The blood serum metabolome profile after different phases of a 4-km cycling time trial: Secondary analysis of a randomized controlled trial

Abstract

It has been assumed that exercise intensity variation throughout a cycling time trial (TT) occurs in alignment of various metabolic changes to prevent premature task failure. However, this assumption is based on target metabolite responses, which limits our understanding of the complex interconnection of metabolic responses during exercise. The current study characterized the metabolomic profile, an untargeted metabolic analysis, after specific phases of a cycling 4-km TT. Eleven male cyclists performed three separated TTs in a crossover counterbalanced design, which were interrupted at the end of the fast-start (FS, 600 ± 205 m), even-pace (EP, 3600 ± 190 m), or end-spurt (ES, 4000 m) phases. Blood samples were taken before any exercise and 5 min after exercise cessation, and the metabolomic profile characterization was performed using Nuclear Magnetic Resonance metabolomics. Power output (PO) was also continually recorded. There were higher PO values during the FS and ES compared to the EP (all p < 0.05), which were accompanied by distinct metabolomic profiles. FS showed high metabolite expression in TCA cycle and its related pathways (e.g., glutamate, citric acid, and valine metabolism); whereas, the EP elicited changes associated with antioxidant effects and oxygen delivery adjustment. Finally, ES was related to pathways involved in NAD turnover and serotonin metabolism. These findings suggest that the specific phases of a cycling TT are accompanied by distinct metabolomic profiles, providing novel insights regarding the relevance of specific metabolic pathways on the process of exercise intensity regulation.

Keywords: bioenergetic; metabolism; nuclear magnetic resonance spectrometry; pacing; self‐paced exercise.

FIGURE 1

Schematic figure for the experimental sessions. The flow‐chart of an experimental session is represented on the left‐hand side panel. Briefly, before any exercise, venous blood samples were taken at complete rest, which was followed by a 5‐min cycling warm‐up at a PO of 150 W. Thereafter, on separated sessions, the participants cycled for different durations of a pre‐established PO based on the best 4‐km TT performance in the familiarization sessions. As shown in the bottom right panel, the schematic output from a participant is highlighted for the three experimental sessions in different colors and symbols. Thus, the participant replicated the same PO and pacing strategy up to the point which exercise was stopped (i.e., either FS or EP phases' sessions). During the exercise bouts, the anaerobic and aerobic bioenergetic pathways were estimated and the rating of perceived exertion (RPE) was recorded. Finally, 5 min post‐exercise, another venous blood sample was obtained and later processed in the nuclear magnetic resonance (NMR) to obtain the metabolites concentrations. PO, power output.

FIGURE 2

Variables measured at each 4‐km time trial phase. Panel (A) total power output produced in terms of the sum from aerobic (P_AER) and anaerobic (P_ANAE) metabolic power throughout each 4‐km time trial phase; Panel (B) RPE throughout each 4‐km time trial phase. Data presented as mean ± SD from each phase of the time trial, as follows: FS, EP and ES. * statistically different from the other phases (p < 0.05); Panel (C–E) the PLS‐DA, VIP of each metabolite that discriminate the differences between phases and EA)highlighting the main bioenergetics pathways that differentiates FS and EP phases; Panel (F–H), the PLS‐DA, VIP of each metabolite that discriminate the differences between phases and EA highlighting the main bioenergetics pathways that differentiates EP and ES phases; Panel (I–K) the PLS‐DA, VIP of each metabolite that discriminate the differences between phases and EA, highlighting the main bioenergetic pathways that differentiates FS and ES phases. RPE, rating of perceived exertion; FS, follows: fast‐start; EP, even‐pace; ES, end‐spurt; PLS‐DA, partial least square–discriminant analysis; VIP, variable importance in the projection; EA, enrichment analysis.