The purpose of this study was to determine if inspiratory muscle training (IMT) alters the oxygen cost of breathing (VO(2RM)) during voluntary hyperpnea. Sixteen male cyclists completed 6 wks of inspiratory muscle training (IMT) using an inspiratory load of 50% (IMT) or 15% [placebo] (CON) of maximal inspiratory pressure (PImax). Prior to training, a maximal incremental cycle ergometer test was performed to determine VO(2) and ventilation (V(E)) at multiple workloads. Pre- and post- training, subjects performed three separate 4-min bouts of voluntary eucapnic hyperpnea (mimic), matching V(E) that occurred at 50%, 75% and 100% of VO(2max). PI(max) was significantly increased (p0.05) were shown in the CON group. IMT significantly reduced the O(2) cost of voluntary hyperpnea, which suggests that a reduction in the O(2) requirement of the respiratory muscles following a period of IMT may facilitate increased O(2) availability to the active muscles during exercise. These data may provide an insight into the mechanism(s) underpinning the reported improvements in endurance performance following IMT, however, this awaits further investigation.