Fluent Essays

Read these three articles then write a single paragraph synopsis for each articles. effect_of_exercise_induced_dehydration_on_endurance_performance.pdf does_dehydration_impair_exercise_performance.pdf dehydration_and_endurance_performance_in_competitive_athletes.pdf Unformatted Attachment Preview Downloaded from bjsm.bmj.com on October 31, 2012 - Published by group.bmj.com BJSM Online First, published on July 4, 2012 as 10.1136/bjsports-2012-090958 Review Effect of exercise-induced dehydration on endurance performance: evaluating the impact of exercise protocols on outcomes using a meta-analytic procedure Eric D B Goulet ▶ Additional materials are published online only. To view these files please visit the journal online (http://bjsm.bmj. com/content/early/recent) Correspondence to Dr. Eric D.B. Goulet, Research Centre on Aging/Faculty of Physical Education and Sports, University of Sherbrooke, 1036 Belvédère Sud, Sherbrooke, Québec, Canada, J1H 4C4; eric.goulet@usherbrooke.ca Received 12 January 2012 Accepted 9 May 2012 ABSTRACT Objective It is purported that exercise-induced dehydration (EID), especially if ≥ 2\% bodyweight, impairs endurance performance (EP). Field research shows that athletes can achieve outstanding EP while dehydrated > 2\% bodyweight. Using the meta-analytic procedure, this study compared the findings of laboratory-based studies that examined the impact of EID upon EP using either ecologically valid (EV) (time-trial exercise) or non-ecologically valid (NEV) (clamped-intensity exercise) exercise protocols. Methods EP outcomes were put on the same scale and represent \% changes in power output between euhydrated and dehydrated exercise tests. Randomeffects model meta-regressions and weighted mean effect summaries, mixed-effects model analogue to the ANOVAs and magnitude-based effect statistics were used to delineate treatment effects. Main results Fifteen research articles were included, producing 28 effect estimates, representing 122 subjects. Compared with euhydration, EID increased (0.09±2.60\%, (p=0.9)) EP under time-trial exercise conditions, whereas it reduced it (1.91±1.53\%, (p<0.05)) with NEV exercise protocols. Only with NEV exercise protocols did EID ≥ 2\% bodyweight impair EP (p=0.03). Conclusions Evidence indicates that (1) EID ≤ 4\% bodyweight is very unlikely to impair EP under real-world exercise conditions (time-trial type exercise) and; (2) under situations of fixed-exercise intensity, which may have some relevance for military and occupational settings, EID ≥ 2\% bodyweight is associated with a reduction in endurance capacity. The 2\% bodyweight loss rule has been established from findings of studies using NEV exercise protocols and does not apply to out-of-doors exercise conditions. Athletes are therefore encouraged to drink according to thirst during exercise. INTRODUCTION Today’s well-accepted notion that exercise-induced dehydration (EID) ≥ 2\% bodyweight impairs endurance performance (EP) has been developed in 2003 by Cheuvront et al1 from the United State Army Research Institute of Environmental Medicine and is endorsed by the American College of Sports Medicine,2 the International Olympic Committee, 3 the American Dietetic Association4 and the Dietitians of Canada.4 Cheuvront et al’s1 conclusion has been reached using the traditional narrative review method with a vote counting procedure, a scientifically invalid method to determine Copyright Article author (or their employer) Goulet EDB. Br J Sports Med (2012). doi:10.1136/bjsports-2012-090958 intervention effect. 5 Moreover, the narrative review has no rigorous mechanism to determine whether a treatment effect is consistent across studies.6 The recommendation to limit dehydration to 2\% bodyweight during exercise is based from results of studies that used exercise protocols where athletes were forced to exercise at fi xed-work rates until exhaustion or at least during part of the exercise protocols.7 These research designs have a poor reliability8 or possess a very low ecological validity,9 thereby suggesting that they should not be used in the establishment of fluid intake guidelines, especially those designed for athletes. In fact, several studies have shown that athletes’ exercise intensity during racing conditions never remains constant but rather constantly varies throughout either on a macro- or micro-scale.10–13 There is no sporting event where athletes are required to exercise until exhaustion. Finally, optimal endurance performance can only be achieved when the knowledge of the distance or time to be completed during an exercise bout is known.14 Using a meta-analytic approach, Goulet 7 has recently demonstrated that EID of up to 4\% bodyweight improves, albeit non-significantly, EP during cycling time-trial type exercise. Moreover, this study demonstrated that drinking to thirst significantly improves EP, compared with drinking below thirst sensation. Interestingly, drinking ahead of thirst did not provide any significant