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.

Reproducibility of peak moment for isometric and isokinetic knee extension exercise.

BACKGROUND: Accurate measurements of muscular performance are important for diagnostics, for example during rehabilitation after traumatic injuries but also in competitive sports. For these purposes, dynamometric devices are widely used and considered the gold standard for muscle strength testing. However, few previous studies have tested the reproducibility of peak moment (PM) at velocities close to the maximum device capability, and in general, reproducibility results cannot be transferred to other devices or test protocols. The purpose of this study was to evaluate the reproducibility of PM for different isometric and isokinetic knee extension exercises using the IsoMed 2000. METHODS: Thirty subjects volunteered in three repeated test sessions, including isometric knee extension (100° and 140° knee angle) and isokinetic knee extension (30°/s and 400°/s). Statistical analysis for comparison of sessions two and three included paired sample t-test, calculation of intraclass correlation coefficient (ICC) and standard error of measurement (SEM). Additionally, Bland Altman statistics and corresponding plots were created. RESULTS: A significant difference between sessions in PM was found for isometric knee extension in one leg (140° left). Reproducibility was high for all conditions with ICC ranging from 0.964 to 0.988 and SEM in the range of 7.6 to 10.5 Nm. Bland Altman statistics revealed a bias between - 7.3 and 0.7 Nm. CONCLUSIONS: Reproducibility of PM using the IsoMed 2000 was good after an initial familiarization trial with high values of relative reproducibility. Absolute reproducibility can be interpreted as appropriate for most common practical applications.

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.

Oxygen Uptake Kinetics in Endurance Trained Youth and Adult Cyclists.

Previous studies reported faster pulmonary oxygen uptake kinetics at the onset of exercise in untrained youth compared with adults. Whether or not these differences are identical for trained groups have not been examined. The purpose of this study was to compare ˙VO2 kinetics of youth and adult cyclists at moderate and heavy-intensity exercise. Thirteen adult (age: 23.2 ± 4.8 years; ˙VO2peak 68.4 ± 6.8 mL·min-1.kg-1) and thirteen youth cyclists (age: 14.3 ± 1.5 years; ˙VO2peak 61.7 ± 4.3 mL·min-1.kg-1) completed a series of 6-min square wave exercises at moderate and heavy-intensity exercise at 90 rev·min-1. A two-way repeated-measure ANOVA was conducted to identify differences between groups and intensities. The time constant, time delay and the mean response time were not significantly different between youth and adult cyclists (p > 0.05). We found significant differences between intensities, with a faster time constant during moderate than heavy-intensity exercise in youth (24.1 ± 7.0 s vs. 31.8 ± 5.6 s; p = 0.004) and adults (22.7 ± 5.6 s vs. 28.6 ± 5.7 s; p < 0.001). The present data suggest that the effect of training history in adult cyclists compensate for the superior primary response of the oxygen uptake kinetics typically seen in youth compared to adults. Furthermore, the ˙VO2 response is dependent of work rate intensity in trained youth and adult cyclists.