a U-shaped relationship between exercise inten-
sity and digestive processes is in line with early
advice, based on anecdotal evidence, to perform
mild exercise after a meal to facilitate digestion.
There is some evidence to support the idea that
this type of curvilinear relationship also exists
between exercise intensity and gastric emptying.
Schoeman and coworkers (1995) also looked at
the effects of standardized meals and standard-
ized exercise on lower oesophageal pressure and
reflux. It was found that the timing of the meal
had a greater effect on the incidence of reflux
than did exercise. Sixty-six per cent (81 of 123) of
reflux episodes occurred within 3 h after food
intake, but only two episodes occurred during
exercise. A number of other factors, including
fat, alcohol, coffee ingestion and smoking also
reduce sphincter pressure.
Gastric emptying
Early observations of gastric function were made
in which an inhibitory effect of emotional stress
on gastric emptying rate was documented
(Beaumont 1838). In another early study, Camp-
bellet al. (1928) demonstrated that physical stress
also decreased gastric emptying. Costill and
Saltin (1974) showed that 15 min of cycling above
70% of V
.
o2max.decreased gastric emptying of a
carbohydrate- and electrolyte-containing fluid,
but that exercise at a lower intensity did not
affect the emptying rate. It is, however, only in
the last decade that a larger number of studies
have been conducted to assess the effects of exer-
cise on gastric function. In contrast to most of the
early work, exercise intensity has been more
closely controlled and clearly defined.
There is some disparity in results with regard
to the effects of low- to moderate-intensity exer-
cise on the gastric emptying rate. Neufer and
colleagues (1989b) found an increased gastric
emptying rate with exercise of a low to moderate
intensity, with both walking (28%, 41% and 56%
ofV
.
o2max.) and running (57% and 65% of V.
o2max.)
when compared with rest. They also showed a
decrease in emptying with intensive exercise
242 nutrition and exercise
(75% of V.
o2max.). Marzio et al. (1991) also exam-
ined the effects of mild (50% max HR) and stren-
uous (70% max HR) treadmill exercise on gastric
emptying. Their data support those of Neufer in
that the gastric emptying was accelerated with
mild exercise but delayed with more strenuous
exercise. Research by Sole and Noakes (1989) also
demonstrated a decreased emptying of water
with exercise at 75% of V.
o2max.compared with
rest, but there was no effect of exercise on the
emptying of a 10% carbohydrate beverage. Since
it is known that increasing carbohydrate concen-
tration decreases the gastric emptying rate (Vist
& Maughan 1994), one may speculate that this
effect overshadowed any exercise-induced inhi-
bition of gastric function. Other researchers have
failed to find a significant difference at moderate
intensities (50% and 70% of V.
o2max.), although
trends towards slowing have been observed
(Rehrer et al. 1989), while others have shown a
consistently increasing inhibition with moderate
through to intensive (42%, 60% and 80% V.
o2max.)
exercise (Maughan et al. 1990).
Some of the variance in results may be attrib-
uted to the testing protocol. In Neufer’s work,
gastric emptying was measured at a single time
point, after 15 min of exercise, by aspirating the
amount of beverage remaining. Marzio’s experi-
mental design entailed 30 min of exercise fol-
lowed by ingestion of a beverage and thereafter
following emptying with ultrasonography and
scintigraphy. Rehrer and coworkers (1989) used
a repeated, dye-dilution, sampling technique in
which comparisons were made at frequent inter-
vals over a period of 1 h, representing the com-
plete emptying curve of a beverage ingested at
the onset of exercise. Maughan and coworkers’
research (1990) was also done with multiple
measurement points over a complete emptying
curve. They, however, measured blood accu-
mulation of a deuterium tracer added to the
ingested drink, which represents the effects of
both gastric emptying and intestinal absorption.
Nevertheless, both methods in which measure-
ments were made at multiple points, over a
longer exercise time, with beverage ingestion