The Role of Nutritional Catecholamine Precursors During Prolonged Exercise in the Heat

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Student thesis: Doctoral ThesisDoctor of Philosophy

Original languageEnglish
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Award date23 Apr 2012
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Abstract

An emerging hypothesis states that brain catecholamine availability is directly related to tolerance of prolonged exercise in the heat. The aim of this thesis was to nutritionally alter the plasma availability of the catecholamine precursors, tyrosine and phenylalanine, to explore the effect on prolonged exercise (whole body and single limb) in the heat, including cycling capacity and performance.

In study 1 (Chapter 3) acutely increasing the plasma ratio of tyrosine:large neutral amino acids (LNAA; the tyrosine ratio) via oral ingestion of 150 mg·kg body mass-1 tyrosine increased exercise capacity in the heat. The increase was seemingly related to a lower rate of core temperature (Tcore) increase and/or reduced RPE and thermal sensation late in exercise. Exercise capacity in the heat was markedly reduced when subjects were acutely administered a tyrosine and phenylalanine-free amino acid mixture which decreased the tyrosine ratio (study 2, Chapter 4), and the reduction seemed to be related to a more rapid attainment of maximal RPE, thermal sensation and heart rate. Acute tyrosine supplementation failed to improve simulated time trial performance in the heat (study 3, Chapter 5). This may be due to a lower physiological and subjective demand inherent in the self-paced nature of the exercise, in comparison to an exhaustive capacity trial. In study 4 (Chapter 6), acute tyrosine supplementation had no effect on sustained handgrip force, heart rate variability, or mood and motivation scores, when subjects were hyperthermic.

The studies within this thesis provide further insight into the aetiology of central fatigue during prolonged exercise in the heat, and suggest that nutritional catecholamine precursor availability is involved, in part, in this process. In particular, an increased availability of nutritional catecholamine precursors, reported for the first time herein, may afford improved tolerance of prolonged, constant-load, submaximal activity in the heat.

Keywords

  • prolonged exercise, amino acids, hyperthermia, tyrosine, phenylalanine, catecholamines

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