Effect of exercise on concentrations of free amino acids in pools of type I and type II fibres in human muscle with reduced glycogen stores

Authors

  • B. ESSÉN-GUSTAVSSON,

    1. Department of Large Animal Clinical Sciences, Swedish University of Agricultural Sciences, Uppsala, Sweden,
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  • E. BLOMSTRAND

    1. Department of Health and Sport Sciences, University College of Sports and Exercise, Stockholm, Sweden,
    2. Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden
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Dr Birgitta Essén-Gustavsson Department of Large Animal Clinical Sciences, Faculty of Veterinary Medicine, Swedish University of Agricultural Sciences, S-750 07 Uppsala, Sweden.

Abstract

A few animal studies have shown that some amino acid concentrations vary between different muscle fibre types. In the present study, amino acid concentrations were measured in separate pools of different fibre types in human skeletal muscle, with reduced glycogen stores, before and after sustained exercise. Five subjects exercised at a submaximal work rate for 60 min and then at a maximal rate for 20 min. Biopsy samples were taken from the vastus lateralis muscle before and after exercise; they were freeze-dried and individual fibres were dissected out. Fragments of these fibres were stained for myosin-adenosine triphosphatase (ATPase) and identified as type I or type II fibres. The concentrations of free amino acids were measured by high performance liquid chromatography (HPLC) in perchloric acid (PCA) extracts containing pools of either type of fibre. After exercise, glycogen was decreased in type I fibres (53%) and in four subjects also in type II fibres. The concentrations of most amino acids were similar in the two fibre types before exercise, but the glutamate, aspartate and arginine levels were 10% higher in type II than in type I fibres. After exercise, the glutamate concentration was decreased by 45% in both fibre types and the branched-chain amino acids (BCAA) were decreased in type II fibres (14%). Exercise caused an increase by 25–30% in tyrosine concentration in both type I and type II fibres. The results show that amino acids can be measured in pools of fibre fragments and suggest that amino acid metabolism play an important role in both type I and type II fibres during exercise.

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