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

Adrien Combes,Frédéric Daussin,Jeanne Dekerle,Rosie Twomey,Xavier Dumont,Valérie Bougault,Alfred Bernard

doi:10.1186/s12931-019-0978-1

Abstract

BackgroundWhile continuous exercise (CE) induces greater ventilation ( dot{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.MethodsSixteen 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 (WRmax). Heart rate (HR) and dot{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.ResultsMean dot{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 dot{V} E sustained (r = 0.83, P < 0.001) during CE but not during IE.ConclusionThe 30-min CE performed at 70% WRmax 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.

Highlights

While continuous exercise (CE) induces greater ventilation (V_ E) when compared to intermittent exercise (IE), little is known of the consequences on airway damage
forced expiratory volume in one second (FEV1): Forced expiratory volume in one second; FVC: forced vital capacity; VO2 max: maximal oxygen uptake; WRmax: incremental maximum work rate, VEmax: maximal voluntary ventilation, MVVt: theoretical maximal voluntary ventilation = 35 × FEV1; Bf: breathing frequency; VT: tidal volume; HR: Heart rate; HRtmax: theoretical maximal heart rate (220-age) for IE, where mean V_E was 34 ± 4% of V_Emax, 31 ± 6% of MVVt and 79 ± 10% of V_E at Gas exchange threshold (GET)
The present study demonstrates that 30 min of CE performed at an intensity of 70% of WRmax, corresponding approximately to the intensity of the GET, induces more airway damage than the same work done in 60 min of IE (1 min work / 1 min rest) in healthy young participants

Summary

Introduction

While continuous exercise (CE) induces greater ventilation (V_ E) when compared to intermittent exercise (IE), little is known of the consequences on airway damage. Due to the lower levels of ventilation, MIIT is more likely to preserve the integrity of the airways in populations suffering from respiratory disease that are characterized by chronic airway inflammation and remodeling. High intensity exercise sustained for several minutes may induce significant airway inflammation and/or trigger exercise-induced bronchoconstriction or asthma [1, 10, 11]. The higher ventilation rate with continuous exercise (CE) for the same intensity of exercise may bring along greater stress onto the epithelium cells of the airways. If there is evidence of less damage to the epithelium with IE, this may be a reason to recommend IE over CE in some practical settings

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