Samuel Mettler

Statement of the Second International Exercise-Associated Hyponatremia Consensus Development Conference, New Zealand, 2007.

Tamara Hew-Butler, DPM, PhD,* J. Carlos Ayus, MD,† Courtney Kipps, BMBS, MSc,‡ Ronald J. Maughan, PhD,§ Samuel Mettler, MSc,¶ Willem H. Meeuwisse, MD, PhD (chair),k Anthony J. Page, MBChB, MD,** Stephen A. Reid, MBBS, PhD,†† Nancy J. Rehrer, PhD,‡‡ William O. Roberts, MD, MSc,§§ Ian R. Rogers, MBBS,¶¶ Mitchell H. Rosner, MD,kk Arthur J. Siegel, MD,*** Dale B. Speedy, MBChB, MD,††† Kristin J. Stuempfle, PhD,‡‡‡ Joseph G. Verbalis, MD,§§§ Louise B. Weschler, MAT, PT,¶¶¶ and Paul Wharam, MMedSckkk

Hyponatremia among runners in the Zurich Marathon.

Objective:Hyperhydration and exercise-associated hyponatremia (EAH) are critical issues during endurance events. We studied a cohort of marathon runners to examine EAHs prevalence in a marathon with a short time limit and to investigate underlying mechanisms that may be responsible for its development. Design:Observational cohort study. Setting:2006 Zurich Marathon (cool and rainy weather, time limit of 5 hours). Participants:167 marathon runners were recruited the month before the race. Main Outcome Measures:Body mass, plasma sodium, and osmolality were measured just before the start and immediately after the race. Fluid intake during the race was ascertained by a recall questionnaire. Results:Five subjects (3 %) developed asymptomatic EAH, and no symptomatic EAH was found. Body mass change during the race correlated similarly with postrace sodium levels (r = −0.72, P < 0.0001) and with sodium change during the race (r = −0.66, P < 0.0001). Postrace sodium levels correlated significantly with sodium change during the race (r = 0.74, P < 0.0001). Fluid intake correlated significantly (r = −0.43, P < 0.0001) with plasma sodium change between the start and finish of the race. Postrace sodium levels and postrace osmolality were significantly correlated (r = 0.68, P < 0.0001). Conclusion:In this study we observed a relatively low incidence of EAH in subjects running the marathon in around 2.5 to 5 hours and in a cool environment. Plasma sodium change during the race and postrace sodium levels correlated with body mass change. There was also a direct correlation between fluid intake and plasma sodium change during the race.

Effects of 3-week consumption of green tea extracts on whole-body metabolism during cycling exercise in endurance-trained men.

The consumption of green tea has been generally associated with beneficial effects on human whole-body metabolism and recent investigations with animals indicate favorable effects of green tea extracts (GTE) on energy metabolism during exercise and aerobic exercise performance. Therefore, the purpose of this study was to examine the effects of a three-week supplementation with GTE on human energy metabolism during submaximal cycling exercise. In a randomized, double-blind crossover setting, ten healthy endurance-trained men exercised for 2 hours at 50 % W(max) before and after three weeks of placebo or GTE supplementation (GTE containing about 160 mg x day(-1) total catechins, of which about 70 mg x day(-1) was epigallocatechin-3-gallate). The GTE supplementation did not influence indices of fat and energy metabolism (fatty acids, 3-beta-hydroxybutyrate, triacylglycerol, low-density-lipoprotein cholesterol, total cholesterol, lactate, glucose, oxygen uptake, respiratory exchange ratio, energy expenditure), inflammation processes (interleukin-6, C-reactive protein), and oxidative stress (thiobarbituric-acid reactive substances, oxidized low-density-lipoprotein cholesterol), but plasma creatine kinase concentration at rest and during exercise was significantly lower (p = 0.039) and high-density-lipoprotein cholesterol concentration at rest was significantly higher (p = 0.043) compared to placebo. In conclusion, these results suggest only slight effects on whole-body metabolism after supplementation with GTE.