performance advantage, compared with drinking to the dictates of thirst. These fi ndings, deriving from laboratory-based studies, are in line with those observed in several field studies demonstrating that EID correlates with superior EP in marathon runners,15 ultra-marathon runners16 and long-distance triathletes.17 Since Goulet’s7 fi ndings derive from ecologically valid exercise protocols, they therefore represent the best available evidence yet regarding the impact of EID upon EP. Whether or not the 2\% bodyweight loss rule is real or an artefact has never been tested using rigorous statistical procedures. Moreover, unlike that observed during time-trial exercise conditions, the magnitude of the effect of EID during non-ecologically valid (NEV) exercise protocols (clamped-intensity conditions) has never been established. Finally, there is a need to resolve the question of whether or not the impact of EID upon EP differs between ecologically valid (EV) (timetrial exercise) and NEV exercise protocols. 2012. Produced by BMJ Publishing Group Ltd under licence. 1 of 8 Downloaded from bjsm.bmj.com on October 31, 2012 - Published by group.bmj.com Review Using a meta-analytical approach, this study determined and contrasted the magnitude of the effect of EID upon EP for studies that used EV and NEV exercise protocols. Findings clearly highlight that only under NEV exercise scenarios does EID impair EP. METHODS Search strategy A thorough search of the literature using the PubMed and SPORTDiscus databases was performed. The MeSH headings used, alone or in combination, were: ‘dehydration and exercise’, ‘dehydration and endurance performance’, ‘dehydration and exercise performance’, ‘dehydration and exercise-endurance capacity’, ‘hypohydration and exercise’, ‘hypohydration and endurance performance’, ‘hypohydration and exercise performance’, ‘hypohydration and exercise-endurance capacity’, ‘hydration and exercise capacity’, ‘hydration and endurance performance’, ‘exercise-induced dehydration and endurance performance’ or ‘exercise and fluid balance’. The literature search was limited to English language citations. A manual search of the reference section of all articles found during the electronic search was performed. Three key published narrative reviews were manually searched.1 2 18 Case studies, published abstracts, conference proceedings, dissertations or manuscripts published in non-peer reviewed journals were not admissible. The last literature day search was performed on 10 December 2011. Inclusion criteria To be included, studies had to meet all of the following criteria: 1) laboratory-controlled; 2) EID induced during, not before exercise; 3) fluid replacement during exercise given orally; 4) data needed to calculate \% change in power outputs, effect estimates, variances and EID levels reported; 5) if perfect euhydration maintained during exercise (ie, 0\% bodyweight loss): minimum dehydration level set at ≥ 1\% bodyweight loss; 6) if perfect euhydration not achieved during exercise (ie, different from 0\% bodyweight loss): A) euhydration considered when end-of-exercise bodyweight loss within ± 1\% of starting exercise bodyweight; B) minimum EID level set at > 1\% bodyweight loss and; C) difference in EID level between the dehydrated and euhydrated group ≥ 0.45\% bodyweight; 7) same quantity of carbohydrate provided between exercise trials and; 8) EP assessed in compensable exercise-heat stress. Data extraction When necessary, authors were contacted to resolve ambiguities and issues with methodology or fi ndings. Coded variables included: 1) study characteristics; 2) subject physical and fitness characteristics; 3) exercise protocol characteristics; 4) environmental condition characteristics; 5) pre and postexercise bodyweights and; 6) \% changes in power output between experimental conditions. Measurement of exercise duration Exercise duration represents the mean total exercise time (min) completed in the euhydrated and dehydrated group. Measurement of exercise intensity Exercise intensity represents the mean relative maximal oxygen consumption V·O 2Max, at which the exercise protocols were conducted. A weighted average technique was used to 2 of 8 determine exercise intensity of studies that combined multiple bouts of exercise conducted at different intensities.19–24 Measurement of dehydration level Dehydration level is taken as the \% change in bodyweight from pre to postexercise. It is acknowledged that the assessment of EID using changes in bodyweight lacks precision. 