Physiological risks during a marathon; the influence on thermoregulation and fluid balance.

Recent editions of big running-events ( dam tot dam run, the marathons in
Boston, London and Rotterdam) have suffered of a large quantity of participants
that needed hospitalization, mainly because of heat-related problems. Because
of that, the physiology department of the Radboud university has done large
studies to examine physiological changes during endurance excercise. The most
import results were that 25 percent of the participants to the 4-day march in
Nijmegen showed a significant change in hydratation state and electrolyte
concentrations. In another study we found that 15 percent of the participants
of a 15 km run suffered of hyperthermia. The marathon is an event which is an
extreme endurance race on a high intensity. That combination makes it a
potential dangerous excercise, because both physiological processes
(thermoregulation and water balance) can reach extreme values. Although
several studies have been performed in a marathon setting, those have a limited
value, because of the small group sizes, homogeneous (well-trained men or
women) group-characteristics, its laboratory setting, or temperature
measurements using a rectal thermometer. The population of marathon-runners is
a heterogeous group of trained, untrainend, healthy people and participants
with a history of diseases. Therefore previous results cannot be extrapolated
to an event like the marathon.

To monitor the thermoregulatory reponse and the disturbances of the fluid- and
electrolyte balance during a marathon. Moreover the incidence of hyperthermia
and dehydration is determined, whilst the fluid balance of participants with
and without hyperthermia will be compared.

Observational

In addition to a questionnaire, heart rate monitor and determination of body
weight, subjects receive a sensor pill that record core body temperature. The
latter assessment is a safe, valid and 'friendly' method to record core body
temperature. Furthermore blood and urine will be taken to gain insight into the
fluid and electrolytebalance and measure the Hematocrit and Hemoglobine
concentration. This will be performed by experienced people, which willl
minimise the risk of this action. The burden of these tests are, physical as
well as in time, minimal and provide important information which is necessary
for the primary aim of the study.