The aim of this work was to investigate the effects of a twelve-week moderate intensity aerobic exercise program on respiratory health of previously sedentary adults. Moreover, the hypothesis that sigh breath variability in terms of both rate and amplitude could be an indicator of lung health was tested for the first time. The work will be presented in six chapters, the content of which is briefly summarized below. The first chapter of this thesis provides a general description of the respiratory system. The second chapter provides a review of the measurements performed to assess the health status of the respiratory system.