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Xuguang Zhang, Niamh O’Kennedy and James P. Morton

The provision of exogenous carbohydrate (CHO) in the form of energy gels is regularly practiced among endurance and team sport athletes. However, in those instances where athletes ingest suboptimal fluid intake, consuming gels during exercise may lead to gastrointestinal (GI) problems when the nutritional composition of the gel is not aligned with promoting gastric emptying. Accordingly, the aim of the current study was to quantify the degree of diversity in nutritional composition of commercially available CHO gels intended for use in the global sports nutrition market. We surveyed 31 product ranges (incorporating 51 flavor variants) from 23 brands (Accelerade, CNP, High5, GU, Hammer, Maxim, Clif, USN, Mule, Multipower, Nectar, Carb-Boom, Power Bar, Lucozade, Shotz, TORQ, Dextro, Kinetica, SiS, Zipvit, Maxifuel, Gatorade and Squeezy). Gels differed markedly in serving size (50 ± 22 g: 29–120), energy density (2.34 ± 0.7 kcal/g: 0.83–3.40), energy content (105 ± 24 kcal: 78–204), CHO content (26 ± 6 g: 18–51) and free sugar content (9.3 ± 7.0 g: 0.6–26.8). Most notably, gels displayed extreme variation in osmolality (4424 ± 2883 mmol/kg: 303–10,135) thereby having obvious implications for both GI discomfort and the total fluid intake likely required to optimize CHO delivery and oxidation. The large diversity of nutritional composition of commercially available CHO gels illustrate that not all gels should be considered the same. Sports nutrition practitioners should therefore consider the aforementioned variables to make better-informed decisions regarding which gel product best suits the athlete’s specific fueling and hydration requirements.

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Xiaocai Shi and Dennis H. Passe

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.

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Stephanie Van Biervliet, Jean Pierre Van Biervliet, Karel Watteyne, Michel Langlois, Dirk Bernard and Johan Vande Walle

The study aimed to evaluate the effect of exercise on urine sediment in adolescent soccer players. In 25 15-year-old (range 14.4–15.8 yrs) athletes, urinary protein, osmolality and cytology were analyzed by flow cytometry and automated dipstick analysis before (T0), during (T1), and after a match (T2). All athletes had normal urine analysis and blood pressure at rest, tested before the start of the soccer season. Fifty-eight samples were collected (T0: 20, T1: 17, T2: 21). Proteinuria was present in 20 of 38 samples collected after exercise. Proteinuria was associated with increased urinary osmolality (p < .001) and specific gravity (p < .001). Hyaline and granular casts were present in respectively 8 of 38 and 8 of 38 of the urinary samples after exercise. The presence of casts was associated with urine protein concentration, osmolality, and specific gravity. This was also the case for hematuria (25 of 38) and leucocyturia (9 of 38). Squamous epithelial cells were excreted in equal amounts to white and red blood cells. A notable proportion of adolescent athletes developed sediment abnormalities, which were associated with urinary osmolality and specific gravity.

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Stephen A. Mears and Susan M. Shirreffs

Water intake occurs following a period of high-intensity intermittent exercise (HIIE) due to sensations of thirst yet this does not always appear to be caused by body water losses. Thus, the aim was to assess voluntary water intake following HIIE. Ten healthy males (22 ± 2 y, 75.6 ± 6.9 kg, VO2peak 57.3 ± 11.4 m·kg−1·min−1; mean± SD) completed two trials (7–14 d apart). Subjects sat for 30 min then completed an exercise period involving 2 min of rest followed by 1 min at 100% VO2peak repeated for 60 min (HIIE) or 60 min continuously at 33% VO2peak (LO). Subjects then sat for 60 min and were allowed ad libitum water intake. Body mass was measured at start and end of trials. Serum osmolality, blood lactate, and sodium concentrations, sensations of thirst and mouth dryness were measured at baseline, postexercise and after 5, 15, 30, and 60 min of recovery. Vasopressin concentration was measured at baseline, postexercise, 5 min, and 30 min. Body mass loss over the whole trial was similar (HIIE: 0.77 ± 0.50; LO: 0.85 ± 0.55%; p = .124). Sweat lost during exercise (0.78 ± 0.22 vs. 0.66 ± 0.26 L) and voluntary water intake during recovery (0.416 ± 0.299 vs. 0.294 ± 0.295 L; p < .05) were greater in HIIE. Serum osmolality (297 ± 3 vs. 288 ± 4mOsmol·kg−1), blood lactate (8.5 ± 2.7 vs. 0.7 ± 0.4 mmol·L−1), serum sodium (146 ± 1 vs. 143 ± 1 mmol·L−1) and vasopressin (9.91 ± 3.36 vs. 4.43 ± 0.86 pg·ml−1) concentrations were higher after HIIE (p < .05) and thirst (84 ± 7 vs. 60 ± 21) and mouth dryness (87 ± 7 vs. 64 ± 23) also tended to be higher (p = .060). Greater voluntary water intake after HIIE was mainly caused by increased sweat loss and the consequences of increased serum osmolality mainly resulting from higher blood lactate concentrations.

