Inspiratory muscle training enhances pulmonary O2 uptake kinetics and high-intensity exercise tolerance in humans

Bailey SJ, Romer LM, Kelly J, Wilkerson DP, DiMenna FJ, Jones AM. Inspiratory muscle training enhances pulmonary O-2 uptake kinetics and high-intensity exercise tolerance in humans. J Appl Physiol 109: 457-468, 2010. First published May 27, 2010; doi: 10.1152/japplphysiol.00077.2010.-Fatigue of the respiratory muscles during intense exercise might compromise leg blood flow, thereby constraining oxygen uptake ((V) over dotO(2)) and limiting exercise tolerance. We tested the hypothesis that inspiratory muscle training (IMT) would reduce inspiratory muscle fatigue, speed (V) over dotO(2) kinetics and enhance exercise tolerance. Sixteen recreationally active subjects (mean +/- SD, age 22 +/- 4 yr) were randomly assigned to receive 4 wk of either pressure threshold IMT [30 breaths twice daily at similar to 50% of maximum inspiratory pressure (MIP)] or sham treatment (60 breaths once daily at similar to 15% of MIP). The subjects completed moderate-, severe-and maximal-intensity "step" exercise transitions on a cycle ergometer before (Pre) and after (Post) the 4-wk intervention period for determination of (V) over dotO(2) kinetics and exercise tolerance. There were no significant changes in the physiological variables of interest after Sham. After IMT, baseline MIP was significantly increased (Pre vs. Post: 155 +/- 22 vs. 181 +/- 21 cmH(2)O; P < 0.001), and the degree of inspiratory muscle fatigue was reduced after severe- and maximal-intensity exercise. During severe exercise, the (V) over dotO(2) slow component was reduced (Pre vs. Post: 0.60 +/- 0.20 vs. 0.53 +/- 0.24 l/min; P < 0.05) and exercise tolerance was enhanced (Pre vs. Post: 765 +/- 249 vs. 1,061 +/- 304 s; P < 0.01). Similarly, during maximal exercise, the (V) over dotO(2) slow component was reduced (Pre vs. Post: 0.28 +/- 0.14 vs. 0.18 +/- 0.07 l/min; P < 0.05) and exercise tolerance was enhanced (Pre vs. Post: 177 +/- 24 vs. 208 +/- 37 s; P < 0.01). Four weeks of IMT, which reduced inspiratory muscle fatigue, resulted in a reduced (V) over dot O-2 slow-component amplitude and an improved exercise tolerance during severe- and maximal-intensity exercise. The results indicate that the enhanced exercise tolerance observed after IMT might be related, at least in part, to improved (V) over dotO(2) dynamics, presumably as a consequence of increased blood flow to the exercising limbs.