No Effects of Three-week Consumption of a Green Tea Extract on Time Trial Performance in Endurance-trained Men

The purpose of this study was to examine the effects of three-week consumption of green tea extract (GTE) supplementation on time trial performance and metabolism during cycling in endurance athletes. Nine endurance-trained men participated in this double-blind and placebo-controlled cross-over study. At the end of the supplementation period with GTE (159 mg/day total catechins) or placebo, respectively, subjects cycled at 50 % of the individual maximal power output for 2 hours, followed by a 30-minute time trial. Respiratory gas exchange, fatty acids, 3-beta-hydroxybutyrate, lactate, glucose, interleukin-6, thiobarbituric acid reactive substances, creatine kinase, and C-reactive protein (CRP) were measured 1 hour before, during, and 1 hour after the exercise test. Blood lipids were measured at rest before cycling. There was no significant effect on performance, energy metabolism, or any other measured parameter, except for CRP, which was significantly reduced (p = 0.045) after GTE supplementation compared to placebo. GTE supplementation did not affect time trial performance and energy metabolism in endurance-trained men in the non-fasting state. Further studies with athletes, particularly in the fed state, but with higher GTE doses, are needed to address the question whether green tea may influence energy metabolism and performance in athletes.

Additive postprandial blood glucose-attenuating and satiety-enhancing effect of cinnamon and acetic acid.

Cinnamon and vinegar or acetic acid were reported to reduce the postprandial blood glucose response. We hypothesized that the combination of these substances might result in an additive effect. Therefore, we determined the 2-hour postprandial blood glucose and satiety response to a milk rice meal supplemented with either cinnamon or acetic acid on their own or in combination. Subjects (n = 27) consumed the meal on 4 occasions as either pure (control trial), with 4 g cinnamon, 28 mmol acetic acid, or the combination of cinnamon + acetic acid. Blood glucose and satiety were assessed before eating and 15, 30, 45, 60, 90, and 120 minutes postprandially. At 15 minutes, the combination of cinnamon + acetic acid resulted in a significantly reduced blood glucose concentration compared with the control meal (P = .021). The incremental area under the blood glucose response curve over 120 minutes did, however, not differ between the trials (P = .539). The satiety score of the cinnamon + acetic acid trial was significantly higher than that in the control trial at 15 (P = .024) and 30 minutes (P = .024), but the incremental area under the curve of the satiety response did not differ (P = .116) between the trials. In conclusion, the significant effect of the combination of cinnamon and acetic acid on blood glucose and satiety immediately after meal intake indicated an additive effect of the 2 substances. Whether larger doses of cinnamon and acetic acid may result in a more substantial additive effect on blood glucose or satiety remains to be investigated.

Is beetroot juice more effective than sodium nitrate? The effects of equimolar nitrate dosages of nitrate-rich beetroot juice and sodium nitrate on oxygen consumption during exercise

Dietary nitrate has been reported to lower oxygen consumption in moderate- and severe-intensity exercise. To date, it is unproven that sodium nitrate (NaNO3(-); NIT) and nitrate-rich beetroot juice (BR) have the same effects on oxygen consumption, blood pressure, and plasma nitrate and nitrite concentrations or not. The aim of this study was to compare the effects of different dosages of NIT and BR on oxygen consumption in male athletes. Twelve healthy, well-trained men (median [minimum; maximum]; peak oxygen consumption: 59.4 mL·min(-1)·kg(-1) [40.5; 67.0]) performed 7 trials on different days, ingesting different nitrate dosages and placebo (PLC). Dosages were 3, 6, and 12 mmol nitrate as concentrated BR or NIT dissolved in plain water. Plasma nitrate and nitrite concentrations were measured before, 3 h after ingestion, and postexercise. Participants cycled for 5 min at moderate intensity and further 8 min at severe intensity. End-exercise oxygen consumption at moderate intensity was not significantly different between the 7 trials (p = 0.08). At severe-intensity exercise, end-exercise oxygen consumption was ~4% lower in the 6-mmol BR trial compared with the 6-mmol NIT (p = 0.003) trial as well as compared with PLC (p = 0.010). Plasma nitrite and nitrate concentrations were significantly increased after the ingestion of BR and NIT with the highest concentrations in the 12-mmol trials. Plasma nitrite concentration between NIT and BR did not significantly differ in the 6-mmol (p = 0.27) and in the 12-mmol (p = 0.75) trials. In conclusion, BR might reduce oxygen consumption to a greater extent compared with NIT.

