Current Knowledge/Study Rationale: Although life expectancy can be predicted by absolute values of maximal oxygen uptake, the underlying factors and their interactions remain elusive. We therefore hypothesized that obesity, irregular exercise, superficial sleep, sleep-disordered breathing, and impaired lung function were mutually interactive with each other, in addition to each factor being associated individually with low exercise capacity.
Study Impact: In our study of male workers, structural equation modeling is a promising method for unraveling the complex potential factors linked to low cardiorespiratory fitness. Our results suggest that objectively measured disrupted sleep is associated not only with several medical problems, as identified by previous studies, but also with low cardiorespiratory fitness. In addition, individuals with limited exercise capacity without definite causes should undertake a sleep study, particularly in those describing symptoms of sleep-disordered breathing or insomnia.