"Dyspnea" refers to the awareness of breathing discomfort that is typically experienced
during exercise in health and disease. In various participant populations, dyspnea is a
predictor of disability and death; and contributes to exercise intolerance and an adverse
health-related quality-of-life. It follows that alleviating dyspnea and improving exercise
tolerance are among the principal goals of disease management. Nevertheless, the effective
management of dyspnea and activity-limitation remains an elusive goal for many healthcare
providers and current strategies aimed at reversing the underlying chronic disease are only
partially successful in this regard. Thus, research aimed at identifying dyspnea-specific
medications to complement existing therapies for the management of exertional symptoms is
timely and clinically relevant. The purpose of this study is to test the hypothesis that
single-dose inhalation of fentanyl citrate (a mu-opioid receptor antagonist) will improve the
perception of dyspnea during strenuous exercise in healthy, young men in the presence of an
external thoracic restriction. To this end, the investigators plan compare the effects of
inhaled 0.9% saline placebo and inhaled fentanyl citrate (250 mcg) on detailed assessments of
neural respiratory drive (diaphragm EMG), ventilation, breathing pattern, dynamic operating
lung volumes, contractile respiratory muscle function, cardio-metabolic function and dyspnea
(sensory intensity and affective responses) during symptom-limited, high-intensity,
constant-work-rate cycle exercise testing with and without external thoracic restriction in
healthy, men aged 20-40 years.