Dependence of muscle o2 on blood flow dynamics at the onset of
forearm exercise.
Hughson, R. L., J. K. Shoemaker, M. E. Tschakovsky, and J. M.
Kowalchuk.
Department of Kinesiology, University of Waterloo, Waterloo,
Ontario N2L 3G1, Canada and Faculty of Kinesiology, and Department of
Physiology, University of Western Ontario, London, Ontario N6A 3K7,
Canada
APStracts 3:0252A, 1996.
The hypothesis that the rate of increase in muscle oxygen uptake (O2)
at the onset of exercise is influenced by muscle blood flow was
tested during forearm exercise with the arm either above or below
heart level to modify perfusion pressure. Ten young men exercised at
a power of approximately 2.2 W, and 5 of these subjects also worked
at 1.4 W. Blood flow to the forearm was calculated from the product
of blood velocity and cross-sectional area obtained with Doppler
techniques. Venous blood was sampled from a deep forearm vein to
determine O2 extraction. The rate of increase of muscle O2 and blood
flow was assessed from the mean response time (MRT) which is the time
to achieve approximately 63% increase from baseline to steady state.
In the arm below heart position during the 2.2 W exercise, blood flow
and muscle O2 both increased with an MRT of approximately 30 s. With
the arm above the heart at this power, the MRT for blood flow
(79.8+/-15.7 s, mean+/-SE) and muscle O2 (50.2+/-4.0 s) were both
significantly slower. Consistent with these findings were the greater
increases in venous plasma lactate concentration over resting values
in the above position (2.8+/-0.4 mmol/l) than in the below position
(0.9+/-0.2 mmol/l). At the lower power, both blood flow and muscle O2
also increased more rapidly with the arm below compared to above the
heart. These data support the hypothesis that changes in blood flow
at the onset of exercise have a direct effect on oxidative metabolism
through alterations in O2 transport.
Received 24 January 1996; accepted in final form 21 May 1996.
APS Manuscript Number A80-6.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 5 June 96