Abstract
Short-course triathlons have recently become popular in Australia, especially with
novice athletes as a lead up to the longer versions. This study investigated the changes
that occurred in plasma volume of novice triathletes undertaking their first competitive
triathlon. Ten males participated in the event which took place on a cool, overcast
day and consisted of a 1.0-km swim, a 30-km cycle ride, and a 10-km run. The subjects
were all well trained with V̇O2max values of 53.2±6.1 ml O2·kg-1·min-1. A control experiment was also conducted with the athletes spending the same time
resting in the same position as they did while competing in the event. Blood was drawn
and analyzed for hemoglobin and packed cell volume.
The time for completion of the triathlon was 134.8±6.9 min, with the swim stage being
25.2±5.7 min, the cycle stage 60.9±7.1 min, and the running stage 48.7±6.6 min. Weight
decreased significantly (P < 0.01) during the event from a preevent high of 71.7±7.9 kg to a post-event low
of 70.3±7.6 kg. Plasma volume during the triathlon by 14.3%±1.8% (P < 0.001), but during the control trial by only 5.2%±1.6%. The difference of 9.1%±1.7%
can be attributed to the effects of exercise on plasma volume rather than an effect
of posture. The major decrease in plasma volume was during the running stage of the
triathlon during which it decreased by 6.2%±1.7%, of which 3.0%±1.8% was attributable
to exercise alone. An interesting finding was the hemodilution that occurred during
the immersion rest phase, 3.6%±1.3%(P < 0.05).
Novice triathletes find the sprint triathlon stressful and the loss of plasma volume
is significant. Clearly, care needs to be taken to ensure that such races are conducted
such that athletes have plenty of fluids available especially during hot and humid
conditions.
Key words
Plasma volume - mean aterial pressure - sprint triathlon
