2007, Piran, Slovenia

Non-thermal factors
A tendency for thirst in exercise to show Fitness differences across Hydration (P=0.05) was
attributed to lower thirst by Untrained participants in EUH, because groups had similar thirst
(average rating ~ 5 out of 9) during the dehydration phase of HYPO. Thus, trained
participants were not less thirsty at matched levels of hypohydration and dehydration. When
allowed to drink ad libitum (last 40 min in HYPO) Trained participants tended to ingest more
than did Untrained (1.20 ±0.16 vs 0.88 ±0.16 L; P=0.19), in accordance with their higher
sweat rates, such that end-exercise body mass for both fitness groups were equivalently below
baseline (-2.0 ±0.3% [1.42 L] vs -1.6 ±0.2% [1.28 L]; P=0.39), and similar to the starting
level of -1.8%.
DISCUSSION
Endurance-trained athletes responded to dehydration with equivalent perceptual (thirst) and
behavioural (ad libitum consumption) responses as those of recreationally-active people, and
thus maintained similar fluid balance during exercise. However, the athletes had a lower
neuro-endocrine response ([AVP]plasma) across time and increasing plasma osmolality, which
might reflect a peripheral adaptation, such as increased sensitivity of renal aquaporins to
AVP.
ACKNOWLEDGEMENT
We are thankful to Mrs Karen Brassett for her skilled technical assistance, and to the
participants for their commitment.
265