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João C. Dias, Melissa W. Roti, Amy C. Pumerantz, Greig Watson, Daniel A. Judelson, Douglas J. Casa and Lawrence E. Armstrong

Context:

Dieticians, physiologists, athletic trainers, and physicians have recommended refraining from caffeine intake when exercising because of possible fluid-electrolyte imbalances and dehydration.

Objective:

To assess how 16-hour rehydration is affected by caffeine ingestion.

Design:

Dose–response.

Setting:

Environmental chamber.

Participants:

59 college-age men.

Intervention:

Subjects consumed a chronic caffeine dose of 0 (placebo), 3, or 6 mg · kg−1 · day−1 and performed an exercise heat-tolerance test (EHT) consisting of 90 minutes of walking on a treadmill (5.6 km/h) in the heat (37.7 °C).

Outcome Measures:

Fluid-electrolyte measures.

Results:

There were no between-group differences immediately after and 16 hours after EHT in total plasma protein, hematocrit, urine osmolality, specific gravity, color, and volume. Body weights after EHT and the following day (16 hours) were not different between groups (P > .05).

Conclusion:

Hydration status 16 hours after EHT did not change with chronic caffeine ingestion.

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Stephen A. Mears and Susan M. Shirreffs

Exercising in cold environments results in water losses, yet examination of resultant voluntary water intake has focused on warm conditions. The purpose of the study was to assess voluntary water intake during and following exercise in a cold compared with a warm environment. Ten healthy males (22 ± 2 years, 67.8 ± 7.0 kg, 1.77 ± 0.06 m, VO2peak 60.5 ± 8.9 ml·kg−1·min−1) completed two trials (7–8 days). In each trial subjects sat for 30 min before cycling at 70% VO2peak (162 ± 27W) for 60 min in 25.0 ± 0.1 °C, 50.8 ± 1.5% relative humidity (RH; warm) or 0.4 ± 1.0 °C, 68.8 ± 7.5% RH (cold). Subjects then sat for 120 min at 22.2 ± 1.2 °C, 50.5 ± 8.0% RH. Ad libitum drinking was allowed during the exercise and recovery periods. Urine volume, body mass, serum osmolality, and sensations of thirst were measured at baseline, postexercise and after 60 and 120 min of the recovery period. Sweat loss was greater in the warm trial (0.96 ± 0.18 l v 0.48 ± 0.15 l; p < .0001) but body mass losses over the trials were similar (1.15 ± 0.34% (cold) v 1.03 ± 0.26% (warm)). More water was consumed throughout the duration of the warm trial (0.81 ± 0.42 l v 0.50 ± 0.49 l; p = .001). Cumulative urine output was greater in the cold trial (0.81 ± 0.46 v 0.54 ± 0.31 l; p = .036). Postexercise serum osmolality was higher compared with baseline in the cold (292 ± 2 v 287 ± 3 mOsm.kg−1, p < .0001) and warm trials (288 ± 5 v 285 ± 4 mOsm·kg−1; p = .048). Thirst sensations were similar between trials (p > .05). Ad libitum water intake adjusted so that similar body mass losses occurred in both trials. In the cold there appeared to a blunted thirst response.

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Robyn L. Bowen, J. Harold Adams and Kathryn H. Myburgh

Purpose:

A 29-year-old elite adventure-race athlete presented with a 10-month history of nausea appearing during or after ultraendurance races. The athlete noted recent worsening of symptoms, including lightheadedness, dark rings under the eyes, and weakness as nausea became worse, and was unable to complete races. Possible diagnoses included dehydration or over hydration, renal damage, and gastrointestinal malfunction.

Methods:

The subject (S) and a case-control athlete (C) performed an 11-hour simulated race (field test) ending in the laboratory. Blood samples were drawn, and body mass and food and drink ingested were noted at regular intervals.

Results:

Symptoms were replicated in S, whose vomitus contained undigested solids consumed during exercise. Over 11 hours, fl uid loss was similar in S (9.6 L) and C (10.3 L), but fluid intake for S was 4.8 L versus 9.9 L for C. Body mass decreased 6% in S and 1.8% in C. S presented with elevated serum urea and creatinine before and after and elevated osmolality after the field test. A week after the fi eld test, creatinine clearance was low in S but not C (83 vs 160 mmol per 24-hour urine, respectively). S was instructed to increase fluid intake throughout the day, to match fluid lost during training, and to refrain from long races. After 2 months, his serum urea, creatinine, and osmolality were normal, and creatinine clearance improved to 133 mmol per 24-hour urine. He repeated the fi eld test and experienced no nausea.

