The aim of this study was to investigate whether prolonged one-leg knee-extensor exercise enhances net protein degradation in muscle with a normal or low glycogen content. Net amino acid production, as a measure of net protein degradation, was estimated from leg exchange and from changes in the concentrations of amino acids that are not metabolized in skeletal muscle. Experiments were performed at rest and during one-leg knee-extensor exercise in six subjects having one leg with a normal glycogen content and the other with a low glycogen content. Exercise was performed for 90 min at a workload of 60–65% of maximal one-leg power output, starting either with the normal-glycogen or the low-glycogen leg, at random. The net production of threonine, lysine and tyrosine and the sum of the non-metabolized amino acids were 9–20-fold higher (P< 0.05) during exercise of the normal-glycogen leg than at rest. Total amino acid production was also 10-fold higher during exercise compared with that at rest (difference not significant). The net production rates of threonine, glycine and tyrosine and of the sum of the non-metabolized amino acids were about 1.5–2.5-fold higher during exercise with the leg with a low glycogen content compared with the leg with a normal glycogen content (P< 0.05). Total amino acid production was 1.5-fold higher during exercise for the low-glycogen leg compared with the normal-glycogen leg (difference not significant). These data indicate that prolonged one-leg knee-extensor exercise leads to a substantial increase in net muscle protein degradation, and that a lowering of the starting muscle glycogen content leads to a further increase. The carbon atoms of the branched-chain amino acids (BCAA), glutamate, aspartate and asparagine, liberated by protein degradation, and the BCAA and glutamate extracted in increased amounts from the blood during exercise, are used for the synthesis of glutamine and for tricarboxylic-acid cycle anaplerosis.
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September 17 1999
Muscle protein degradation and amino acid metabolism during prolonged knee-extensor exercise in humans
G. VAN HALL;
*Department of Human Biology, Maastricht University, Maastricht, The Netherlands
Correspondence: G. van Hall, Copenhagen Muscle Research Centre, Rigshospitalet, section 7652, Tagens vej 20, 2200 Copenhagen N, Denmark (e-mail [email protected]).
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B. SALTIN;
B. SALTIN
†Copenhagen Muscle Research Centre, Copenhagen, Denmark
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A. J. M. WAGENMAKERS
A. J. M. WAGENMAKERS
*Department of Human Biology, Maastricht University, Maastricht, The Netherlands
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Publisher: Portland Press Ltd
Received:
December 17 1998
Revision Received:
June 01 1999
Accepted:
July 22 1999
Online ISSN: 1470-8736
Print ISSN: 0143-5221
The Biochemical Society and the Medical Research Society © 1999
1999
Clin Sci (Lond) (1999) 97 (5): 557–567.
Article history
Received:
December 17 1998
Revision Received:
June 01 1999
Accepted:
July 22 1999
Citation
G. VAN HALL, B. SALTIN, A. J. M. WAGENMAKERS; Muscle protein degradation and amino acid metabolism during prolonged knee-extensor exercise in humans. Clin Sci (Lond) 1 November 1999; 97 (5): 557–567. doi: https://doi.org/10.1042/cs0970557
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