Longitudinal alterations of pulmonary.VO2 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 (VO2) in response to moderate-intensity cycling on three occasions within 15 months in competitive youth cyclists. Furthermore, the muscle Delta deoxy[heme] on-kinetics and the Delta deoxy[heme]-to-VO2 ratio were modeled to examine possible mechanistic basis regulating pulmonary. VO2 on-kinetics. Methods: Eleven cyclists (initial age, 14.3 +/- 1.6 y; peak. VO2, 62.2 +/- 4.5 mL.min(-1).kg(-1)) with a training history of 2-5 years and a training volume of similar to 10 h per week participated in this investigation.. VO2 and Delta deoxy[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 Delta deoxy[heme]-to-. VO2 ratio was calculated for each participant. One-way repeated-measures ANOVA was used to assess e ects of time on the dependent variables of the responses. Results: The VO2 time constant remained unchanged between the first (similar to 24 s) and second visit (similar to 22 s, P > 0.05), whereas it was significantly improved through the third visit (similar to 13 s, P = 0.006-0.013). No significant effects of time were revealed for the parameter estimates of the Delta deoxy[heme] response ( P > 0.05). A significant Delta deoxy[heme]-to-VO2 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. VO2 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 tp and the Delta deoxy[heme]-to-VO2 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. VO2 time constant.