THE ROLE OF EXPIRATORY FLOW LIMITATION IN THE OXYGEN COST OF EXERCISE HYPERPNEA IN HIGHLY-TRAINED DISTANCE RUNNERS

Abstract

There is an upper limitation to the flow rates achievable during exhalation. Once this limitation is reached (expiratory flow limitation; FLexp), such as that observed during intensive exercise, no further increase in expiratory flow is possible. During heavy to maximal exercise, a major consequence of FLexp may be an increased oxygen cost of breathing. To examine the effect of FLexp on respiratory muscle oxygen consumption (VO2RM) during maximal exercise, a sample of highly-trained male distance runners (n=18; O2 max = 74.28 ml·kg-1·min-1) completed an incremental exercise test to exhaustion on a treadmill. Based on flow-volume loop analysis, subjects were separated into two groups, flow-limited (FL) and non-flow limited (NFL). During a second visit, runners performed three separate trials of voluntary hyperpnea, matching exercise ventilation ( E) at 80%, 90%, and 100% of maximal exercise while standing on the treadmill. Respiratory muscle O2 consumption (VO2RM) was estimated during each voluntary hyperpnea trial. A one-tailed, independent samples t-test detected a significantly greater VO2RM in FL compared to NFL (P = 0.043). E at O2 max was also greater in FL vs. NFL (P = 0.029). No differences were found between expiratory reserve volume (ERV), tidal volume (VT), or breathing frequency (fb) during maximal exercise. When co-varying for E at O2 max, there was no significant difference in VO2RM between groups, suggesting that the greater oxygen cost of breathing in flow-limited individuals is a consequence of the greater VE and not due to differences in breathing mechanics associated with flow limitation.