HighlightsWhat are the main findings?Exercise-induced bronchoconstriction (EIB) is a common problem in elite athletes. This study aimed to investigate the effects of systemic hydration on pulmonary function and to establish whether it can reverse dehydration-induced alterations in pulmonary function.Systemic hydration had a positive effect on both pulmonary function and exercise capacity (VO2max).What are the implications of the main findings?Hydration potentially plays a regulatory role in stabilizing the airway in elite athletes, protecting them from airway hyper-responsiveness.Of particular interest are the small airways, which appear to be affected independently or in combination with a decrease in FEV1 and proper hydration can protect them from further injury.AbstractBackground: Exercise-induced bronchoconstriction (EIB) is a common problem in elite athletes. Classical pathways in the development of EIB include the osmotic and thermal theory as well as the presence of epithelial injury in the airway, with local water loss being the main trigger of EIB. This study aimed to investigate the effects of systemic hydration on pulmonary function and to establish whether it can reverse dehydration-induced alterations in pulmonary function. Materials and Methods: This follow-up study was performed among professional cyclists, without a history of asthma and/or atopy. Anthropometric characteristics were recorded for all participants, and the training age was determined. In addition, pulmonary function tests and specific markers such as fractional exhaled nitric oxide (FeNO) and immunoglobulin E (IgE) were measured. All the athletes underwent body composition analysis and cardiopulmonary exercise testing (CPET). After CPET, spirometry was followed at the 3rd, 5th, 10th, 15th, and 30th min. This study was divided into two phases: before and after hydration. Cyclists, who experienced a decrease in Forced Expiratory Volume in one second (FEV1) ≥ 10% and/or Maximal Mild-Expiratory Flow Rate (MEF25–75) ≥ 20% after CPET in relation to the results of the spirometry before CPET, repeated the test in 15-20 days, following instructions for hydration. Results: One hundred male cyclists (n= 100) participated in Phase A. After exercise, there was a decrease in all spirometric parameters (p< 0.001). In Phase B, after hydration, in all comparisons, the changes in spirometric values were significantly lower than those in Phase A (p< 0.001). Conclusions: The findings of this study suggest that professional cyclists have non-beneficial effects on respiratory function. Additionally, we found that systemic hydration has a positive effect on spirometry in cyclists. Of particular interest are small airways, which appear to be affected independently or in combination with the decrease in FEV1. Our data suggest that pulmonary function improves systemic after hydration.