Introduction
Investigations into the adaptations of the muscu-
loskeletal and cardiovascular systems to exercise
training have taken precedence in exercise
science research, with very few controlled
studies of the effects of exercise on gastrointesti-
nal function. Nevertheless, there is a wealth of
knowledge of normal gastrointestinal function
which is pertinent to the design of an optimal
nutritional plan for those actively engaged in
sport. There is also a growing body of knowledge
concerning alterations in gastrointestinal func-
tion as a result of exercise. The focus of this
review is to highlight those aspects of gastroin-
testinal function and dysfunction to give a basis
for nutritional supplementation regimens and to
gain an understanding of the causative factors
involved in the development of gastrointestinal
symptoms as a result of exercise.
Normal gastrointestinal function and
the effects of exercise
Oesophageal function
The tone of the lower oesophageal sphincter is
of primary importance for the maintenance of a
unidirectional flow of fluids and nutrients
through the digestive tract. Several studies have
examined the effects of exercise on this sphincter.
In one study by Worobetz and Gerrard (1986), 1 h
of treadmill running at 50% of V
.
o2max.resulted in
an increase of the lower sphincter pressure from
a baseline of 24 mmHg to 32 mmHg in asympto-
matic, trained individuals. Oesophageal peris-
talsis, however, remained unchanged. Another
study, however, found a decrease in lower
oesophageal sphincter pressure and an increase
in disordered motility with intensive exercise
compared with rest (Peters et al. 1988). This
is supported by a more recent study by Soffer
et al. (1993), who demonstrated decreasing
oesophageal peristalsis with increasing cycling
intensity from rest to 60% to 75% to 90% of
V.
o2peakin trained subjects. The duration, ampli-
tude and frequency of oesophageal contractions
all declined with increasing intensity. The
number of gastro-oesophageal reflux episodes
and the duration of acid exposure were signifi-
cantly increased at 90% V.
o2peak. Another study
by the same authors (Soffer et al. 1994) demon-
strated similar results with untrained subjects.
Again, subjects cycled at graded intensities
from 60% to 90% of V.
o2peakand a decrease in
oesophageal persitalsis with increasing intensity
was observed. Also, an increase in the number
and duration of reflux episodes and acid expo-
sure was observed during cycling at 90% of
V.
o2peakas with trained subjects.
The discrepancy between the results obtained
by Worobetz and Gerrard (1986) and those of the
others may be explained by a differential effect of
exercise intensity. It may be that a relatively mild
exercise bout, for those accustomed to training
at a higher intensity, may decrease the lower
oesophageal tone. Beyond a certain relative
intensity, an inverse effect may occur. This idea of