The effect of glycerol and desmopressin on exercise performance and hydration in triathletes.
BACKGROUND
Hydration is an important determinant of athletic performance, and glycerol-containing solutions have been demonstrated to produce a state of hyperhydration. Secretions of arginine vasopressin (AVP) and/or other renal mechanisms may account for reduced urine output following glycerol ingestion. This study examined the effect of glycerol and the AVP analog desmopressin (DDAVP) on hydration and exercise performance in triathletes ingesting routine volumes of prerace fluids.


METHODS
Eight male triathletes ages 19 to 43 participated. After determination of their VO(2peak), each athlete completed a strenuous exercise protocol three times involving 60 min of exercise at 70% VO(2peak) followed immediately by an incremental increase in workload every 2 min until exhaustion.


RESULTS
Pretreatment with 1 gxkg(-1) glycerol or 20 microgram of DDAVP intranasally failed to produce hyperhydration or any enhancement of athletic performance. There was a significant difference in reduction in body mass between DDAVP and control (P < 0.05) but no change in sweat volume. No physiologically relevant differences in plasma sodium, renin, or hemoglobin were seen with either active agent. Plasma osmolality did have a different time course in response to exercise following glycerol (P < 0.03) owing to a smaller incremental increase. Urine osmolality was also raised at baseline following glycerol (P < 0.05). Responses to exercise of plasma AVP, cortisol, and indices of carbohydrate metabolism were similar, although AVP was elevated following DDAVP administration (P < 0.01) owing to assay cross-reactivity.


CONCLUSIONS
Although maintaining adequate hydration remains important for the endurance athlete, the routine use of either glycerol of DDAVP before athletic training or competition in a thermoneutral environment does not seem to confer any advantage over conventional fluid replacement.
Department of Endocrinology, Christchurch Hospital, New Zealand.
W J
WJ
Inder
M P
MP
Swanney
R A
RA
Donald
T C
TC
Prickett
J
J
Hellemans
D000328:Adult; D001786:Blood Glucose / Q000032:analysis; D001834:Body Water / Q000187:drug effects*; D003894:Deamino Arginine Vasopressin / Q000494:pharmacology*; D015444:Exercise / Q000502:physiology*; D005934:Glucagon / Q000097:blood; D005990:Glycerol / Q000494:pharmacology*; D006801:Humans; D007328:Insulin / Q000097:blood; D008297:Male; D010101:Oxygen Consumption; D012076:Renal Agents / Q000494:pharmacology*; D013546:Sweating
D001786:Blood Glucose; D007328:Insulin; D012076:Renal Agents; D005934:Glucagon; D003894:Deamino Arginine Vasopressin; D005990:Glycerol