Characterization of performance fatigability during a self-paced exercise.J Appl Physiol (1985) 2019JA
Pacing during a high-intensity cycling time trial (TT) appears to prevent premature task failure, but the performance fatigability during a self-paced exercise is currently unknown. Therefore, the current study characterized the time-course of performance fatigability during a 4-km TT. Eleven male cyclists performed three separated TTs in a crossover counterbalanced design. The TTs lasted until the end of the fast-start (FS, 600 ± 205 m), even-pace (EP, 3600 ± 190 m) and end-spurt (ES, 4000 m) phases. Performance fatigability was characterized by using isometric maximal voluntary contractions (IMVC), while the muscle activation [i.e., voluntary activation (VA)] and contractile function of knee extensors [i.g., peak torque of potentiated twitches (TwPt)] were evaluated using electrically-evoked contractions performed (PRE) and 1 min after (POST) each specific part of the trial. Gas exchange, power output (PO) and electromyographic activity (EMG) were also recorded. EMG/PO showed an abrupt increase followed by a continuous decrease towards the end of FS resulting in a drop on IMVC (-12%), VA (-8%) and TwPt (-23%). EMG/PO was stable during EP, with no additional drop on IMVC, VA and TwPt (-12%, -6% and -22%, respectively). EMG/PO increased abruptly during the ES, but there was no change on IMVC, VA and TwPt (-13%, -8% and -26%, respectively). These findings demonstrate that the performance fatigability during a self-paced exercise is characterized by a large drop on contractile function and muscle activation at beginning of the trial (i.e., FS), without additional change during the middle and end phases (i.e., EP and ES).