The mechanism by which exercise improves mucocili-
ary clearance is related to both sympathetic and parasym-
pathetic stimulation. Increased ventilation stimulates up-
per-airway receptors. This results in increased vagal
activity, which in turn accelerates mucociliary clearance
due to the increase in mucus secretion. Moreover, physical
exercise leads to high levels of plasma catecholamines
(epinephrine and norepinephrine), which stimulate sympa-
thetic activity and consequently accelerate ciliary beat frequency.7,41,42