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Department of Exercise Science, University of Iowa, Iowa City, Iowa 52242
Previous
studies examining the delay to the onset of vasodilation have primarily
focused on the onset of exercise, a setting complicated by the fact
that the muscle pump and the vasodilator systems are both activated,
making it difficult to attribute changes in blood flow to one or
both. The goal here was to determine the delay to the onset of
vasodilation after changes in work rate imposed by changes in treadmill
grade (work intensity) during locomotion at a steady speed. The
rationale was that constant speed would help ensure constant muscle
pump activity (contraction frequency) such that vasodilator responses
could be examined in isolation. Seven Sprague-Dawley rats underwent
three trials each in which treadmill incline was suddenly (~1 s)
elevated from
10° to +10°. The delay to the onset of vasodilation
averaged 5.0 ± 1.8 s, and this delay was not altered by
inhibition of nitric oxide synthase. Similar or longer delays were seen
during sinusoidal exercise. Thus there is a significant delay before
the onset of vasodilation after an increase in work intensity (muscle
force) during locomotory exercise at constant speed.
muscle blood flow; arterial pressure; vascular conductance; exercise
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