Effects of Hypoxia on Locomotor-Respiratory Coupling During Exercise

Abstract

To determine if acute exposure to normobaric hypoxia alters locomotor-respiratory coupling (LRC) patterns typically observed in trained runners, 13 trained male distance runners performed a running economy (RE) and maximal oxygen uptake (V̇O2max) test in normoxia (NORM) and hypoxia (HYP) (FIO2 = 15.8%; ~ 2500m / 8000ft) on separate days. RE and LRC measures were taken during the fourth minute of each submaximal speed (12.9, 14.3, and 16.1 km hr-1), while ratings of perceived exertion (RPE) and dyspnea (DYS) were taken during the first 10 seconds of the final minute at each speed, and again at the conclusion of the maximal test. Stride frequency-to-breathing frequency quotients were significantly lower at each submaximal speed in HYP (12.9 km hr-1: 2.91 ± 0.20 vs. 2.45 ± 0.17, 14.3 km hr-1: 2.53 ± 0.17 vs. 2.21 ± 0.14, 16.1 km hr-1: 2.22 ± 0.14 vs. 1.95 ± 0.09; p < 0.05) due to increases in breathing frequency while maintaining stride frequency. Compared with NORM, the degree of LRC (range: 36 - 99%) was not significantly different at any of the three common submaximal speeds with exposure to HYP. However, the degree of LRC was increased at V̇O2max (43.8 ± 3.4% vs. 57.1 ± 3.8%; p < 0.05). Breathing frequency (breaths min-1) was significantly increased at each submaximal speed in HYP compared to NORM (12.9 km hr-1: 30.3 ± 1.9 vs. 35.9 ± 2.2; 14.3 km hr-1: 34.8 ± 2.0 vs. 39.8 ± 2.2; 16.1 km hr-1: 40.4 ± 2.4 vs. 45.2 ± 1.9; all speeds p < 0.05), but was not significantly different at V̇O2max. RE and RPE were not significantly different at any speed. DYS was only significantly different between NORM and HYP at 16.1 km hr-1 (p < 0.05). In conclusion, trained distance runners are able to maintain LRC in hypoxia, even when breathing frequency is increased at any submaximal pace. Within this unique population, years of training may enhance and optimize the ability to make adjustments to maintain LRC in order to minimize metabolic costs. However, there may be individual differences to LRC that could affect performance or the response to training at altitude.