The purpose of this study is to summarize water, carbohydrate (CHO), and electrolyte absorption from carbohydrate- electrolyte (CHO-E) solutions based on all of the triple-lumen-perfusion studies in humans since the early 1960s. The current statistical analysis included 30 reports from which were obtained information on water absorption, CHO absorption, total solute absorption, CHO concentration, CHO type, osmolality, sodium concentration, and sodium absorption in the different gut segments during exercise and at rest. Mean differences were assessed using independent-samples t tests. Exploratory multiple-regression analyses were conducted to create prediction models for intestinal water absorption. The factors influencing water and solute absorption are carefully evaluated and extensively discussed. The authors suggest that in the human proximal small intestine, water absorption is related to both total solute and CHO absorption; osmolality exerts various impacts on water absorption in the different segments; the multiple types of CHO in the ingested CHO-E solutions play a critical role in stimulating CHO, sodium, total solute, and water absorption; CHO concentration is negatively related to water absorption; and exercise may result in greater water absorption than rest. A potential regression model for predicting water absorption is also proposed for future research and practical application. In conclusion, water absorption in the human small intestine is influenced by osmolality, solute absorption, and the anatomical structures of gut segments. Multiple types of CHO in a CHO-E solution facilitate water absorption by stimulating CHO and solute absorption and lowering osmolality in the intestinal lumen.
Dennis H. Passe, Mary Horn, John Stofan and Robert Murray
Palatability and voluntary intake of 4 beverages commonly available to athletes were compared in a laboratory exercise protocol designed to mimic aerobic training or competitive conditions in which limited time is available for drinking. Diluted orange juice (DOJ), homemade 6% carbohydrate-electrolyte sports beverage (HCE), commercially available 6% carbohydrate-electrolyte sports beverage (CCE), and water (W) were tested. Fifty adult triathletes and runners (34 males, 16 females) exercised for 75 min at 80–85% of age-predicted heart rate, during which time they were given brief access (60 s) to one of the beverages after 30 min and 60 min of exercise. Results indicated that for overall palatability, CCE > W, HCE, DOJ; W > DOJ, and for amount of beverage consumed, CCE > W, HCE, DOJ; HCE > W, DOJ. The palatability of these beverages varied substantially, as did their voluntary intakes during exercise.
Dennis Passe, Mary Horn, John Stofan, Craig Horswill and Robert Murray
This study investigated the relationship between runners’ perceptions of fluid needs and drinking behavior under conditions of compensable heat stress (ambient temperature = 20.5 ± 0.7 °C, 68.9 °F; relative humidity = 76.6%). Eighteen experienced runners (15 men, 40.5 ± 2.5 y, and 3 women, 42 ± 2.3 y) were given ad libitum access to a sports drink (6% carbohydrate-electrolyte solution) at Miles 2, 4, 6, and 8. After the run (75.5 ± 8.0 min), subjects completed questionnaires that required them to estimate their individual fluid intake and sweat loss. Dehydration averaged 1.9% ± 0.8% of initial body weight (a mean sweat loss of 21.6 ± 5.1 mL·kg−1·h−1). Subjects replaced only 30.5% ± 18.1% of sweat loss and underestimated their sweat loss by 42.5% ± 36.6% (P ≤ 0.001). Subjects’ self-estimations of fluid intake (5.2 ± 3.2 mL·kg−1·h−1) were not significantly different from actual fluid intake (6.1 ± 3.4 mL·kg−1·h−1) and were significantly correlated (r = 0.63, P = 0.005). The data indicate that even under favorable conditions, experienced runners voluntarily dehydrate (P ≤ 0.001), possibly because they are unable to accurately estimate sweat loss and consequently cannot subjectively judge how much fluid to ingest to prevent dehydration. This conclusion suggests that runners should not depend on self-assessment to maintain adequate hydration, underscores the need for runners to enhance their ability to self-assess sweat losses, and suggests that a predetermined regimen of fluid ingestion might be necessary if they wish to maintain more optimal hydration.
Flavia Meyer, Oded Bar-Or, Avi Salsberg and Dennis Passe
This study examined changes in children's thirst and drink preferences during exercise-induced hypohydration and their spontaneous rehydration during a 30-min recovery. Twenty-four 9- to 13-year-old children (14 females, 10 males) participated in four intermittent 90-rnin cycling sessions in the heat (
Craig A. Horswill, Dennis H. Passe, John R. Stofan, Mary K. Horn and Robert Murray
We compared ad libitum fluid consumption in adolescent (n = 15) and adult athletes (n = 34) exercising in similar environmental conditions (26.5°C, 27.3% relative humidity) and similar modes and intensities of exercise (80-85% of their age-predicted maximum heart rate). Throughout 1 hr of exercise, participants had access to sports bottles containing a sports drink (6% carbohydrate with electrolytes and identical flavoring). Sweat rate (SR) and percent dehydration were calculated from the change in body weight corrected for urine loss and fluid intake (FI). FI was significantly higher for the adults than for the adolescents. SR was also higher for the adults compared with that of the adolescents. Compared with adults, adolescents had significantly lower FI and SR, the combination of which allowed them to meet their fluid needs more closely during exercise. Minimal voluntary dehydration occurred in either group during exercise, possibly because of the nature of the exercise (noncompetitive) or the beverage characteristics (presence of sodium and sweetness) or availability of the beverage.
Xiaocai Shi, Mary K. Horn, Kris L. Osterberg, John R. Stofan,, Jeffrey J. Zachwieja, Craig A. Horswill, Dennis H. Passe and Robert Murray
This study investigated whether different beverage carbohydrate concentration and osmolality would provoke gastrointestinal (GI) discomfort during intermittent, high-intensity exercise. Thirty-six adult and adolescent athletes were tested on separate days in a double-blind, randomized trial of 6% and 8% carbohydrate-electrolytes (CHO-E) beverages during four 12-min quarters (Q) of circuit training that included intermittent sprints, lateral hops, shuttle runs, and vertical jumps. GI discomfort and fatigue surveys were completed before the first Q and immediately after each Q. All ratings of GI discomfort were modest throughout the study. The cumulative index for GI discomfort, however, was greater for the 8% CHO-E beverage than for the 6% CHO-E beverage at Q3 and Q4 (P < 0.05). Averaging across all 4 quarters, the 8% CHO-E treatment produced significantly higher mean ratings of stomach upset and side ache. In conclusion, higher CHO concentration and osmolality in an ingested beverage provokes stomach upset and side ache.