Changes in muscle coordination and power output during sprint cycling

•Power deficit is accompanied by significant alterations in muscle coordination.•Large reductions in the EMG activity of RF and GAS muscles are observed during 30-s cycling sprint.•Co-activation between GAS and proximal mono-articular muscles are dramatically reduced.•Co-activation analysis complements information provided by biomechanical models.•Coordination is affected by central/peripheral fatigue or change in movement strategy.

This study investigated the changes in muscle coordination associated to power output decrease during a 30-s isokinetic (120 rpm) 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.