AUTHOR=Chambault Julie , Grand Grégorine , Kayser Bengt 

TITLE=Sex-Specific Effects of Respiratory Muscle Endurance Training on Cycling Time Trial Performance in Normoxia and Hypoxia

JOURNAL=Frontiers in Physiology

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2021.700620

DOI=10.3389/fphys.2021.700620

ISSN=1664-042X

ABSTRACT=<p><bold>Objectives:</bold> We tested the hypotheses that respiratory muscle endurance training (RMET) improves endurance cycling performance differently in women and men and more so in hypoxia than in normoxia.</p><p><bold>Design:</bold> A prospective pre–post cross-over study with two testing conditions.</p><p><bold>Methods:</bold> Healthy and active women (seven, 24 ± 4 years, mean ± standard deviation [SD]) and men (seven, 27 ± 5 years) performed incremental cycling to determine maximum oxygen consumption (VO<sub>2peak</sub>) and power output (W<sub>peak</sub>) and on different days two 10-km cycling time trials (TTs) in normoxia and normobaric hypoxia (FiO<sub>2</sub>, 0.135, ~3,500 m equivalent), in a balanced randomized order. Next they performed supervised RMET in normoxia (4 weeks, 5 days/week, 30 min/day eucapnic hyperpnea at ~60% predicted maximum voluntary ventilation) followed by identical post-tests. During TTs, heart rate, ear oximetry reading, and W<sub>peak</sub> were recorded.</p><p><bold>Results:</bold> The VO<sub>2peak</sub> and W<sub>peak</sub> values were unchanged after RMET. The TT was improved by 7 ± 6% (<italic>p</italic> &lt; 0.001) in normoxia and 16 ± 6% (<italic>p</italic> &lt; 0.001) in hypoxia. The difference between normoxic and hypoxic TT was smaller after RMET as compared with that before RMET (14% <italic>vs</italic>. 21%, respectively, <italic>p</italic> &lt; 0.001). All effects were greater in women (<italic>p</italic> &lt; 0.001). The RMET did not change the heart rate or ear oximetry reading during TTs.</p><p><bold>Conclusion:</bold> We found a greater effect of RMET on cycling TT performance in women than in men, an effect more pronounced in hypoxia. These findings are congruent with the contention of a more pronounced performance-limiting role of the respiratory system during endurance exercise in hypoxia compared with normoxia and more so in women whose respiratory system is undersized compared with that of men.</p>