Nancy J. Rehrer

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

Time – motion analysis of professional rugby union players during match-play

Abstract The aim of this study was to quantify the movement patterns of various playing positions during professional rugby union match-play, such that the relative importance of aerobic and anaerobic energy pathways to performance could be estimated. Video analysis was conducted of individual players (n=29) from the Otago Highlanders during six “Super 12” representative fixtures. Each movement was coded as one of six speeds of locomotion (standing still, walking, jogging, cruising, sprinting, and utility), three states of non-running intensive exertion (rucking/mauling, tackling, and scrummaging), and three discrete activities (kicking, jumping, passing). The results indicated significant demands on all energy systems in all playing positions, yet implied a greater reliance on anaerobic glycolytic metabolism in forwards, due primarily to their regular involvement in non-running intense activities such as rucking, mauling, scrummaging, and tackling. Positional group comparisons indicated that while the greatest differences existed between forwards and backs, each positional group had its own unique demands. Front row forwards were mostly involved in activities involving gaining/retaining possession, back row forwards tended to play more of a pseudo back-line role, performing less rucking/mauling than front row forwards, yet being more involved in aspects of broken play such as sprinting and tackling. While outside backs tended to specialize in the running aspects of play, inside backs tended to show greater involvement in confrontational aspects of play such as rucking/mauling and tackling. These results suggest that rugby training and fitness testing should be tailored specifically to positional groups rather than simply differentiating between forwards and backs.

Breaking prolonged sitting reduces postprandial glycemia in healthy, normal-weight adults: a randomized crossover trial

BACKGROUND Sedentary behavior is a risk factor for cardiometabolic disease. Regularly interrupting sedentary behavior with activity breaks may lower this risk. OBJECTIVE We compared the effects of prolonged sitting, continuous physical activity combined with prolonged sitting, and regular activity breaks on postprandial metabolism. DESIGN Seventy adults participated in a randomized crossover study. The prolonged sitting intervention involved sitting for 9 h, the physical activity intervention involved walking for 30 min and then sitting, and the regular-activity-break intervention involved walking for 1 min 40 s every 30 min. Participants consumed a meal-replacement beverage at 60, 240, and 420 min. RESULTS The plasma incremental area under the curve (iAUC) for insulin differed between interventions (overall P < 0.001). Regular activity breaks lowered values by 866.7 IU · L(-1) · 9 h(-1) (95% CI: 506.0, 1227.5 IU · L(-1) · 9 h(-1); P < 0.001) when compared with prolonged sitting and by 542.0 IU · L(-1) · 9 h(-1) (95% CI: 179.9, 904.2 IU · L(-1) · 9 h(-1); P = 0.003) when compared with physical activity. Plasma glucose iAUC also differed between interventions (overall P < 0.001). Regular activity breaks lowered values by 18.9 mmol · L(-1) · 9 h(-1) (95% CI: 10.0, 28.0 mmol · L(-1) · 9 h(-1); P < 0.001) when compared with prolonged sitting and by 17.4 mmol · L(-1) · 9 h(-1) (95% CI: 8.4, 26.3 mmol · L(-1) · 9 h(-1); P < 0.001) when compared with physical activity. Plasma triglyceride iAUC differed between interventions (overall P = 0.023). Physical activity lowered values by 6.3 mmol · L(-1) · 9 h(-1) (95% CI: 1.8, 10.7 mmol · L(-1) · 9 h(-1); P = 0.006) when compared with regular activity breaks. CONCLUSION Regular activity breaks were more effective than continuous physical activity at decreasing postprandial glycemia and insulinemia in healthy, normal-weight adults. This trial was registered with the Australian New Zealand Clinical Trials registry as ACTRN12610000953033.

