High muscle blood flows are not attenuated by recruitment of
additional muscle mass.
Richardson, Russell S., Brian Kennedy, Douglas R. Knight, and Peter D.
Wagner.
Department of Medicine, University of California, La Jolla, Ca
92093-0623
APStracts 2:0236H, 1995.
Recent studies have demonstrated that single leg knee-extensor
exercise elicits high mass specific blood flow () which, if
incremented towards maximum, in the presence of additional muscle
recruitment would soon outstrip the heart's pumping capacity and
blood pressure would fall. Thus, incremental single leg knee-extensor
exercise (KE) provides the opportunity to determine the intensity at
which, if at all, quadriceps muscle hemodynamics are altered during
incremental exercise which involves a substantially greater muscle
mass. Leg was measured during incremental KE and again with
superimposed incremental two legged knee-extensor exercise with
incremental arm cranking (A+L) in trained subjects (n=5). Leg and
vascular conductance (VC) increased with work rate (WR) to reach high
levels ( = 385.7 +/- 26 (KE) and 342.3 +/- 15 ml x min-1 x 100g-1
(A+L, p<0.05); VC at 90% of WRmax = 79 +/- 5 (KE) and 75 +/- 6
ml x min-1 x mmHg-1 (A+L)), but the /WR relationship and VC/WR
relationship in KE and A+L exercise were not different. O2max and the
O2/WR relationship of the quadriceps were also unaffected by the
additional muscle mass recruited. Despite a significantly greater net
femoral venous norepinephrine (NE) outflow at both 90 and 100% of
WRmax in A+L exercise (WRmax : 4216 +/- 1601 (A+L) and 901 +/- 99 ng
x ml-1 (KE), p<0.05) leg continued to rise linearly with WR.
These data indicate that despite almost a 3 and 5 fold increase in NE
spillover from the quadriceps muscle during A+L exercise compared to
KE exercise at 90 and 100% of WRmax, the high quadriceps can remain
uncompromised.
Received 6 March 1995; accepted in final form 30 May 1995.
APS Manuscript Number H209-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 July 1995.