Monitoring pulmonary V̇O2 on-kinetics during a 3-year period in youth elite-cyclists
Keywords:VO2 kinetics, endurance performance, youth athletes, oxidative phosphorylation, adolescent cyclists
Background: Pulmonary oxygen uptake (V̇O2) on-kinetics provide insights into the processes underlying the increase in O2 flux from ambient air to muscle mitochondria following the onset of exercise. Therefore, the V̇O2 on-kinetic response is related to the O2 debt and ultimately exercise tolerance (Poole and Jones, 2005: Comprehensive Physiology, 2(2), 933-996). A detrimental effect of aging (i.e. from childhood to adulthood) on the primary V̇O2 on-kinetic response and slow component has been shown consistently by a number of longitudinal and cross-sectional studies (for review see McNarry, 2019: Pediatric Exercise Science, 31(2), 175-183).
Purpose: Therefore, the purpose of this study was to investigate the effects of aging on pulmonary V̇O2 on-kinetics during moderate and heavy intensity exercise in youth elite-cyclists throughout a period of ~3 years.
Methods: Nine trained youth elite-cyclists visited the laboratory twice on three occasions within a period of ~3 years (Feb-2017, May-2018, Sep-2019). Anthropometric measures and a graded ramp-exercise test (GXT, 20 W.min-1) to determine peak oxygen uptake (V̇O2peak), maximal power (Wmax), ventilatory threshold (VT) and the intensity corresponding to 50% between VT and Wmax (Δ50%) were conducted during the first visit (see table 1 for participant characteristics). On a subsequent visit, participants performed two square-wave transitions from a 3-min baseline at 40 W to a work-rate corresponding to 90% VT (moderate intensity) and Δ50% (heavy intensity), respectively. All tests were conducted on the participants own road bikes mounted on a Cyclus 2 ergometer (RBM Electronics, Leipzig, Germany). Gas exchange and pulmonary ventilation were measured continuously during the GXT and breath-by-breath during the square-wave transitions with a portable gas analyser (MetaMax 3B, Cortex Biophysik, Leipzig, Germany). To determine V̇O2 kinetic parameters, breath-by-breath data were filtered, linearly interpolated at 1-second intervals and time aligned to the onset of exercise. To account for the cardio-dynamic phase the first 20 s of each square-wave transition were excluded from further analyses. The parameter estimates of the exponential primary phase (i.e. time constant (τ), amplitude) were resolved by least-squares regression (GraphPad Prism 8.4.3, GraphPad Software Inc., San Diego, CA, USA). The V̇O2 slow component evident during heavy intensity exercise was calculated as the difference between end-exercise V̇O2 and amplitude. A repeated measures ANOVA was used for statistical analyses. Tukey’s post-hoc test was used for multiple pairwise comparisons. The level of statistical significance was set at p < 0.05 two tailed for all tests.
Results: The parameter estimates of the primary phase V̇O2 response for both square-wave transitions throughout the study are shown in figure 1. During moderate and heavy intensity exercise, τ significantly improved (i.e. was reduced) over time (90% VT: F2,16 = 7.18, P = 0.006; Δ50%: F2,16 = 14.70, P < 0.001). As a result of the increased work rate during moderate and heavy intensity exercise, the amplitude significantly increased over time (90% VT: F2,16 = 27.40, P < 0.001; Δ50%: F2,16 = 23.41, P < 0.001). For multiple pairwise comparisons see figure 1. The V̇O2 slow component was not significantly affected by time (absolute: F2,16 = 3.34, P = 0.061, relative: F2,16 = 0.76, P = 0.456, see figure 2).
Discussion: The findings of this study are not in line with previous longitudinal and cross-sectional studies showing increases of the moderate and/or heavy intensity exercise primary phase τ and the V̇O2 slow component in untrained individuals with age (i.e. from childhood to adulthood). These previous findings suggest that aging (i.e. from childhood to adulthood) is related with a slowing and augmentation of the primary phase τ and the V̇O2 slow component, respectively and therefore reduces the potential for oxidative phosphorylation at the onset of exercise (for review see McNarry, 2019: Pediatric Exercise Science, 31(2), 175-183). In contrast, the results of the current investigation suggest that regularly performed endurance training of elite youth-cyclists augments the potential for oxidative phosphorylation and reduces the impairments observed with aging. However, these results must be interpreted with caution due to the lack of a control group.
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