Journal of Applied Physiology, Vol 67, Issue 1 324-329, Copyright © 1989 by American Physiological Society
Forearm metabolic asymmetry detected by 31P-NMR during submaximal exercise
J. R. Minotti, E. C. Johnson, T. L. Hudson, R. R. Sibbitt, L. E. Wise, E. Fukushima and M. V. Icenogle
Department of Internal Medicine, Veterans Administration Medical Center, Albuquerque, New Mexico.
This study evaluated the relationship of skeletal muscle energy metabolism
to forearm blood flow and muscle mass in the dominant (D) and nondominant
(ND) forearms of normal subjects. 31P-Magnetic resonance spectroscopy was
used to determine intracellular pH and the ratio of inorganic phosphate to
phosphocreatine (Pi/PCr), an index of energy metabolism. Forearm blood flow
and muscle mass were measured by venous occlusion plethysmography and
magnetic resonance imaging, respectively. Metabolic measurements and flow
were determined at rest and during submaximal exercise in both forearms.
After a warm-up period, six normal right-handed male subjects performed 7.5
min of wrist flexion exercise in the magnet (1 contraction every 5 s),
first with the ND forearm and then with the D forearm, at 23, 46, and 69
J/min. At rest, there were no differences between forearms in Pi/PCr or pH.
However, at each work load the D forearm demonstrated significantly lower
Pi/PCr and higher pH than the ND forearm. Blood flow was not significantly
different between the forearms at rest or during exercise. Because these
subjects were not engaged in unilateral arm training, we conclude that 1)
Pi/PCr is lower and pH is higher in the D compared with the ND forearm in
normal subjects during submaximal exercise, 2) these differences are
independent of muscle mass and blood flow, and 3) the cumulative effect of
long-term, low-level daily activity provides an adequate training stimulus
for muscular metabolic adaptations.