25 However, under field conditions, it is the most practical and reliable method that can be used to estimate EID level. Measurement of endurance performance Time-trial type exercise protocol Eighteen studies19 26–31 used time-trials to test EP, with all reporting mean maintained power output. Hence, in these studies, the \% changes in EP were measured using the following formula: \% change in power output Dehydrated group mean power output – euhydrated group mean power output/euhydrated group mean power output ×100. Fixed-power output and incremental to exhaustion type of test Seven studies used fi xed-power output tests to exhaustion,20 22 24 32–34 whereas 3 utilised incremental tests to exhaustion 21 23 to evaluate the impact of EID on EP. With respect to the study of Edwards et al,21 the accumulated number of meters ran during the YO-YO tests (running test to exhaustion) was converted to a running time to exhaustion. In this particular study, it was estimated that subjects started the incremental test to exhaustion at 89\% V·O2Max.35 For the study of Van Schuylenbergh et al,23 the change in peak power output was used to measure EP, which yields similar result to when using time to exhaustion. A negative \% change in power output represents a negative effect of EID on EP, whereas a positive \% change in power output represents a positive effect of EID on EP. According to Hopkins, 36 a 1\% change in power output equals a change of: (1) 1\% in running time-trial speed or time and; (2) 0.4\% in road cycling time-trial time. The \% changes in power output were calculated using the following formulas:37 (1) Fixed-power output to exhaustion test: mean dehydrated group time to exhaustion – mean euhydrated group time to exhaustion/mean euhydrated group time to exhaustion ×100/(\% V·O2Max, at which the test was performed/6.4). (2) Incremental to exhaustion test: mean dehydrated group time to exhaustion – mean euhydrated group time to exhaustion/mean euhydrated group time to exhaustion ×100 (1- (\% V·O2Max, or peak power output at which the test started/100)). STATISTICAL ANALYSES Statistical analyses were performed with SPSS version 12.0.0. (Chicago, Illinois, USA), SPSS macros found in38 and with Comprehensive Meta-Analysis (CMA) version 2.2.048. (Englewood, NewJersey, USA). Unless otherwise noted, all data are reported as mean ± SD with statistical significance set at p≤0.05. The weight of each study consisted of the inverse variance for the net \% change in power output.6 Variance was directly calculated from the reported Δ SE or SD of the net \% change in power output. Missing variances were calculated from exact p values, or when not exactly reported, from p values equal to X, where X is any p value ≤0.05.39 When only p>0.05 was reported, individual variances for net \% changes in power output were estimated as recommended by Higgins and Green.40 CI not including 0 was considered statistically significant. Goulet EDB. Br J Sports Med (2012). doi:10.1136/bjsports-2012-090958 Downloaded from bjsm.bmj.com on October 31, 2012 - Published by group.bmj.com Review Weighted mean effect summary Description of subjects Weighted mean effect summary for EV and NEV exercise protocols was measured using random-effects model. For research articles that included more than one \% change in power output, each outcome was treated independently. However, a separate statistical analysis was performed with only one effect estimate and weighting factor per research article to determine whether it would change outcomes. For EV research protocols, 26–29 31 the qualitative interpretation of the effect of EID on EP under real-world conditions was determined using the spreadsheet developed by Hopkins et al.41 As those studies exclusively used cycling time-trials, the smallest worthwhile \% change in power output was determined for cycling and set at 1.6\% based on an average typical variation in competition time of 1.3\%.42 The smallest worthwhile \% change in power output was obtained by multiplying the variation in cycling competition time by 0.5,43 and then by transforming the threshold competition time to a threshold for cycling power output. 37 A total of 122 subjects were represented in the 15 research manuscripts included in the current analysis. Mean sample size was 8.1±1.8 subjects, with men and women representing 91\% and 9\% of all subjects, respectively. Mean age, weight, height (N=27 studies) and relative V·O2peak , (N=26 studies) of subjects was 25±3 years, 72±4 kg, 178±4 cm and 64±9 ml ⋅ kg-1 ⋅ min−1, respectively. There were no significant differences between EV and NEV exercise protocols for any of the aforementioned variables. Meta-regression and subgroup analysis To determine the influence of moderating variables on the \% changes in EP, mixed-effects analogue to the ANOVAS and random-effects meta-regressions were performed using a priori identified variables. Evaluation of heterogeneity and publication bias Between-study heterogeneity was assessed using the I 2 statistic44 and the Cochran Q test, with p≤0.01 indicating significance.6 Publication bias was explored using funnel plot visual inspection and statistically tested with the Begg test, the Egger test and the classical fail and safe procedure.6 Exercise and endurance performance protocol characteristics Non-ecologically valid exercise protocols Three studies used a continuous, fi xed-power output test to exhaustion conducted at the same relative exercise intensity