Effects Of Acute Versus Passive Drinking On Body Fluid Balance During Exercise In Heat

Abstract

PURPOSE: This study examined the effect of active vs. passive drinking practices during exercise training sessions on the fluid balance during exercise in a hot environment. METHODS: Nine healthy men (24.7±3.1 yrs, 174.8±4.6 cm, 73.1±6.5 kg, 14.1±3.7 %fat) completed two experiments separated by one month. Each experiment consisted of three phases; pre-testing (pre), training phase, and post-testing (post). During testings, subjects ran on a treadmill at 66±3% of VO2max for 90 min at 39±1°C and 65±3% relative humidity followed by a three-hour recovery. They drank ad libitum during testings. In training phases, they ran on a treadmill for 70 min at the identical environmental conditions as the testing for seven days while either drinking sports drink actively (AD, 150% of weight loss by exercise) or passively (PD, 50% of weight loss). During testings, urine specific gravity (USG), naked weight change, amount of fluid consumption, sweat loss (SL), relative change of plasma volume (%PV), and rectal temperature (Tre) were measured. RESULTS: Before testing, USG was not different among conditions. During running in testing, they drank more in post-AD (1592±953) than in pre-AD (855±551) (P<0.05), while not different between post-PD (1166±714) and pre-PD (1050±913 ml). The amount of fluid intake during recovery was not different between AD and PD. The SL was greater in post-AD (1377±956) than in pre-AD (558±642) (P<0.05) but not different in PD (900±802 vs. 798±984 ml, respectively). During recovery, SL was greater in post-AD (2114±719) than in pre-AD (1122±731) (P<0.05), but not in PD (1780±1018 vs. 1668±1046 ml, respectively). During running, Tre increased 2.6-3.2°C, but was not different among conditions. The loss of fluid during recovery was greater in post-AD than in pre-AD (P<0.05). The %PV was not different between running in post-PD than post-AD (P<0.05). CONCLUSIONS: Active drinking during training resulted in a greater fluid intake and sweating during exercise in the heat, but a negative fluid balance was also greater in active drinking condition during recovery. (This study was partially supported by Gatorade Company.)