The measurement of carbon monoxide levels is a non-
invasive method considered to be the accepted standard
for detecting very recent smoking.15,46,47 The increased
levels in smokers confirmed this, as carbon monoxide lev-
els were more pronounced after acute smoking than after
smoking following aerobic exercise. This may be explained
by the effect of exercise, which increases breathing frequency and consequently increases elimination of carbon
monoxide.48 It is therefore assumed that exercise provided
the initial elimination of this gas to levels below those
found at rest.