Changes in muscle coordination and power output during sprint cycling

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 (EMG_GMAX), vastus lateralis and medialis obliquus (EMG_VAS), medial and lateral gastrocnemius (EMG_GAS), rectus femoris (EMG_RF), biceps femoris and semitendinosus (EMG_HAM)]. Changes in co-activation of four muscle pairs (CAI_GMAX/GAS, CAI_VAS/GAS, CAI_VAS/HAM and CAI_GMAX/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 EMG_RF (31±16%) and EMG_GAS (20±14%). GAS_onset, HAM_onset and GMAX_onset shifted later in the pedalling cycle and the EMG offsets of all muscles (except GAS_offset) shifted earlier as the sprint progressed (P<0.05). At the end of the sprint, CAI_VAS/GAS and CAI_GMAX/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.