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; ̇VO_2peak 68.4 ± 6.8 mL·min^-1.kg^-1) and thirteen youth cyclists (age: 14.3 ± 1.5 years; ̇VO_2peak 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.

• No differences in the primary response between youth and adult cyclists at moderate and heavy-intensity exercise

• This suggests that adaptations to long-term training have a high potential as an influencing factor on the response of oxygen uptake kinetics

• Oxygen uptake kinetics are influenced by work rate in both youth and adult cyclists with a slower response at higher work rates.