Effects of ingested fluids on exercise capacity and on cardiovascular and metabolic responses to prolonged exercise in man

Abstract

SUMMARYIt is well established that the ingestion of carbohydrate-containing drinks can improve the performance of prolonged exercise. The present study 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 exhaustion on a cycle ergometer at a workload corresponding to 70 % of maximum oxygen uptake (VO2max) on five occasions each separated by 1 week. The first trial served to accustom subjects to experimental conditions. On one trial, no drinks were given and on the others subjects drank 100 ml every 10 min. Drinks consisted of water, an isotonic glucose-electrolyte 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 and expired air samples were taken and heart rate and rectal temperature measured at intervals during exercise. Median exercise time was greatest for treatment H (110.3 min) followed by treatment I (107.3 min), water (93.1) and no drink (80.7). Endurance times differed significantly overall, and for pairwise comparisons (P < 0.01) between the no-drink trial and both treatments H and I: a difference between water and no drink was seen at the 5 % level. At exhaustion, a significant treatment difference was found for the change in plasma volume, with the greatest 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 exercise performance even when the amount of added glucose is small, and that performance may also be enhanced, albeit to a lesser degree, by ingestion of water.

The Effects of Sports Drink Osmolality on Fluid Intake and Immunoendocrine Responses to Cycling in Hot Conditions

“…Maughan et al (9) provided subjects with an isotonic drink (200 mmol/L glucose; 310 mOsm/kg) or a hypotonic drink (90 mmol/L glucose; 240 mOsm/kg) at a rate of 100 mL every 10 min. Similar to the present study, these studies reported no significant differences between the isotonic and hypotonic drink trials in rectal temperature or blood lactate concentrations at the end of exercise (8,9). In contrast with the present study, both studies observed smaller changes in serum osmolality during exercise after consuming the hypotonic drinks compared the isotonic drinks (8,9).…”

“…Similar to the present study, these studies reported no significant differences between the isotonic and hypotonic drink trials in rectal temperature or blood lactate concentrations at the end of exercise (8,9). In contrast with the present study, both studies observed smaller changes in serum osmolality during exercise after consuming the hypotonic drinks compared the isotonic drinks (8,9). Furthermore, Galloway and Maughan (8) found that plasma volume decreased to a smaller extent during exercise when consuming the hypotonic drink compared with the isotonic drink.…”

“…First, drink osmolality influences personal preference for fluid consumption during exercise (7) and exercise-induced changes in plasma volume and serum osmolality (8,9). Personal preference for fluid consumption influences voluntary fluid intake and changes in body temperature during exercise (10), which may in turn affect immunoendocrine responses to exercise (11)(12)(13)(14)(15).…”

Nutra-ergonomics: influence of nutrition on physical employment standards and the health of workers

“…It is well evidenced that there is a difference in physiological stress between euhydrated and dehydrated individuals, with several reviews indicating minimal dehydration (as low as 1%-2% body mass loss) potentially affecting mood, attention, reaction time, vigilance, working memory, and increased tension/anxiety (American Dietetic Association 2009; Ganio et al 2011;Masento et al 2014;Maughan 2003;Maughan et al 2007). Moderate dehydration (ϳ2% body mass loss) has commonly been associated with detrimental physiological effects and reductions in endurance exercise performance, particularly in hot conditions (Burge et al 1993;Ebert et al 2007;Lopez et al 2011;Maughan et al 1996;McConell et al 1997;Sawka et al 2007). Therefore, hydration needs to be considered across a spectrum of professions.…”

Thermoregulation in hypertensive men exercising in the heat with water ingestion

“…Moreover, there are only a few studies with hypertensive individuals exercising in a hot environment (5,8) and the question remains if arterial hypertension would cause any impairment of cardiovascular and thermoregulatory responses to exercise in a hot environment. Indeed, fluid ingestion before and during exercise is recommended to maintain a normal hydration status in healthy people and to attenuate the rise in core temperature (9), as well as to decrease the risk of hyperthermia, to maintain the performance level and to delay fatigue (2,(10)(11)(12)(13)(14)(15)(16). It is known that arterial hypertension is accompanied by disturbances in fluid balance, a fact raising the question whether fluid ingestion and replacement schedules should be applied to hypertensive and normotensive individuals (17).…”