Mixed muscle protein synthesis and breakdown following resistance
exercise in humans.
Phillips, Stuart M., Kevin D. Tipton, Asle Aarsland, Steven E. Wolf,
and Robert R. Wolfe.
Metabolism Unit, Shriners Burns Institute, Departments of Surgery,
Anesthesiology, University of Texas Medical Branch, Galveston, TX,
77550
APStracts 4:0059E, 1997.
Mixed muscle protein fractional synthesis rate (FSR) and fractional
breakdown rate (FBR) were examined following an isolated bout of
either concentric or eccentric resistance exercise. Subjects were 8
untrained volunteers (4 males, 4 females). Mixed muscle protein FSR
and FBR were determined using primed constant infusions of d5
-phenylalanine and 15N-phenylalanine, respectively. Subjects were
studied in the fasted state on 4 occasions: at rest, and 3h, 24h, and
48h following a resistance exercise bout. Exercise was 8 sets of 8
concentric or eccentric repetitions at 80% of each subject's
concentric 1 repetition maximum. There was no significant difference
between contraction types for either FSR, FBR, or net balance (FSR
minus FBR). Exercise resulted in significant increases in muscle FSR,
above rest, at all times: 3h = 112%, 24h = 65%, 48h = 34%
(P<0.01). Muscle FBR was also increased by exercise at 3h
(31%; P<0.05) and 24h (18%; P<0.05) post-exercise, but
returned to resting levels by 48h. Muscle net balance was
significantly increased following exercise at all time points (rest =
-0.0573+/-0.003, 3h = -0.0298+/-0.003, 24h = -0.0413+/-0.004, 48h =
-0.0440+/-0.005; means+/-SE in %/h), and was significantly different
from zero at all time points (P<0.05). There was also a
significant correlation between FSR and FBR (r = 0.88,
P<0.001). We conclude that exercise resulted in an increase in
muscle net protein balance, which persisted for up to 48h following
the exercise bout, and was unrelated to the type of muscle
contraction performed.
Received 16 December 1996; accepted in final form 27 February
1997.
APS Manuscript Number E614-6.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 12 March 1997