Resistance exercise-induced fluid shifts: change in active muscle
size and plasma volume.
Ploutz-Snyder, L. L., V. A. Convertino, and G. A. Dudley.
Department of Biological Sciences, Ohio University, Athens, Ohio
45701 and Biomedical Operations and Research Office, National
Aeronautics and Space Administration, Kennedy Space Center, Florida
32899
APStracts 2:0100R, 1995.
The purpose of this study was to test the hypothesis that the
reduction in plasma volume (PV) induced by resistance exercise
reflects fluid loss to the extravascular space and subsequently
selective increase in cross-sectional area (CSA) of active but not
inactive skeletal muscle. We compared changes in active and inactive
muscle CSA and PV after barbell squat exercise. Magnetic resonance
imaging (MRI) was used to quantify muscle involvement in exercise and
to determine CSA of muscle groups or individual muscles (vasti VS,
adductor ADD, hamstring HAM, and rectus femoris RF). Muscle
involvement in exercise was determined using exercise-induced
contrast shift in T2 weighted MR images immediately post-exercise.
Alterations in muscle size were based on the mean CSA of individual
slices. Hematocrit, hemoglobin, and Evans blue dye were used to
estimate changes in PV. Muscle CSA and PV data were obtained pre- and
immediately post-exercise, and 15, and 45 min thereafter. A hierarchy
of muscle involvement in exercise was found such that VS > ADD >
HAM > RF, with the HAM and RF showing essentially no involvement.
CSA of the VS and ADD muscle groups were increased 10% and 5%,
respectively, immediately after exercise in each thigh with no
changes in HAM and RF CSA. PV was decreased 22% immediately following
exercise. The absolute loss of PV was correlated (R2=0.75) with
absolute increase in muscle CSA immediately post-exercise supporting
the notion that increased muscle size after resistance exercise
reflects primarily fluid movement from the vascular space into active
but not inactive muscle.
Received 6 May 1994; accepted in final form 23 March 1995.
APS Manuscript Number R239-4.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 25 April 1995.