Weavil, J. C., Stickford, J. A., Duke, J. W., Chapman, R. F., Stager, J. M., & Mickelborough, T. D. (2013). Impact of expiratory flow limitation on performance at simulated altitude. Medicine & Science in Sports & Exercise, 45(5), Supplement abstract number 1748.

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"Many athletes exhibit expiratory flow limitation during heavy exercise and consequently may be additionally challenged when exercising at moderate altitude."

This study determined how expiratory flow limitation affects aerobic performance at modest altitude. It was hypothesized that non-flow limited athletes would be at a competitive advantage where altitude-induced declines in SaO2 present less of a consequence than the coincident increases in ventilation and work of breathing experienced by the non-flow limited athlete.

Flow limited (N = 7) and non-flow limited (N = 7) male cyclists performed three 5-km time-trials on a Velotron cycle ergometer on separate days. Expired gases were measured at rest and throughout each time-trial. Ss performed a familiarization trial followed by a single-blinded normoxic (FiO2 = 0.21) and hypoxic (FiO2 = 0.17, approximately 2,000 m altitude) trial in random order. Time-to-completion and average power output were used to assess performance.

Metabolic, ventilatory, and performance measures were similar between groups in normoxia. However, when the normoxic and hypoxic trials were compared, the expiratory flow limitation group had a significantly smaller time-to-completion and average power output than the non-flow limited group. During hypoxia, the flow-limited Ss had a significantly higher VE/VO2, VE/ VCO2, and SaO2 than the non-flow limited group at the 5th km. The main effects of hypoxia on VO2, VCO2, and SaO2 were significantly decreased as compared to normoxia in both groups.

Implication. Expiratory flow-limited athletes are more able to effectively maintain normoxic 5km time-trial performance at a simulated moderate altitude than non-flow limited athletes. Non-flow limited athletes did not defend SaO2 in hypoxia by encroaching upon their ventilatory reserve capacity and increasing alveolar ventilation. The reduced SaO2 in hypoxia for the non-flow limited group, compared to the flow-limited group, may impair oxygen delivery to the limb locomotor muscles resulting in a greater reduction in cycling performance. Flow limitation status may be an important consideration for cyclists when selecting races, especially since the data from the present study suggests that flow-limited athletes may have an advantage against non-flow limited athletes at moderate altitude.

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