One of the challenges in maintaining focus during intense
training and physical exercise is mental fatigue. Whereas most
athletes worry about and take corrective action to ward against
muscle fatigue, mental fatigue must be combated as well. In
fact, recent research has placed increasing emphasis on mental
fatigue during exercise. This mental fatigue is commonly
referred to as central fatigue because of the involvement of the
central nervous system. While central fatigue does not affect
muscles, it can reduce the capacity to perform optimally. There
is a correlation between the amino acid tryptophan in the brain
and the degree of mental fatigue. Upon entry into the brain,
tryptophan has the ability to ''calm'' the central nervous
system, causing sleep and drowsiness. Normally, there are
sufficient amounts of branched-chain amino acids (BCAAs)
circulating in the bloodstream to control the entry of
tryptophan into the brain. During long-term and sustained
exercise, however, muscles use large amounts of amino ac