Introduction
Amino acids and the athlete
This chapter discusses the importance of some
amino acids in relation to exercise, in par-
ticular to prolonged, exhaustive exercise. Protein
metabolism and the protein requirements of
the athlete have already been discussed in
Chapter 10. Nevertheless, it is worth mentioning
here that consideration of daily protein require-
ments is complicated by the fact that not all
proteins in the diet have the same nutritional
value, since they contain different amounts of
essential amino acids. First-class proteins (e.g. in
eggs, milk and meat) contain enough of each
essential amino acid to allow protein synthesis to
occur without the need to eat extra protein (Fig.
11.1).
By contrast, proteins of plant origin are termed
‘second class’ because they are deficient in the
same amino acids. Adequate amounts of each of
the essential amino acids can be obtained from a
vegetarian diet by eating a wide range of plant
foods, e.g. cereals and legumes. This does mean,
however, that the extra protein consumed takes
the place in the diet of the all-important carbohy-
drate. The athlete must therefore seek a balance:
too much protein and the diet is distorted; too
little and recovery after intensive training might
be slowed. This problem leads to a consideration
of supplementation of the diet with essential
amino acids, especially during peak training.
Furthermore, from studies on individual cells
in vitro, knowledge is becoming available of the
individual nutritional requirements of particular
cells and how these change under different con-
ditions. Transfer of this knowledge to clinical
situations has occurred over the past 10 years
with considerable success. Consequently, it is
now possible to provide nutrients designed to
deliver fuels to particular cells, tissues and
organs that are involved in the response to injury
or illness, and this will enhance the natural
healing process.
This information can be extended to include
the athlete. Furthermore, a specific response to
exercise, and to physical and mental fatigue, can
provide information that could be applied in the
clinic. In addition, it is possible to suggest some
amino acids with which athletes might consider
supplementing their diet (Table 11.1). Some of
the acquired non-dispensable amino acids that
might be of benefit to athletes if taken as a
supplement have been discussed elsewhere
(Newsholmeet al.1994). In this chapter discus-
sion will centre on glutamine and the branched
chain amino acids, for which evidence of benefit
in the athletic field is available.Fatigue in physical activity
Fatigue in physical activity can be considered at
physiological or biochemical levels. Potential
mechanisms for fatigue at a physiological level
are as follows (see Fitts 1994).
1 Central fatigue:
(a) excitatory input to higher motor centres;