throughout.32–34 A continuous exercise protocol where a fi rst fi xed-power output bout of exercise was followed by another one of higher intensity to evaluate the effect of EID upon EP was used by 4 studies.20 22 24 Five studies19 30 used a continuous exercise protocol where a fi rst fi xed-power output exercise period was followed by a second one where subjects performed the greatest amount of work possible in a given amount of time to determine the effect of EID on EP. Edwards et al21 used a discontinuous exercise protocol consisting of 1) a 45-min period of cycling at 90\% ventilatory threshold; 2) a 45-min outdoor soccer game and; 3) a YO-YO test to evaluate the impact of the accumulated EID level upon EP. Van Schuylenbergh et al23 used a discontinuous exercise protocol consisting of 1) a 20-min warm-up period; 2) an ~ 25-min long incremental test to exhaustion; 3) a 5-min recovery period; 4) a 120-min long exercise period; 4) a 5-min recovery period and; 5) an ~ 25-min long incremental test to exhaustion to measure the impact of EID upon EP. Among the aforementioned studies, all used cycling exercise, with the exception of Fallowfield et al, 32 who used running exercise and Edwards et al21 who combined cycling and running exercises. Ecologically valid exercise protocols RESULTS Search result manuscripts19–24 26–34 45–48 A total of 19 were fi rst identified. Of these, 15 met the inclusion criteria.19–24 26–34 The investigation of Daries et al46 was excluded because a different amount of carbohydrate was administered between exercise trials, those of Barr et al45 and Mudambo et al48 because they were not specifically designed to measure EP and that of Fritzsche et al47 because it measured the effect of EID on maximal cycling power output, not EP. Among the included research manuscripts, two individual studies were performed in Edwards et al, 21 McConell et al, 22 Below et al19 and Kay and Marino29 and 3,4 and 5 in McConnel et al, 30 Backx et al27 and Dugas et al, 28 respectively. Thus, the research yielded a total of 28 studies. Among those, 13 used EV exercise protocols, 26–29 31 whereas 15 used NEV exercise protocols.19–24 30 32–34 A concise description of each study is presented in table 1. Thirteen studies resorted to the use of cycling time-trial type exercise protocol to measure the effect of EID on EP. Dugas et al28 used an 80 km time-trial, whereas the remaining studies26 27 29 31 utilised a time-trial protocol where subjects had to cover the greatest possible distance in 60 min. The latter racing format is often used during ultra-marathon races and cycling criteriums. The most prestigious cycling record to hold, the hour-record, is the best example of such a racing format. Environmental conditions, exercise intensity and exercise duration The mean ambient temperature, relative humidity, exercise intensity and exercise duration observed during NEV exercise protocols was 24±4°C, 46±10\%, 74±5\% of V·O2Max, and 91±34 min, respectively, whereas during EV exercise protocols it was 26±7°C, 61±9\%, 68±14\% of V·O2peak , and 86±34 min, respectively. With the exception of relative humidity (p=0.001), there were no significant differences in any parameter between research designs. Characteristics of the included research investigations The 28 studies were published between 1989 and 2009, from 10 different peer-reviewed journals. One research investigation was published in the 1980s, 34 seven between the years 1990 and 199919 22 24 30–33 and seven between the years 2000 and 2009. 20 21 23 26–29 Four research investigations were performed in the United Kingdom, 27 32–34 four in Australia, 20 22 29 30 three in South Africa, 24 28 31 two in the USA,19 26 one in New Zealand21 and one in Belgium.23 Goulet EDB. Br J Sports Med (2012). doi:10.1136/bjsports-2012-090958 Dehydration level For NEV exercise protocols, the mean EID level of the dehydrated group was 2.14±0.62\% bodyweight, whereas that of the euhydrated group was 0.48±0.32\% bodyweight, for a mean difference in hydration level between groups of 1.65±0.64\% (95\% CI: 1.30 to 2.00\%) bodyweight. Eight studies were completed with an EID level < 2\% bodyweight, whereas 7 were terminated with an EID level ≥ 2\% bodyweight. For EV 3 of 8 Downloaded from bjsm.bmj.com on October 31, 2012 - Published by group.bmj.com Review Table 1 References (alphabetical order) Number of subject, gender and age Ecologically valid exercise protocols 10 recreationally-trained subBachle et al26 jects, 4 men, 6 women, 29±6 years 8 trained cyclists, 8 men, 0 Backx et al27 woman, 29 ± 7 years Exercise protocol Ambient Relative temperature (°C) humidity (\%) Dehydration level (\% bodyweight) 1-h self-paced laboratory-based cycling time-trial 21°C 72\% Dehydrated group: −1.02\% Euhydrated group: +0.8\% 1-h self-paced laboratory-based cycling time-trial 20°C 70\% A. LF trial: −1.7\%; FAM trial: −0.9\% B. MF trial: −1.3\%; HF trial: −0.7\% C. LF trial: −1.7\%; HF trial: −0.7\% D. MF tri ... Purchase answer to see full attachment