Locomotor-Respiratory Coupling is Maintained in Hypoxia in Trained Distance Runners

Abstract

PURPOSE: To determine if acute exposure to normobaric hypoxia alters locomotor-respiratory coupling (LRC) patterns typically observed in trained runners, and to determine if any changes in LRC influence running economy (RE) and/or perceptions of ventilatory effort. METHODS: Trained male distance runners (n=13) with VO2max = 66.8 ± 1.1 ml kg-1 min-1 completed two laboratory visits, each in a different inspired gas condition, either normoxia (NORM) or hypoxia (HYP) (FIO2 = 15.8%; ~ 2500 m/8000ft). During each visit, subjects ran for 5 min at each of three constant submaximal speeds of 12.9, 14.3, and 16.1 km hr-1 with 4 min standing rest between speeds. Following the third stage, an incremental incline ramp protocol was used to determine VO2max. RE and LRC measures were taken during the 4th min of each speed (3:00–4:00), while ratings of perceived exertion (RPE) and dyspnea (DYS) were taken during the first 30 seconds of the final minute at each speed (4:00–4:30), and again at the conclusion of the test. The degree of LRC was calculated as the highest number of inspirations or expirations beginning in the same decile of the step divided by the total number of breaths. RESULTS: Compared with NORM, the degree of LRC was not significantly different at any of the three common submaximal speeds with exposure to HYP, however it was increased at VO2max (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 (30.3 ± 1.9 vs. 35.9 ± 2.2, 34.8 ± 2.0 vs. 39.8 ± 2.2, 40.4 ± 2.4 45.2 ± 1.9; p < 0.05), but was not significantly different at VO2max. Stride frequency-to-breathing frequency quotients were significantly lower at each submaximal speed in HYP (2.91 ± 0.20 vs. 2.45 ± 0.17, 2.53 ± 0.17 vs. 2.21 ± 0.14, 2.22 ± 0.14 vs. 1.95 ± 0.09; p < 0.05) due to increases in breathing frequency while maintaining stride frequency. 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). CONCLUSIONS: Trained distance runners are able to maintain LRC in hypoxia, even when breathing frequency is increased at any submaximal pace. It is possible that within this unique population, years of training enhance and optimize the ability to make adjustments to LRC in order to minimize metabolic costs.