Abstract
A group of 114 previously untrained subjects, 31 females and 83 males, was followed
for 18 months while training for a marathon. Forty-four of the subjects completed
a survey regarding fluid intakes and gastrointestinal (GI) disturbances during competition
for both their first 25-km race (run after 1 year of training) and their first marathon.
GI problems were common. Among the individuals surveyed, 25% had GI complaints in
the 25-km race. In the marathon, 52% complained of GI distress. In general, fluid
consumption was low (25 km x̄ = 109 ml; marathon w = 577 ml). Body weight losses in
the marathon were substantial (w = 3.2%, BW; range 1.5%-6.2%) indicating sweat losses
greater than fluid replacement. These losses were greater in men than in women (men
w = 3.4% BW; women w = 2.6% BW). GI complaints were not associated with larger drink
intakes. In contrast, dehydration above a certain limit appears to increase the frequency
of GI disorders. In the marathon, 80% of the runners who lost > 4% BW had GI problems.
It is possible that reduced blood flow to the GI region is compromised via the exercise
itself as well as by a reduced blood volume, which may disrupt normal secretion/absorption
of the digestive tract. It may also be that a rising core body temperature, associated
with decreased sweating at high levels of dehydration, may be related to GI dysfunction.
Key words
marathon - gastrointestinal function - dehydration
