Effects of different carbohydrate-electrolyte beverages on the appearance of ingested deuterium in body fluids during moderate exercise by humans in the heat

Abstract

To determine whether different forms of glucose (free and polymer) associated with sodium chloride influence the rate of water absorption during exercise in the heat, six men took part in five trials. Each trial included a passive heating session which resulted in a 2% loss of body mass, followed by 1h of treadmill exercise (at 50% of maximal oxygen uptake) in warm conditions (dry bulb temperature 35 degrees C, relative humidity 20%-30%). Immediately before exercise, the subjects were given either no fluid or a volume equal to 50% of the fluid previously lost (about 650 ml), chosen from among four D2O-labelled beverages: mineral water, a 6% glucose-electrolyte solution (GS), a 6% maltodextrin solution and a 6% maltodextrin-electrolyte solution. No significant differences were observed among these various beverages so far as temporal accumulation of deuterium in plasma, sweat and urine was concerned. During GS, the plasma volume was completely restored and the drifts of heart rate and rectal temperature were less marked than during other trials. These results would suggest that rehydration with GS was more efficient, probably because of an internal redistribution of water. The proportion of ingested water was twice as high in sweat as it was in urine. These findings may reflect the essential part played by circulatory adjustments in the transfer of plasma water into sweat and urine.

Accumulation of 2H2O in plasma and eccrine sweat during exercise-heat stress

“…Therefore, 2 H 2 O accumulation in plasma is more likely related to the gastric emptying rate of the ingested fluid (Costill 1990) than to the intestinal absorption rate of that fluid (Davis et al 1988;Gisolfi et al 1990). The present investigation was the first to evaluate the accumulation and time course of 2 H 2 O in both plasma and sweat during exercise-heat stress, at a time point less than 30 min (Koulmann et al 1997). …”

“…The former investigation (Armstrong et al 1987) appeared as a conference abstract, involved only four subjects (i.e., low statistical power) and utilized H 2 18 O as a stable isotope tracer. The latter investigation (Koulmann et al 1997) reported sweat deuterium oxide accumulation at a point 30 min after ingestion, but at no time points prior to 30 min. This hypothetical outcome, if confirmed, would provide novel support for the recommendations of sports medicine, military organizations (Casa et al 2000; Department of the Army and Air Force 2003) and physiologists (Sawka et al 2007) regarding the benefits of drinking before, or soon after exercise begins, in a warm or hot environment.…”

“…However, little is known about the kinetics of water movement from the mouth to eccrine sweat glands (i.e., via the stomach, intestine, blood and interstitial fluid). Indeed, only three previous studies have focused on isotope accumulation in sweat, and it is difficult to formulate meaningful inferences because of a small test subject sample size in one study (Armstrong et al 1987), differences in research questions (Koulmann et al 1997), or the specific tracer utilized (i.e., 2 H 2 18 O; Schoeller et al 1986). Further, none of these studies focused on the time course or isotope kinetics in sweat.…”

“…This means that athletes, laborers, and military personnel do not appreciate the rate at which ingested fluid can move throughout the body. Based on previous stable isotope investigations which involved different research questions (Armstrong et al 1987;Koulmann et al 1997), we hypothesized that ingested water would appear at the skin in less than 15 min. The former investigation (Armstrong et al 1987) appeared as a conference abstract, involved only four subjects (i.e., low statistical power) and utilized H 2 18 O as a stable isotope tracer.…”

Transition duration of ingested deuterium oxide to eccrine sweat during exercise in the heat

“…Only three studies (Armstrong, et al, 2010;Davis et al, 1985;Koulmann, et al, 1997) in the scientific literature have addressed this topic, and none were specifically designed to determine how rapidly ingested water starts to appear as sweat. For example, the seminal study by Armstrong et al (2010) determined fluid kinetics from ingestion to sweat secretion using deuterium oxide (D 2 O) enrichment during an hour of exercise in the heat.…”