Characterization of performance fatigability during a self-paced exercise

Author(s)

Azevedo, Rafael de Almeida ^{[1, 2]} ; Cruz, Ramon ^[1] ; Couto, Patricia ^[1] ; Silva-Cavalcante, Marcos David ^{[1, 3]} ; Boari, Daniel ^[4] ; Lima-Silva, Adrian E. ^{[3, 5]} ; Millet, Guillaume Y. ^[2] ; Bertuzzi, Romulo ^[1]

Affiliation

^[1] Univ Sao Paulo, Sch Phys Educ & Sport, Endurance Performance Res Grp, Sao Paulo - Brazil

^[2] Univ Calgary, Fac Kinesiol, Human Performance Lab, Calgary, AB - Canada

^[3] Univ Fed Pernambuco, Acad Ctr Vitoria, Sport Sci Res Grp, Pernambuco - Brazil

^[4] Fed Univ ABC, Ctr Engn Modeling & Appl Social Sci, Sao Paulo - Brazil

^[5] Technol Fed Univ Parana, Human Performance Res Grp, Curitiba, Parana - Brazil

• Document type: Journal article
• Source: Journal of Applied Physiology; v. 127, n. 3, p. 838-846, SEP 2019.
• Web of Science Citations: 0

Abstract

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; 3,600 +/- 190 m), and end-spurt (ES; 4,000 m) phases. Performance fatigability was characterized by using isometric maximal voluntary contractions (IMVCs), whereas the muscle activation {[}i.e., voluntary activation (VA)] and contractile function of knee extensors {[}e.g., peak torque of potentiated twitches (TwPt)] were evaluated using electrically evoked contractions performed before and 1 min after 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 toward the end of FS, resulting in a drop in IMVC (- 12%), VA (-8%), and TwPt (-23%). EMG/PO was stable during EP, with no additional drop on IMVC, VA, or TwPt (-12%, -6%, and -22%, respectively). EMG/PO increased abruptly during the ES, but there was no change in IMVCs, VA, or TwPt (-13%, -8%, and -26%, respectively). These findings demonstrate that the performance fatigability during a self-paced exercise is characterized by a large drop in contractile function and muscle activation at the beginning of the trial (i.e., FS), without additional change during the middle and end phases (i.e., EP and ES). NEW \& NOTEWORTHY The time course of performance fatigability throughout a self-paced exercise is currently unknown. The results showed that a large amount of muscle activation and contractile function impairments are attained early on a self-paced exercise (first similar to 15% of the total time trial distance) and maintained throughout the test. This novel finding characterizes the performance fatigability from a contractile function and muscle activation perspective, which brings new insights for future studies focused on real-world exercise training and competition. (AU)

• FAPESP's process: 17/22053-0 - Pacing in cycling: a study about the neuromuscular fatigue and metabolic interface
• Grantee: Rômulo Cássio de Moraes Bertuzzi
• Support Opportunities: Regular Research Grants