Conclusions:

Nausea in ultraendurance athletes might be an early symptom of chronic but reversible renal strain or insensitivity to high osmolality.

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Robert G. Hahn and Nana Waldréus

Purpose:

Urine sampling has previously been evaluated for detecting dehydration in young male athletes. The present study investigated whether urine analysis can serve as a measure of dehydration in men and women of a wide age span.

Methods:

Urine sampling and body weight measurement were undertaken before and after recreational physical exercise (median time: 90 min) in 57 volunteers age 17–69 years (mean age: 42). Urine analysis included urine color, osmolality, specific gravity, and creatinine.

Results:

The volunteers’ body weight decreased 1.1% (mean) while they exercised. There were strong correlations between all 4 urinary markers of dehydration (r = .73–.84, p < .001). Researchers constructed a composite dehydration index graded from 1 to 6 based on these markers. This index changed from 2.70 before exercising to 3.55 after exercising, which corresponded to dehydration of 1.0% as given by a preliminary reference curve based on 7 previous studies in athletes. Men were slightly dehydrated at baseline (mean: 1.9%) compared with women (mean: 0.7%; p < .001), though age had no influence on the results. A final reference curve that considered both the present results and the 7 previous studies was constructed in which exercise-induced weight loss (x) was predicted by the exponential equation x = 0.20 dehydration index1.86.

Conclusion:

Urine sampling can be used to estimate weight loss due to dehydration in adults up to age 70. A robust dehydration index based on four indicators reduces the influence of confounders.

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Robert A. Oppliger, Scott A. Magnes, LeRoy A. Popowski and Carl V. Gisolfi

To reduce the adverse consequences of exertion-related and acute intentional dehydration research has focused on monitoring hydration status. This investigation: 1) compared sensitivity of urine specific gravity (Usg), urine osmolality (Uosm) and a criterion measurement of hydration, plasma osmolality (Posm), at progressive stages of acute hypertonic dehydration and 2) using a medical decision model, determined whether Usg or Uosm accurately reflected hydra-tion status compared to Posm among 51 subjects tested throughout the day. Incremental changes in Posm were observed as subjects dehydrated by 5% of body weight and rehydrated while Usg and Uosm showed delayed dehydration-related changes. Using the medical decision model, sensitivity and specificity were not significant at selected cut-offs for Usg and Uosm. At the most accurate cut-off values, 1.015 and 1.020 for Usg and 700 mosm/kg and 800 mosm/kg for Uosm, only 65% of the athletes were correctly classified using Usg and 63% using Uosm. Posm, Usg, and Uosm appear sensitive to incremental changes in acute hypertonic dehydration, however, the misclassified outcomes for Usg and Uosm raise concerns. Research focused on elucidating the factors affecting accurate assessment of hydration status appears warranted.

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David S. Rowlands, Darrell L. Bonetti and Will G. Hopkins

Isotonic sports drinks are often consumed to offset the effects of dehydration and improve endurance performance, but hypotonic drinks may be more advantageous. The purpose of the study was to compare absorption and effects on performance of a commercially available hypotonic sports drink (Mizone Rapid: 3.9% carbohydrate [CHO], 218 mOsmol/kg) with those of an isotonic drink (PowerAde: 7.6% CHO, 281 mOsmol/kg), a hypertonic drink (Gatorade: 6% CHO, 327 mOsmol/kg), and a noncaloric placebo (8 mOsmol/kg). In a crossover, 11 cyclists consumed each drink on separate days at 250 ml/15 min during a 2-hr preload ride at 55% peak power followed by an incremental test to exhaustion. Small to moderate increases in deuterium oxide enrichment in the preload were observed with Mizone Rapid relative to PowerAde, Gatorade, and placebo (differences of 88, 45, and 42 parts per million, respectively; 90% confidence limits ±28). Serum osmolality was moderately lower with Mizone Rapid than with PowerAde and Gatorade (–1.9, –2.4; mOsmol/L; ±1.2 mOsmol/L) but not clearly different vs. placebo. Plasma volume reduction was small to moderate with Mizone Rapid, PowerAde, and Gatorade relative to placebo (–1.9%, –2.5%, –2.9%; ± 2.5%). Gut comfort was highest with Mizone Rapid but clearly different (8.4% ± 4.8%) only vs PowerAde. Peak power was highest with Mizone Rapid (380 W) vs. placebo and other drinks (1.2–3.0%; 99% confidence limits ±4.7%), but differences were inconclusive with reference to the smallest important effect (~1.2%). The outcomes are consistent with fastest fluid absorption with the hypotonic sports drink. Further research should determine whether the effect has a meaningful impact on performance.