Fluid and Electrolyte Balance in Ultra-Endurance Sport

AbstractIt is well known that fluid and electrolyte balance are critical to optimal exercise performance and, moreover, health maintenance. Most research conducted on extreme sporting endeavour (>3 hours) is based on case studies and studies involving small numbers of individuals. Ultra-endurance sportsmen and women typically do not meet their fluid needs during exercise. However, successful athletes exercising over several consecutive days come close to meeting fluid needs. It is important to try to account for all factors influencing bodyweight changes, in addition to fluid loss, and all sources of water input. Increasing ambient temperature and humidity can increase the rate of sweating by up to approximately 1 L/h. Depending on individual variation, exercise type and particularly intensity, sweat rates can vary from extremely low values to more than 3 L/h.Over-hydration, although not frequently observed, can also present problems, as can inappropriate fluid composition. Over-hydrating or meeting fluid needs during very long-lasting exercise in the heat with low or negligible sodium intake can result in reduced performance and, not infrequently, hyponatraemia. Thus, with large rates of fluid ingestion, even measured just to meet fluid needs, sodium intake is vital and an increased beverage concentration [30 to 50 mmol/L (1.7 to 2.9g NaCl/L) may be beneficial. If insufficient fluids are taken during exercise, sodium is necessary in the recovery period to reduce the urinary output and increase the rate of restoration of fluid balance.Carbohydrate inclusion in a beverage can affect the net rate of water assimilation and is also important to supplement endogenous reserves as a substrate for exercising muscles during ultra-endurance activity. To enhance water absorption, glucose and/or glucose-containing carbohydrates (e.g. sucrose, maltose) at concentrations of 3 to 5% weight/volume are recommended. Carbohydrate concentrations above this may be advantageous in terms of glucose oxidation and maintaining exercise intensity, but will be of no added advantage and, if hyperosmotic, will actually reduce the net rate of water absorption.The rate of fluid loss may exceed the capacity of the gastrointestinal tract to assimilate fluids. Gastric emptying, in particular, may be below the rate of fluid loss, and therefore, individual tolerance may dictate the maximum rate of fluid intake. There is large individual variation in gastric emptying rate and tolerance to larger volumes. Training to drink during exercise is recommended and may enhance tolerance.

THE IMPORTANCE OF VOLUME IN REGULATING GASTRIC EMPTYING

There is now substantive evidence that the provision of exogenous carbohydrate at high rates (1-2 g. min-1) can enhance performance during prolonged exercise. This finding has revived research into the factors determining the rate of exogenous carbohydrate delivery during exercise. While the rate of muscle oxidation of exogenous carbohydrate could be determined by the rate of gastric emptying or of intestinal carbohydrate absorption or of muscle glucose uptake and oxidation, most physiologists seem to have assumed that gastric emptying is the factor that limits the rate of exogenous carbohydrate delivery during exercise. Furthermore, studies of gastric emptying have suggested that the carbohydrate content of the ingested solution is an important factor determining its rate of gastric emptying. However, the findings of recent studies employing a repeated drinking design suggest that the gastric volume and therefore the pattern of drinking during exercise will have a significant, possibly major, influence on the rate of both carbohydrate and water delivery from any solution. This review considers this evidence and its practical implications for athletes who wish to ingest carbohydrate during exercise and for exercise physiologists designing studies to optimize carbohydrate delivery to muscle during exercise. It is proposed that, if gastric volume is an important determinant of the rate of gastric emptying, a more standardized method for reporting the rates of gastric emptying of different solutions should be adopted.

Effects of dehydration on gastric-emptying and gastrointestinal distress while running

Gastrointestinal distress is commonly reported by athletes after ingestion of a beverage. We speculate that ingestion may be occurring after dehydration has taken place. The high prevalence of GI disorders in marathon runners who have lost greater than or equal to 4% body weight supports this theory. To test this theory, the effects of dehydration, and dehydration in combination with endurance running, on gastric emptying (GE) and frequency of gastrointestinal (GI) complaints were tested in this experiment. A complete cross-over study was designed. Sixteen subjects ingested 8 ml.kg BW-1 of a 7% carbohydrate (296 mOsm.kg-1), solution after a euhydration or dehydration regime. Dehydration (4% BW loss) was produced by 60% maximal speed running at 30 degrees C or by intermittent sauna exposure at 100 degrees C. Euhydration experiments were conducted with a 2 h rest period with water administered at 20 and 40 min. Gastric drink volumes were measured every 10 min for 40 min. Emptying curves were compared using semi-log transformation of the percentage emptying data and simple linear regression. The slope of each line was used as a measure of average GE rate. Dehydration-exercise resulted in slower GE than in all other treatments (P less than 0.05). ANOVA revealed significant effects of dehydration (P less than 0.05) and exercise (P less than 0.05), these two effects being additive in delaying GE. GI complaints were reported by 37.5% of the subjects during dehydration-exercise experiments. No GI disturbance was reported in other tests.(ABSTRACT TRUNCATED AT 250 WORDS)

