PURPOSE: To determine if inspiratory muscle training can affect the oxygen cost of breathing (VO2RM) during exercise.
METHODS: Using a double blind, placebo controlled design, 16 male cyclists completed 6 wks of inspiratory muscle training (IMT) using an inspiratory load of 50% (IMT; n=8) or 15% [placebo] (C; n=8)of maximal inspiratory pressure (PImax). Prior to training, a maximal incremental cycle ergometer test was performed to determine VO2 and ventilation (VE) at multiple workloads. Pre- and post- training, subjects performed three separate 4-min bouts of voluntary hyperpnea (mimic), matching VE that occurred at 50%, 75% and 100% of VO2max. During the mimic trials, target VE was maintained by the subjects using visual feedback, matching the measured exercise tidal volume (VT) and breathing frequency (FB). The O2 cost of hyperpnea was calculated by subtracting the VO2 measured at rest from those obtained during the final minute of the mimic trial. Statistical significance was established at p<0.05.
RESULTS: PImax significantly increased pre- to post- IMT by 22.5 ±3.1% (116±5 to 142±7cmH2O) in the IMT group and remained unchanged in the C group. Pre- IMT values for the O2 cost of ventilation at a VE of 55.39 ± 2.12L (50% VO2max) were 1.92 ± 0.37 mLO2/L/min and increased to 3.65 ± 0.29 mLO2/L/min at a VE of 157.04±7.86L (100% VO2max) in the IMT group. The VO2 RM required during the mimic trial corresponded to 4.4±0.5%, 6.5±0.5% and 12.9±1.4% of the total VO2 (VO2T) at ventilatory workloads equivalent to 50%, 75% and 100% of VO2max, respectively. Following IMT, the VO2 RM requirement significantly decreased by 1.1% (3.4±0.5% of VO2T) at 50% VO2max, 1.9% (4.3±0.8% of VO2T) at 75%VO2max, and 4.5% (8.4±1.5% of VO2T) at 100%VO2max. Heart rate during hyperpnea at 100%VO2max significantly decreased from 93±2 bpm to 85±1bpm from pre- to post- IMT. No significant changes were shown in the C group.
CONCLUSION: IMT significantly reduces the O2 cost of exercise hyperpnea. Thus, a reduction in the O2 requirement of the respiratory muscles during exercise may facilitate increased O2 availability to the limb locomotor muscles. These data may provide insight into the mechanism(s) involved in improved endurance performance following IMT.