Introduction
Exercise can lead to a depletion of the body’s
glycogen stores, particularly those of the liver
and in the exercising muscle, and to the devel-
opment of a body water deficit. This chapter
concerns itself with recovery after exercise: car-
bohydrate replacement during exercise is dis-
cussed in Chapter 8, and fluid replacement
during exercise is described in detail in Chapter
17.
Glycogen depletion results from the mobili-
zation of the stores to provide energy for the
muscular contraction of the exercise, and is a
major factor contributing to fatigue. This has
been discussed in detail in Chapter 6. Depending
on the intensity, frequency and duration of the
exercise sessions, an almost complete emptying
of the glycogen stores in the exercising muscle is
possible.
Dehydration during exercise results largely
from activation of the body’s temperature-
regulating mechanisms, and a state of hypohy-
dration will be incurred if fluid is not ingested to
match the seat loss. In an attempt to dissipate the
heat produced due to the mechanical inefficiency
of exercise, the sweating mechanism may be acti-
vated and the subsequent evaporation of the
water secreted onto the skin surface removes
with it latent heat of evaporation. This has been
discussed in more detail in Chapters 15 and 17.
Water loss from the respiratory tract, from the
gastrointestinal tract and from urine production
all will add to the body’s water loss. Each of these
routes may result in substantial water losses in
some situations, but for most individuals and in
most exercise situations, sweat production will
be the greatest single factor responsible for creat-
ing a situation of hypohydration (Chapter 17).
Sweat production, however, is not a situation of
pure water being secreted onto the skin, but
rather a variety of electrolytes and other sub-
stances are included in the sweat that is secreted.
A general description of the composition of
sweat with regard to its electrolyte content is
given in Chapter 17.Effects of muscle glycogen depletion
and hypohydration
Muscle glycogen depletion
If exercise is undertaken when the muscles are
depleted of their glycogen stores, performance
will be poorer than when the muscle glycogen
stores are optimal. This has been shown to be
true for prolonged exercise of 1–2 h duration
(Costillet al. 1988), for high-intensity exercise
lasting only a few minutes (Maughan & Poole
1981), and will also result in a reduction in the
amount of running done by games players
(Jacobset al. 1982; Bangsbo 1994). In most of these
situations, performance will be closely related to
the size of the glycogen stores at the beginning of
exercise. This has been discussed in detail in
Chapters 5–8.