BACKGROUND: Marathon and ultramarathon running are sufficient to induce pulmonary dysfunction and respiratory muscle fatigue. However, it is unknown how the respiratory system responds to multiple, consecutive days of endurance exercise.
METHODS: Eleven well-trained endurance runners (8 male, 3 female) contested an ultra-endurance challenge comprising 10 marathons in 10 consecutive days. Lung function (FVC, FEV1, FEV1/FVC, PEF) and maximal static inspiratory and expiratory mouth pressures (MIP and MEP) were measured before and after marathon 1, 4, 7 and 10. Perceptual ratings of breathlessness (Borg CR10), respiratory muscle soreness (Visual Analogue Scale), and symptoms of upper-respiratory tract infection (URTI) were also recorded.
RESULTS: Group mean time for the 10 marathons was 276 ± 35 min, and post-marathon breathlessness was 2.0 ± 0.3 (range 1.0 to 3.0). Relative to pre-challenge baseline (159 ± 32 cmH2O), MEP was reduced after marathon 1 (136 ± 31 cmH2O, p = 0.017), marathon 7 (138 ± 42 cmH2O, p = 0.035) and marathon 10 (130 ± 41 cmH2O, p = 0.008), but there were no consistent reductions in baseline (pre-marathon) MEP. There were no changes in FVC, FEV1, FEV1/FVC, PEF, MIP, perception of breathlessness or respiratory muscle soreness throughout the challenge (p > 0.05). Moreover, there was no change in symptoms of URTI during and up to 2-weeks following the challenge (p > 0.05).
CONCLUSIONS: Ten days of marathon running did not induce a chronic reduction in resting pulmonary or respiratory muscle function, despite acute pre-to-post-marathon reductions in maximal expiratory muscle strength. These data underscore the robustness of the healthy respiratory system.