Amino acid metabolism, branched-chain amino acid feeding and brain monoamine function

Several papers in the present symposium emphasize the importance and interplay of carbohydrate and fat metabolism during exercise of varying intensities and duration. In constrast, amino acid metabolism is deemed to make only a minimal contribution to the provision of energy for the working muscle and is, with few exceptions, ignored. Equally, the mechanisms of what is termed ‘central fatigue’, i.e. fatigue associated with alterations in the functioning of the brain or central nervous system (CNS), are largely unexplored. However, several papers over the past few years have promoted an attractive role for certain amino acids as substrates for intermediary metabolism and precursors of brain neurotransmitters. The focus of the present paper is the potential interplay between peripheral substrate utilization, amino acid metabolism, brain neurotransmitter function and fatigue. For the purpose of the present symposium only experimental data obtained from human subjects will be considered.