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Department of Exercise Science, University of Iowa, Iowa City, Iowa 52242
We imposed opposing oscillations in
treadmill speed and grade on nine rats to test for direct mechanical
coupling between stride frequency and hindlimb blood flow. Resting
hindlimb blood flow was 15.5 ± 1.7 ml/min. For 90 s at 7.5 m/min, rats alternated walking at 
10° for 10 s and +10° for
10 s. This elicited oscillations in hindlimb blood flow having an
amplitude of 4.1 ± 0.5 ml/min (18% of mean flow) with a delay
presumably due to metabolic vasodilation. Similar oscillations in speed
(5.5-9.5 m/min) elicited oscillations in hindlimb blood flow
(amplitude 3.4 ± 0.5 ml/min, 15% of mean flow) with less of a
delay, possibly due to changes in vasodilation and muscle pump
function. We then simultaneously imposed these speed and grade
oscillations out of phase (slow uphill, fast downhill). The rationale
was that the oscillations in vasodilation evoked by the opposing
oscillations in speed and grade would cancel each other, thereby
testing the degree to which stride frequency affects hindlimb blood
flow directly (i.e., muscle pumping). Opposing oscillations in speed
and grade evoked oscillations in hindlimb blood flow having an
amplitude of 3.3 ± 0.6 ml/min (16% of mean flow) with no delay
and directly in phase with the changes in speed and stride
frequency. The finding that hindlimb blood flow changes
directly with speed (when vasodilation caused by changes in speed and
grade oppose each other) indicates that there is a direct
coupling of stride frequency and hindlimb blood flow (i.e.,
muscle pumping).
exercise hyperemia; metabolic vasodilation; rat
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