Oxygen uptake kinetics and maximal aerobic power are unaffected by inspiratory muscle training in healthy subjects where time to exhaustion is extended

The aim of this study was to determine whether 4 weeks of inspiratory muscle training (IMT) would be accompanied by alteration in cardiopulmonary fitness as assessed through moderate intensity oxygen uptake (V̇O₂) kinetics and maximal aerobic power (V̇O_2max). Eighteen healthy males agreed to participate in the study [training group (Tra) n=10, control group (Con) n=8]. Measurements of spirometry and maximal static inspiratory mouth pressure (PI_max) were taken pre- and post-training in addition to: (1) an incremental test to volitional exhaustion, (2) three square-wave transitions from walking to running at a moderate intensity (80% ventilatory threshold) and (3) a maximal aerobic constant-load running test to volitional fatigue for the determination of time to exhaustion (T_lim). Training was performed using an inspiratory muscle trainer (Powerbreathe). There were no significant differences in spirometry either between the two groups or when comparing the post- to pre-training results within each group. Mean PI_max increased significantly in Tra (P<0.01) and showed a trend for improvement (P<0.08) in Con. Post-training T_lim was significantly extended in both Tra [232.4 (22.8) s and 242.8 (20.1) s] (P<0.01) and Con [224.5 (19.6) and 233.5 (12.7) s] (P<0.05). Post-training T_lim was significantly extended in Tra compared to Con (P<0.05). In conclusion, the most plausible explanation for the stability in V̇O₂ kinetics and V̇O_2max following IMT is that it is due to insufficient whole-body stress to elicit either central or peripheral cardiopulmonary adaptation. The extension of post-training T_lim suggests that IMT might be useful as a stratagem for producing greater volumes of endurance work at high ventilatory loads, which in turn could improve cardiopulmonary fitness.