However, this approach is rarely used in mice, and a brief overview of
the results obtained with this technique shows that mice do not display
a graded increase of heart rate during exercise, but rather a sharp shift of
cardiovascular indices to extremely high levels at the onset of locomotion
[7,8]. This “yes or no” response is still more surprising when data
for other systems responding to physical load are considered. For instance,
oxygen consumption, the other classic correlate of increased
metabolic demand during physical activity is responding to increase in
running speed gradually and the resulting curves in mice are similar
to those in any other species [9].