Carbohydrates and exercise performance in non-fasted athletes: A systematic review of studies mimicking real-life

There is a consensus claiming an ergogenic effect of carbohydrates ingested in the proximity of or during a performance bout. However, in performance studies, the protocols that are used are often highly standardized (e.g. fasted subjects, constant exercise intensity with time-to-exhaustion tests), and do not necessarily reflect competitive real-life situations. Therefore, we aimed at systematically summarizing all studies with a setting mimicking the situation of a real-life competition (e.g., subjects exercising in the postprandial state and with time-trial-like performance tests such as fixed distance or fixed time tests). We performed a PubMed search by using a selection of search terms covering inclusion criteria for sport, athletes, carbohydrates, and fluids, and exclusion criteria for diseases and animals. This search yielded 16,658 articles and the abstract of 16,508 articles contained sufficient information to identify the study as non-eligible for this review. The screening of the full text of the remaining 150 articles yielded 17 articles that were included in this review. These articles described 22 carbohydrate interventions covering test durations from 26 to 241 min (mostly cycling). We observed no performance improvement with half of the carbohydrate interventions, while the other half of the interventions had significant improvement between 1% and 13% (improvement with one of five interventions lasting up to 68 min and with 10 of 17 interventions lasting between 70 and 241 min). Thus, when considering only studies with a setting mimicking real-life competition, there is a mixed general picture about the ergogenic effect of carbohydrates ingested in the proximity of or during a performance bout with an unlikely effect with bouts up to perhaps 70 min and a possible but not compelling ergogenic effect with performance durations longer than about 70 min.

Influence of Training Status on Glycemic Index

The glycemic index (GI) represents the relative postprandial blood glucose response to the ingestion of a food containing carbohydrate. Although regular physical exercise may influence glucose metabolism, it is not yet known if chronically performed exercise also affects the GI. The objective of this study was, therefore, to determine the GI of common meals (three breakfast cereals: B, C, D) in healthy, nonsmoking young males 2 who were either endurance-trained (n = 12) or sedentary (n = 11). Glucose was used as the reference food. The GI value between the endurance-trained and sedentary subjects differed significantly (p < 0.01). Pair-wise comparisons between endurance-trained and sedentary subjects within the different test meals were significant for test meal D (p = 0.002), marginally non-significant for meal C (p = 0.052) and not significant for meal B (p = 0.204). These results suggest that the GI of some complex foods may depend on the training status of healthy young subjects.

Regular Endurance Training Does Not Influence the Glycemic Index Determination in Women

Objective: This study investigated the influence of regular endurance training on the glycemic index (GI) of a breakfast cereal in women as previous results from men indicate that endurance training may influence the GI. Methods: Subjects were 17 sedentary (SE) and 19 endurance trained (ET) healthy, young, adult women of normal body mass index. All subjects performed two tests with the reference food glucose and two tests with a breakfast cereal in a randomized order. Capillary and venous whole blood glucose as well as venous plasma insulin was measured. Results: The GI did not differ between SE and ET, irrespective of its calculation from the capillary (mean ± standard error: 61.4 ± 4.3 and 69.5 ± 4.7 for SE and ET respectively, p = 0.21) or the venous blood glucose (60.8 ± 8.1 and 64.4 ± 6.2, p = 0.72). The insulinemic index did not differ between the SE and ET subjects (p = 0.75). Conclusion: The results come along with many other data, indicating that the GI seems to be independent of subject-specific factors, but are in contrast to previous results obtained with men where we found a GI dependence on the training state.

Influence of Caffeine and Sodium Citrate Ingestion on 1,500-m Exercise Performance in Elite Wheelchair Athletes: A Pilot Study

The aim of this study was to investigate whether caffeine and/or sodium citrate have an ergogenic effect on the 1,500-m exercise performance in elite wheelchair athletes. A placebo-controlled, randomized, cross-over and double-blind study design was conducted with the four treatments placebo, caffeine, sodium citrate and the combination of caffeine and sodium citrate. Nine healthy, elite wheelchair-racing athletes (median: [min; max] age: 28 y [23; 54]; height: 173 cm [165; 188]; weight: 62.9 kg [48.9; 68.4], category T53/54) completed the study. All athletes were national team members, including several Paralympic Games, World and European Championship medalists. The athletes performed a 1,500-m time trial four times on a wheelchair training roller. Time to complete 1,500-m, pH, bicarbonate and sodium concentration as well as lactate concentration were measured. The time to complete 1,500-m was not significantly different between the four treatments (placebo: 170.6 s [141.7; 232.0]; caffeine: 179.5 s [134.8; 239.6]; sodium citrate: 178.3 s [136.4; 247.1]; combination: 177.6 s [136.1; 256.2]). However, pH and bicarbonate concentrations were significantly increased with sodium citrate ingestion compared with placebo. Moreover, maximal lactate concentrations were significantly higher in the caffeine and the combination treatment compared with placebo. The supplementation with sodium citrate and/or caffeine did not provide an ergogenic effect on the 1,500-m exercise performance in wheelchair elite athletes.