Will Burton1, Sarah Ridgeway1, Katherine Cox1, Joshua Smith2, Nicholas Luden1, Michael Saunders, FACSM1, Stephanie Kurti1. 1Human Performance Laboratory, James Madison University, Harrisonburg, VA. 2Department of Cardiovascular Medicine, Mayo Clinic, Rochester, MN.

BACKGROUND: Expiratory flow limitation (EFL) poses a potential mechanical limitation of the pulmonary system during maximal exercise in endurance-trained athletes, but the prevalence in females and males of pubertal age is not well understood. The purpose of this investigation was to assess EFL presence in endurance-trained (ET) youth males and females compared to a recreationally active (RA) control group. METHODS: Youth ET male (n=12, 16.3 ± 1.0 y), RA male (n=12, 17.6 ± 2.2 y), ET female (n=9, 15.8 ± 1.1 y), and RA female (n=10, 16.8 ± 1.6 y) subjects completed an incremental exercise test to exhaustion on a cycle ergometer to determine peak oxygen consumption (VO2peak). Maximal flow volume loops (MFVL) were performed pre- and post-exercise to assess forced vital capacity (FVC), forced expiratory volume in 1 second (FEV1), FEV1/FVC, forced expiratory flow between 25% and 75% of FVC (FEF25-75% of FVC) and peak expiratory flow (PEF). Inspiratory capacity (IC) maneuvers were performed the last 20 seconds of every stage. EFL was quantified as the percentage of the expiratory tidal volume that overlapped with the MFVL. RESULTS: EFL prevalence was higher in ET males and females at VO2peak (18/21 subjects; 11/12 males, 7/9 females) compared to RA male and female subjects (7/22 subjects; 5/12 males, 2/10 females) (p < 0.05). ET females had significantly greater EFL severity than RA females at maximal exercise (57.0 ± 36.4%, 13.3 ± 32.2%, respectively, p = 0.013), while there was no difference in EFL severity between ET and RA males (p = 0.473). ET males also had significantly greater EFL severity at maximal exercise compared to RA males (75.0 ± 32.9%, 29.7 ± 40.4%, p = 0.007). There was no difference in the prevalence and severity of flow-limitation between ET males and females or between RA males and females (p’s > 0.05). CONCLUSIONS: Both ET male and ET female cyclists demonstrated greater prevalence and severity of EFL at maximal exercise than respective same-sex RA subjects of similar age, height, and lung size. Further research should be conducted to determine whether EFL may limit exercise performance in this population and whether EFL exists into adulthood.

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