title: Changes in muscle coordination and power output during sprint cycling.
abstract: This study investigated the changes in muscle coordination associated to power output decrease during a 30-s isokinetic (120rpm) cycling sprint. Modifications in EMG amplitude and onset/offset were investigated from eight muscles [gluteus maximus (EMGGMAX), vastus lateralis and medialis obliquus (EMGVAS), medial and lateral gastrocnemius (EMGGAS), rectus femoris (EMGRF), biceps femoris and semitendinosus (EMGHAM)]. Changes in co-activation of four muscle pairs (CAIGMAX/GAS, CAIVAS/GAS, CAIVAS/HAM and CAIGMAX/RF) were also calculated. Substantial power reduction (60±6%) was accompanied by a decrease in EMG amplitude for all muscles other than HAM, with the greatest deficit identified for EMGRF (31±16%) and EMGGAS (20±14%). GASonset, HAMonset and GMAXonset shifted later in the pedalling cycle and the EMG offsets of all muscles (except GASoffset) shifted earlier as the sprint progressed (P<0.05). At the end of the sprint, CAIVAS/GAS and CAIGMAX/GAS were reduced by 48±10% and 43±12%, respectively. Our results show that substantial power reduction during fatiguing sprint cycling is accompanied by marked reductions in the EMG activity of bi-articular GAS and RF and co-activation level between GAS and main power producer muscles (GMAX and VAS). The observed changes in RF and GAS EMG activity are likely to result in a redistribution of the joint powers and alterations in the orientation of the pedal forces.
authors.affiliation: Institute of Sport, Exercise and Active Living (ISEAL), Victoria University, PO Box 14428, Melbourne, VIC 8001, Australia.
authors.forename: Steven J
authors.initials: SJ
authors.lastname: O'Bryan
authors.affiliation: Department of Biomechanics and Performance Analysis, Australian Institute of Sport, PO Box 176, Belconnen, ACT 2616, Australia.
authors.forename: Nicholas A T
authors.initials: NA
authors.lastname: Brown
authors.affiliation: Institute of Sport, Exercise and Active Living (ISEAL), Victoria University, PO Box 14428, Melbourne, VIC 8001, Australia; Institut national du sport du Québec, 1000, avenue Émile-Journault - bureau 1.72, Montréal, Qc H2M 2E7, Canada.
authors.forename: François
authors.initials: F
authors.lastname: Billaut
authors.affiliation: Institute of Sport, Exercise and Active Living (ISEAL), Victoria University, PO Box 14428, Melbourne, VIC 8001, Australia; Department of Biomechanics and Performance Analysis, Australian Institute of Sport, PO Box 176, Belconnen, ACT 2616, Australia. Electronic address: david.rouffet@vu.edu.au.
authors.forename: David M
authors.initials: DM
authors.lastname: Rouffet
mesh_terms: D000328:Adult; D001642:Bicycling / Q000502:physiology*; D004576:Electromyography; D006801:Humans; D007866:Leg / Q000502:physiology; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology*; D013997:Time Factors; D055815:Young Adult
keywords: Bi-articular muscles; Co-activation; EMG; Fatigue; Muscle activation; Power transfer