Long-Term Alterations in Pulmonary V˙O2 and Muscle Deoxygenation On-Kinetics During Heavy-Intensity Exercise in Competitive Youth Cyclists: A Cohort Study.

PURPOSE: The aim of this investigation was to assess alterations of pulmonary oxygen uptake (V˙O2) and muscle deoxygenation on-kinetics during heavy-intensity cycling in youth cyclists over a period of 15 months. METHODS: Eleven cyclists (initial age, 14.3 [1.6] y; peak V˙O2, 62.2 [4.5] mL·min-1·kg-1) visited the laboratory twice on 3 occasions within 15 months. Participants performed an incremental ramp exercise test and a constant workrate test within the heavy-intensity domain during the first visit and second visit, respectively. Subsequently, parameter estimates of the V˙O2 and muscle deoxygenation on-kinetics were determined with mono-exponential models. RESULTS: The V˙O2 phase II time constant decreased from occasion 1 (34 [4] s) to occasion 2 (30 [4] s, P = .005) and 3 (28 [4] s, P = .010). However, no significant alteration was observed between occasions 2 and 3 (P = .565). The V˙O2 slow component amplitude either expressed in absolute values (ie, L·min-1) or relative to end exercise V˙O2 (ie, %) showed no significant changes throughout the study (P = .972 and .996). Furthermore, the muscle deoxygenation on-kinetic mean response time showed no significant changes throughout the study (18 [8], 18 [3], and 16 [5] s for occasions 1, 2, and 3, respectively; P = .279). CONCLUSION: These results indicate proportional enhancements of local muscle oxygen distribution and utilization, which both contributed to the speeding of the V˙O2 on-kinetics herein.

Physiological Characteristics of Competitive Male Junior Cyclists Transitioning to the Under-23 Level: A Retrospective Comparative Study.

PURPOSE: The purpose of the current investigation was to retrospectively assess possible differences in physiological performance characteristics between junior cyclists signing a contract with an under-23 (U23) development team versus those failing to sign such a contract. METHODS: Twenty-five male junior cyclists (age: 18.1 [0.7] y, stature: 181.9 [6.0] cm, body mass: 69.1 [7.9] kg, peak oxygen uptake: 71.3 [6.2] mL·min-1·kg-1) were assigned to this investigation. Between September and October of the last year in the junior category, each cyclist performed a ramp incremental exercise test to determine certain physiological performance characteristics. Subsequently, participants were divided in 2 groups: (1) those signing a contract with a U23 development team (JUNIORU23) and (2) those failing to sign such a contract (JUNIORNON-U23). Unpaired t tests were used to assess possible between-groups differences in physiological performance characteristics. The level of statistical significance was set at P < .05 two tailed. RESULTS: No significant between-groups differences in submaximal (ie, gas exchange threshold, respiratory compensation point) and maximal physiological performance characteristics (ie, peak work rate, peak oxygen uptake) expressed in absolute values (ie, L·min-1, W) were observed (P > .05). However, significant between-groups differences were observed when physiological performance characteristics were expressed relative to the cyclists' body weights (P < .05). CONCLUSIONS: The current investigation showed that junior cyclists stepping up to a U23 development team might be retrospectively differentiated from junior cyclists not stepping up based on certain physiological performance characteristics, which might inform practitioners and/or federations working with young cyclists during the long-term athletic development process.

Longitudinal alterations of pulmonary V . O2 on-kinetics during moderate-intensity exercise in competitive youth cyclists are related to alterations in the balance between microvascular O2 distribution and muscular O2 utilization.

Purpose: The main purpose of the current study was to investigate the dynamic adjustment of pulmonary oxygen uptake ( V . O2) in response to moderate-intensity cycling on three occasions within 15 months in competitive youth cyclists. Furthermore, the muscle Δdeoxy[heme] on-kinetics and the Δdeoxy[heme]-to- V . O2 ratio were modeled to examine possible mechanistic basis regulating pulmonary V . O2 on-kinetics. Methods: Eleven cyclists (initial age, 14.3 ± 1.6 y; peak V . O2, 62.2 ± 4.5 mL.min-1.kg-1) with a training history of 2-5 years and a training volume of ~10 h per week participated in this investigation. V . O2 and Δdeoxy[heme] responses during workrate-transitions to moderate-intensity cycling were measured with breath-by-breath spirometry and near-infrared spectroscopy, respectively, and subsequently modeled with mono-exponential models to derive parameter estimates. Additionally, a normalized Δdeoxy[heme]-to- V . O2 ratio was calculated for each participant. One-way repeated-measures ANOVA was used to assess effects of time on the dependent variables of the responses. Results: The V . O2 time constant remained unchanged between the first (~24 s) and second visit (~22 s, P > 0.05), whereas it was significantly improved through the third visit (~13 s, P = 0.006-0.013). No significant effects of time were revealed for the parameter estimates of the Δdeoxy[heme] response (P > 0.05). A significant Δdeoxy[heme]-to- V . O2 ratio "overshoot" was evident on the first (1.09 ± 0.10, P = 0.006) and second (1.05 ± 0.09, P = 0.047), though not the third (0.97 ± 0.10, P > 0.05), occasion. These "overshoots" showed strong positive relationships with the V . O2 time constant during the first (r = 0.66, P = 0.028) and second visit (r = 0.76, P = 0.007). Further, strong positive relationships have been observed between the individual changes of the fundamental phase τp and the Δdeoxy[heme]-to- V . O2 ratio "overshoot" from occasion one to two (r = 0.70, P = 0.017), and two to three (r = 0.74, P = 0.009). Conclusion: This suggests that improvements in muscle oxygen provision and utilization capacity both occurred, and each may have contributed to enhancing the dynamic adjustment of the oxidative "machinery" in competitive youth cyclists. Furthermore, it indicates a strong link between an oxygen maldistribution within the tissue of interrogation and the V . O2 time constant.

Test-retest reliability of pulmonary oxygen uptake and muscle deoxygenation during moderate- and heavy-intensity cycling in youth elite-cyclists.

To establish the test-retest reliability of pulmonary oxygen uptake (V̇O2), muscle deoxygenation (deoxy[haem]) and tissue oxygen saturation (StO2) kinetics in youth elite-cyclists. From baseline pedalling, 15 youth cyclists completed 6-min step transitions to a moderate- and heavy-intensity work rate separated by 8 min of baseline cycling. The protocol was repeated after 1 h of passive rest. V̇O2 was measured breath-by-breath alongside deoxy[haem] and StO2 of the vastus lateralis by near-infrared spectroscopy. Reliability was assessed using 95% limits of agreement (LoA), the typical error (TE) and the intraclass correlation coefficient (ICC). During moderate- and heavy-intensity step cycling, TEs for the amplitude, time delay and time constant ranged between 3.5-21.9% and 3.9-12.1% for V̇O2 and between 6.6-13.7% and 3.5-10.4% for deoxy[haem], respectively. The 95% confidence interval for estimating the kinetic parameters significantly improved for ensemble-averaged transitions of V̇O2 (p < 0.01) but not for deoxy[haem]. For StO2, the TEs for the baseline, end-exercise and the rate of deoxygenation were 1.0-42.5% and 1.1-5.5% during moderate- and heavy-intensity exercise, respectively. The ICC ranged from 0.81 to 0.99 for all measures. Test-retest reliability data provide limits within which changes in V̇O2, deoxy[haem] and StO2 kinetics may be interpreted with confidence in youth athletes.