EFFECTS OF INGESTED FLUIDS ON EXERCISE CAPACITY AND ON CARDIOVASCULARAND METABOLIC RESPONSES TO PROLONGED EXERCISE IN MAN

It is well established that the ingestion of carbohydrate-containing d rinks can improve the performance of prolonged exercise. The present s tudy examined the effects of ingestion of water and two dilute glucose -electrolyte drinks on exercise performance and on cardiovascular and metabolic responses to exercise. Twelve subjects exercised to exhausti on on a cycle ergometer at a workload corresponding to 70% of maximum oxygen uptake (V-O2 max) on five occasions each separated by 1 week. T he first trial served to accustom subjects to experimental conditions. On one trial, no drinks were given and on the others subjects drank 1 00 ml every 10 min. Drinks consisted of water, an isotonic glucose-ele ctrolyte solution (I: 200 mmol/l glucose, 35 mmol/l Na+; 310 mosmol/kg ) and a hypotonic glucose-electrolyte solution (H: 90 mmol/l glucose; 60 mmol/l Na+, 240 mosmol/kg). Treatment order was randomized. Blood a nd expired air samples were taken and heart rate and rectal temperatur e measured at intervals during exercise. Median exercise time was grea test for treatment H (110.3 min) followed by treatment I (107.3 min), water (93.1) and no drink (80.7). Endurance times differed significant ly overall, and for pairwise comparisons (P < 0.01) between the no-dri nk trial and both treatments H and I: a difference between water and n o drink was seen at the 5% level. At exhaustion, a significant treatme nt difference was found for the change in plasma volume, with the grea test decrease (6.7%) on the no-drink trial and the smallest decrease ( 0.5%) on treatment H. Significant treatment effects were also observed for heart rate, rectal temperature and serum osmolality. The results suggest that the ingestion of glucose-electrolyte drinks can improve e xercise performance even when the amount of added glucose is small, an d that performance may also be enhanced, albeit to a lesser degree, by ingestion of water.