Plasma Volume Responses Associated with a Sprint Triathlon in Novice Triathletes

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