Continuous exercise induces airway epithelium damage while a matched-intensity and volume intermittent exercise does not

Background: While continuous exercise (CE) induces greater ventilation (V _E) when compared to intermittent exercise (IE), little is known of the consequences on airway damage. Our aim was to investigate markers of epithelial cell damage - i.e. serum levels of CC16 and of the CC16/SP-D ratio - during and following a bout of CE and IE of matched work. Methods: Sixteen healthy young adults performed a 30-min continuous (CE) and a 60-min intermittent exercise (IE; 1-min work: 1-min rest) on separate occasions in a random order. Intensity was set at 70% of their maximum work rate (WR _max). Heart rate (HR) and V V _E were measured throughout both tests. Blood samples were taken at rest, after the 10th min of the warm-up, at the end of both exercises, half way through IE (matched time but 50% work done for IE) as well as 30- and 60-min post-exercise. Lactate and CC16 and SP-D were determined. Results: Mean V V _E was higher for CE compared to IE (85 ± 17 l.min ^{- 1} vs 50 ± 8 l.min ^{- 1}, respectively; P < 0.001). Serum-based markers of epithelial cell damage remained unchanged during IE. Interaction of test × time was observed for SP-D (P = 0.02), CC16 (μg.l ^{- 1}) (P = 0.006) and CC16/SP-D ratio (P = 0.03). Maximum delta CC16/SP-D was significantly correlated with mean V V _E sustained (r = 0.83, P < 0.001) during CE but not during IE. Conclusion: The 30-min CE performed at 70% WR _max induced mild airway damage, while a time- or work-matched IE did not. The extent of the damage during CE was associated with the higher ventilation rate.