner Hospital, Merano, Italy;3. Department of Mathematics, Paris Lodron University of Salzburg, Austria;4. Department of Neurological and Movement Sciences. Section of Clinical Neurology, University of Verona, Verona, Italy;5. Department of Neurology, Saarland University Medical Center, Homburg, Germany;6. Department of Physiology, Medical University of Graz, Graz, Austria;7. Spinal Cord Injury and Tissue Regeneration Center, Paracelsus Medical University, Salzburg, Austria;1. Center for Mobility and Rehabilitation Engineering Research, Kessler Foundation, West Orange, NJ, USA;2. Biomechanics/Sports Medicine Lab, Department of Kinesiology, Recreation and Sport Studies, The University of Tennessee, Knoxville, TN, USA |
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| Abstract: | This study investigated changes in muscle activity when subjects are asked to maintain a constant cadence during an unloaded condition. Eleven subjects pedaled for five loaded conditions (220 W, 190 W, 160 W, 130 W, 100 W) and one unloaded condition at 80 rpm. Electromyographic (EMG) activity of six lower limb muscles, pedal forces and oxygen consumption were calculated for every condition. Muscle activity was defined by timing (EMG onset and offset) and level (integrated values of EMGrms calculated between EMG onset and EMG offset) of activation, while horizontal and vertical impulses were computed to characterize pedal forces. Muscle activity, pedal forces and oxygen consumption variables measured during the unloaded condition were compared with those extrapolated to 0 W from the loaded conditions, assuming a linear relationship. The muscle activity was changed during unloaded condition: EMG onset and/or offset of rectus femoris, biceps femoris, vastus medialis, and gluteus maximus muscles were delayed (p < 0.05); iEMGrms values of rectus femoris, biceps femoris, gastrocnemius medialis and tibialis anterior muscles were higher than those extrapolated to 0 W (p < 0.05). Vertical impulse over the extension phase was lower (p < 0.05) while backward horizontal impulse was higher (p < 0.05) during unloaded condition than those extrapolated to 0 W. Oxygen consumptions were higher during unloaded condition than extrapolated to 0W (750 ± 147 vs. 529 ± 297 mLO2.min?1; p < 0.05). Timing of activation of rectus femoris and biceps femoris was dramatically modified to optimize pedal forces and maintain a constant cadence, while systematic changes in the activation level of the bi-articular muscles induced a relative increase in metabolic expenditure when pedaling during an unloaded condition. |
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