Induction and Decay of Short-Term Heat Acclimation in Moderately and Highly Trained Athletes

A rethinking of current heat-acclimation strategies is required as most research and advice for improving physiological strain in the heat includes maintaining hydration using long-term acclimation protocols (>10 days). Furthermore, these strategies have tended to use untrained and moderately trained participants. Therefore, the aims of this review were to (i) investigate the effectiveness of short-term heat acclimation (STHA) with moderately and highly trained athletes; (ii) determine the importance of fluid regulatory strain, which has a thermally independent role in heat adaptation; (iii) assess the impact of STHA on a marker of thermotolerance (inducible heat-shock protein 70 [HSP70]); and (iv) provide further information on the decay of acclimation to heat. The review suggests that 5-day STHA is effective, and adaptations may be more pronounced after fluid regulatory strain from a dehydration-acclimation regimen. Furthermore, highly trained athletes may have similar physiological gains to those who are less trained using STHA. However, research has tended to focus on untrained or moderately trained participants and more information is required for highly trained populations. HSP70 response is upregulated across STHA. This indicates increased thermotolerance and protective adaptive change that may indicate HSP70 response as a useful marker of heat acclimation. Physiological adaptations after heat acclimation are relatively short term and may vanish only a few days or weeks after removal from heat exposure. From a practical perspective 5-day STHA may be the preferred acclimation regimen for moderately and highly trained athletes as it has been shown to be effective, less expensive and less likely to disrupt the tapering for competition in elite performers. Furthermore, updated information on the time course of acclimation decay may allow a reliable estimate of how long individuals can be free from heat exposure before reacclimation is required. This is particularly pertinent in present times as many athletes, civilians andmilitary personnel increasingly have to relocate to different climates of the world, often within a short period of time.

Physiological changes and gastro-intestinal symptoms as a result of ultra-endurance running

SummaryOne hundred and seventy-two competitors of the Swiss Alpine Marathon, Davos, Switzerland, 1988, volunteered for this research project. of these volunteers 170 (158 men, 12 women) finished the race (99%). The race length was 67 km with an altitude difference of 1,900 m between the highest and lowest points. Mean age was 39 (SEM 0.8) years. Average finishing times were 8 h 18 min (men) and 8 h 56 min (women). Loss of body mass averaged 3.4% body mass [mean 3.3 (SEM 0.2)%; 4.0 (SEM 0.4)%; men and women, respectively]. Blood samples from a subgroup of 89 subjects (6 women and 83 men) were taken prior to and immediately after completion of the race. Changes in haemoglobin (9.3 mmol·l−1 pre-race, 9.7 mmol·l−1 post-race) and packed cell volume (0.44 pre, 0.48 post-race) were in line with the moderate level of dehydration displayed by changes in body mass. Mean plasma volume decreased by 8.3%. No significant changes in plasma osmolality, sodium, or chloride were observed but plasma potassium did increase by 5% (4.2 mmol·l−1 pre-race, 4.4 mmol·l−1 post-race). Mean fluid consumption was 3290 (SEM 103) ml. Forty-three percent of all subjects, and 33% of those who gave blood samples, complained of gastro-intestinal (GI) distress during the race. No direct relationship was found between the quantity or quality of beverage consumed and the prevalence of GI symptoms. The circulating concentration of several GI hormones was measured and several were found to be significantly elevated (P<0.05) after the race [mean values: gastrin 159.6 (SEM 17.8) ng·l−1; vaso-active intestinal peptide 224.3 (SEM 20.1) ng·l−1; peptide histidine isoleucine 311.1 (SEM 27.5) ng·l−1 ; motilin 214.1 (SEM 15.1) ng·l−1] but larger increases were not found to be significantly correlated with GI symptoms. Plasma cortisol, adrenaline, and noradrenaline concentrations were significantly higher after the race compared to resting values (P<0.05). There was a trend for post-race noradrenaline values to be lower in sufferers of GI disturbance. The post-race plasma noradrenaline concentration was significantly lower specifically in those runners with intestinal cramps. Also, the resting plasma cortisol concentration was significantly lower in those individuals who developed intestinal cramps during the race. Plasma creatine phosphokinase, alanine aminotransferase and aspartate aminotransferase activities were increased following the race, which may indicate that there was tissue damage. An increase in plasma potassium concentration was observed after the race in individuals with GI complaints [0.29 (SEM 0.07) mmol·l−1 increase], whereas no increase was observed in individuals without GI symptoms. An inability of the Na+-K+ pump to keep pace with the needs of skeletal muscle (as well in the intestinal tract) may have accounted for the high plasma potassium values immediately following exercise and may have played a role in the development of GI disorders. However, many other sources of K+ release may have accounted for the elevated plasma K+ (skeletal muscle, liver and red blood cells) in such sufferers and the correlation between the increase in K+ and GI symptoms may be an indirect one.

