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  • 1.
    Blomstrand, Eva
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Eva Blomstrand's research group.
    Amino acids and central fatigue.2001In: Amino Acids, ISSN 0939-4451, E-ISSN 1438-2199, Vol. 20, no 1, p. 25-34Article in journal (Refereed)
    Abstract [en]

    There is an increasing interest in the mechanisms behind central fatigue, particularly in relation to changes in brain monoamine metabolism and the influence of specific amino acids on fatigue. Several studies in experimental animals have shown that physical exercise increases the synthesis and metabolism of brain 5-hydroxytryptamine (5-HT). Support for the involvement of 5-HT in fatigue can be found in studies where the brain concentration of 5-HT has been altered by means of pharmacological agents. When the 5-HT level was elevated in this way the performance was impaired in both rats and human subjects, and in accordance with this a decrease in the 5-HT level caused an improvement in running performance in rats. The precursor of 5-HT is the amino acid tryptophan and the synthesis of 5-HT in the brain is thought to be regulated by the blood supply of free tryptophan in relation to other large neutral amino acids (including the branched-chain amino acids, BCAA) since these compete with tryptophan for transport into the brain. Studies in human subjects have shown that the plasma ratio of free tryptophan/BCAA increases during and, particularly, after sustained exercise. This would favour the transport of tryptophan into the brain and also the synthesis and release of 5-HT which may lead to central fatigue. Attempts have been made to influence the 5-HT level by giving BCAA to human subjects during different types of sustained heavy exercise. The results indicate that ingestion of BCAA reduces the perceived exertion and mental fatigue during exercise and improves cognitive performance after the exercise. In addition, in some situations ingestion of BCAA might also improve physical performance; during exercise in the heat or in a competitive race when the central component of fatigue is assumed to be more pronounced than in a laboratory experiment. However, more experiments are needed to further clarify the effect of BCAA and also of tryptophan ingestion on physical performance and mental fatigue.

  • 2.
    Blomstrand, Eva
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Eva Blomstrand's research group.
    Essén-Gustavsson, Birgitta
    Changes in amino acid concentration in plasma and type I and type II fibres during resistance exercise and recovery in human subjects.2009In: Amino Acids, ISSN 0939-4451, E-ISSN 1438-2199, Vol. 37, no 4, p. 629-36Article in journal (Refereed)
    Abstract [en]

    Eight male subjects performed leg press exercise, 4 x 10 repetitions at 80% of their maximum. Venous blood samples were taken before, during exercise and repeatedly during 2 h of recovery. From four subjects, biopsies were taken from the vastus lateralis muscle prior to, immediately after and following one and 2 h of recovery. Samples were freeze-dried, individual muscle fibres were dissected out and identified as type I or type II. Resistance exercise led to pronounced reductions in the glutamate concentration in both type I (32%) and type II fibres (70%). Alanine concentration was elevated 60-75% in both fibre types and 29% in plasma. Glutamine concentration remained unchanged after exercise; although 2 h later the concentrations in both types of fibres were reduced 30-35%. Two hours after exercise, the plasma levels of glutamate and six of the essential amino acids, including the branched-chain amino acids were reduced 5-30%. The data suggest that glutamate acts as an important intermediate in muscle energy metabolism during resistance exercise, especially in type II fibres.

  • 3.
    Sahlin, Kent
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Research group for Mitokondriell funktion och metabolisk kontroll.
    Harris, Roger C
    The creatine kinase reaction: a simple reaction with functional complexity.2011In: Amino Acids, ISSN 0939-4451, E-ISSN 1438-2199, Vol. 40, no 5, p. 1363-7Article in journal (Refereed)
    Abstract [en]

    The classical role of PCr is seen as a reservoir of high-energy phosphates defending cellular ATP levels under anaerobic conditions, high rates of energy transfer or rapid fluctuations in energy requirement. Although the high concentration of PCr in glycolytic fast-twitch fibers supports the role of PCr as a buffer of ATP, the primary importance of the creatine kinase (CK) reaction may in fact be to counteract large increases in ADP, which could otherwise inhibit cellular ATPase-mediated systems. A primary role for CK in the maintenance of ADP homeostasis may explain why, in many conditions, there is an inverse relationship between PCr and muscle contractility but not between ATP and muscle contractility. The high rate of ATP hydrolysis during muscle contraction combined with restricted diffusion of ADP suggests that ADP concentration increases transiently during the contraction phase (ADP spikes) and that these are synchronized with the contraction. The presence of CK, structurally bound in close vicinity to the sites of ATP utilization, will reduce the amplitude and duration of the ADP spikes through PCr-mediated phosphotransfer. When PCr is reduced, the efficiency of CK as an ATP buffer will be reduced and the changes in ADP will become more prominent. The presence of ADP spikes is supported by the finding that other processes known to be activated by ADP (i.e. AMP deamination and glycolysis) are stimulated during exercise but not during anoxia, despite the same low global energy state. Breakdown of PCr is driven by increases in ADP above that depicted by the CK equilibrium and the current method to calculate ADPfree from the CK reaction in a contracting muscle is therefore questionable.

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