Influence of exercise intensity on pulmonary oxygen uptake kinetics at the onset of exercise and recovery in male adolescents.

The dynamics of the pulmonary oxygen uptake (VO2) responses to square-wave changes in work rate can provide insight into bioenergetic processes sustaining and limiting exercise performance. The dynamic responses at the onset of exercise and during recovery have been investigated systematically and are well characterized at all intensities in adults; however, they have not been investigated completely in adolescents. We investigated whether adolescents display a slow component in their VO2 on- and off-kinetic responses to heavy- and very heavy-intensity exercise, as demonstrated in adults. Healthy African American male adolescents (n=9, 14-17 years old) performed square-wave transitions on a cycle ergometer (from and to a baseline work rate of 20 W) to work rates of moderate (M), heavy (H), and very heavy (VH) intensity. In all subjects, the VO2 on-kinetics were best described with a single exponential at moderate intensity (tau1, on=36+/-11 s) and a double exponential at heavy (tau1, on=29+/-9 s; tau2, on=197+/-92 s) and very heavy (tau1, on=36+/-9 s; tau2, on=302+/-14 s) intensities. In contrast, the VO2 off-kinetics were best described with a single exponential at moderate (tau1, off=48+/-9 s) and heavy (tau1, off=53+/-7 s) intensities and a double exponential at very heavy (tau1, off=51+/-3 s; tau2, off=471+/-54 s) intensity. In summary, adolescents consistently displayed a slow component during heavy exercise (on- but not off-transition) and very heavy exercise (on- and off-transitions). Although the overall response dynamics in adolescents were similar to those previously observed in adults, their specific characterizations were different, particularly the lack of symmetry between the on- and off-responses.