Expiratory flow limitation under moderate hypobaric hypoxia does not influence ventilatory responses during incremental running in endurance runners

We tested whether expiratory flow limitation ( EFL ) occurs in endurance athletes in a moderately hypobaric hypoxic environment equivalent to 2500 m above sea level and, if so, whether EFL inhibits peak ventilation ( V ˙ E peak ), thereby exacerbating the hypoxia‐induced reduction in peak oxygen uptake ( V ˙ O 2peak ). Seventeen young male endurance runners performed incremental exhaustive running on separate days under hypobaric hypoxic (560 mmHg) and normobaric normoxic (760 mmHg) conditions. Oxygen uptake ( V ˙ O 2 ), minute ventilation ( V ˙ E), arterial O 2 saturation (SpO 2 ), and operating lung volume were measured throughout the incremental exercise. Among the runners tested, 35% exhibited EFL ( EFL group, n  = 6) in the hypobaric hypoxic condition, whereas the rest did not (Non‐ EFL group, n  = 11). There were no differences between the EFL and Non‐ EFL groups for V ˙ E peak and V ˙ O 2peak under either condition. Percent changes in V ˙ E peak (4 ± 4 vs. 2 ± 4%) and V ˙ O 2peak (−18 ± 6 vs. −16 ± 6%) from normobaric normoxia to hypobaric hypoxia also did not differ between the EFL and Non‐ EFL groups (all P  > 0.05). No differences in maximal running velocity, SpO 2 , or operating lung volume were detected between the two groups under either condition. These results suggest that under the moderate hypobaric hypoxia (2500 m above sea level) frequently used for high‐attitude training, ~35% of endurance athletes may exhibit EFL , but their ventilatory and metabolic responses during maximal exercise are similar to those who do not exhibit EFL .