In 12-lead electrocardiography (ECG), detection of myocardial ischemia is b
ased on ST-segment changes in exercise testing. Magnetocardiography (MCG) i
s a complementary method to the ECG for a noninvasive study of the electric
activity of the heart. In the MCG, ST-segment changes due to stress have a
lso been found in healthy subjects. To further study the normal response to
exercise, we performed MCG mappings in 12 healthy volunteers during supine
bicycle ergometry. We also recorded body surface potential mappings (BSPM)
with 123 channels using the same protocol. In this paper we compare, for t
he first time, multichannel MCG recorded in bicycle exercise testing with B
SPM over the whole thorax in middle-aged healthy subjects. We quantified ch
anges induced by the exercise in the MCG and BSPM with parameters based on
signal amplitude, and correlation between signal distributions at rest and
after exercise. At the ST-segment and T-wave apex, the exercise induced a m
agnetic field component outward the precordium and the minimum value of the
MCG signal over the mapped area was found to be amplified. The response to
exercise was smaller in the BSPM than in the MCG. A negative component in
the MCG signal at the repolarization period of the cardiac cycle should be
considered as a normal response to exercise. Therefore, maximum ST-segment
depression over the mapped area in the MCG may not be an eligible parameter
when evaluating the presence of ischemia.