Sex differences in the oxygen uptake kinetic response to heavy-intensity exercise in prepubertal children.

It has been demonstrated that there are no sex differences in the oxygen uptake (V(.)O(2)) kinetic response to moderate intensity exercise. However, sex differences in the response to maximal exercise are readily apparent even in the prepubertal years. The purpose of this study was therefore to investigate if sex differences exist in the V(.)O(2) kinetic response to heavy-intensity exercise. Forty-eight prepubertal children (25 male, 23 female) completed four transitions from baseline to 40% of the difference between their previously determined T(V-slope) (ventilatory threshold determined by the V-slope method) and peak V(.)O(2) on an electronically braked cycle ergometer. Each subject's breath-by-breath responses were interpolated to 1 s intervals, time aligned and averaged. The data following phase 1 were fit with: (1) a double exponential model and (2) a single exponential model within a fitting window that was previously identified to exclude the slow component. There were no significant differences in the parameters of the primary component between each model. Subsequent analysis was carried out using model 2. The primary time constant (tau(1)) was significantly (P<0.05) faster in boys [17.6 (5.8) s] than girls [21.9 (8.2) s], and the slow component contribution to the total change in amplitude after 9 min was significantly greater in girls [11.8 (5.5)%] than boys [8.9 (3.7)%]. Sex differences in the kinetic response to heavy-intensity exercise were identified and suggest that during the prepubertal years, sex differences exist in the ability to deliver and/or utilise oxygen in children.