This study investigated the influence of drink carbonation and carbohy
drate content on ad libitum drinking behavior and body fluid and elect
rolyte responses during prolonged exercise in the heat. Eight competit
ive male runners completed three 2-hr treadmill runs at 60% VO2max in
an environmental chamber maintained at 30-degrees-C and 40% RH. Three
test drinks were used: 8% carbohydrate, low carbonation (8%-C); 8% car
bohydrate, noncarbonated (8%-NC), and water (0%-NC). Blood samples wer
e taken preexercise (0), at 60 and 120 min of exercise, and at 60 min
of recovery (+60 min). The data suggest that while reports of heartbur
n tend to be higher on 8% carbohydrate drinks than on 0%-NC, this does
not appear to be a function of drink carbonation. Similarly, the incr
eased frequency of heartburn did not significantly reduce fluid consum
ption either during exercise or during a 60-min recovery period. Impor
tantly, no differences were observed between fluid and electrolyte, or
thermoregulatory responses to the three sport drinks. Thus, consumpti
on of low-carbonation beverages does not appear to significantly influ
ence drinking behavior or the related physiological responses during p
rolonged exercise in the heat.