Exercise and training effects on gastric-emptying of carbohydrate beverages

Carbohydrate containing drinks are commonly consumed as an ergogenic aid during endurance sports activities. The efficacy of a given drink is limited by the rate of absorption, which is in turn limited by gastric emptying. A myriad of factors influence gastric emptying. The influence of several of these factors (training status, exercise intensity, and carbohydrate composition) was investigated by repeated experiments using a nasogastric tube and a modification of the technique of George. A group of well-trained bicyclists and a group of untrained subjects performed similar experiments. Three different carbohydrate containing drinks (15 g.100 ml-1 glucose (G), 15 g.100 ml-1 maltodextrin plus 3 g.100 ml-1 fructose (MD), 7 g.100 ml-1 sucrose (I] and artificially sweetened water were compared during rest and 50 and 70% Wmax bicycling. Experimental design was crossover. There was a trend for the carbohydrate drinks to empty initially more slowly under the influence of exercise. Differences in drink volume remaining in the stomach were significant (P less than 0.05), with I at 10 min (70%, mean = 48.9%; rest, mean = 30.5%) and at 20 min (70%, mean = 28.9%; rest, mean = 23.8%) and with MD at 10 min (70%, mean = 71.1%; rest, mean = 55.9%). A similar trend was also seen with 50% Wmax exercise; however, this trend was only significant with MD at 10 min (50%, mean = 72.1%; rest, mean = 55.9%). Drink composition was a much stronger inhibitor of gastric emptying. However, all drinks emptied exponentially with fast-phase initial emptying rates. No differences in gastric emptying or secretion were observed between trained and untrained subjects.

Determination of total gastric volume, gastric secretion and residual meal using the double sampling technique of George.

In literature several techniques are described for the measurement of gastric emptying. One of these is the double sampling technique of George which has the advantage that it enables multiple measurements of total gastric volume in one experiment. In order to estimate net gastric emptying, however, it is important to differentiate between the test meal volume present in the stomach and gastric secretion. In the present study Georges technique was extended with a calculation procedure to estimate gastric secretion and net test meal outflow. An in vitro experiment was carried out which showed an accuracy of 5-10% for this method. An in vivo comparison was made with Hunts chloride technique, which is used for estimating gastric secretion. Sixteen subjects participated in a 60 minute test with water as a test meal. Regression analysis showed a high degree of correlation (R2 = 0.99) between Hunts method and the proposed method. The data obtained indicate that the proposed method gives a reliable estimation of net gastric emptying and is simple to do as no further measurements have to be carried out other than those needed for Georges method.