Hydration and Physical Activity
Recruitment Not mentioned
Design Experimental matched trial, randomized crossover
Blinding used (if applicable) Not mentioned
Intervention (if applicable) L (low Na drink) group vs H (high Na drink) group; different volumes of beverage (4 trials, A-D) consumed after exercise-induced dehydration.
Statistical Analysis
Comparisons made between treatments w/in each group (A-D) and between groups (L vs H) to examine effects of drink composition and volume; Initial 2-way repeated measures ANOVA. If normally-distributed, followed by 1-way ANOVA and Tukey's multiple range test as appropriate. Non-normal followed by Kruskal-Wallis k-sample test and Mann-Whitney test as appropriate. Sig level of p<0.05.
Timing of Measurements: 4 trials, each separated by 1 week
Prior to study: VO2max determined; familiarization w/protocol
Trials: Intermittent exercise to induce 2% body mass loss followed by ingestion of test drink; middle/late PM after 6h fast (excluding water). Rest in moderate temp room (20-25C) for 15 min; blood sample taken; urine collected; showered; body mass obtained. Dehydration initiated by 10 min immersion in 41C water tank; dried and weighed; Exercise in warm, humid environment (30-32C, 70-90%RH); 10 min cycling at 60% VO2max, followed by 5 min rest (body weight taken). Pattern repeated until 2% body mass lost or until completed 10-6 min bouts.
Post-exercise: Cool down; showered; remained in cool environment; body mass taken; 30 min rest, blood samples taken, urine sample collected, as well as at 1, 2, 4, 6h after end of rehydration period; over next 60 min, consumed 1 of rehydration beverages, divided into 4 equal portions, ea of which was consumed over 15 min period
Dependent Variables
- Body mass lost (weight)
- Urine vol and composition (electrolyte levels - flame photometry, Na, K; freezing point depression, Osm; coulometric titration, Cl)
- Blood and plasma volumes (Hgb and Hct used to calculate)
Independent Variables
Vol of drink - varied in relation to sweat loss
| Trial | Volume Ingested |
| A | .5 mass loss |
| B | Equal to mass loss |
| C | 1.5 times mass loss |
| D | 2 times mass loss |
Na-content of drink - Designed to mirror the Na content of the upper and lower ends of Na content of sweat
L - 23 mmol/l-1 Na conc
H - 61 mmol/l-1 Na conc
Control Variables
Exercise and recovery temps; all exercise done at 60% VO2max; Body weight loss of 2%; rate of fluid consumption
Initial N: 12 M
Attrition (final N): 12 M
Age: See table below for group characteristics
Ethnicity: Not mentioned
Other relevant demographics: None mentioned
Anthropometrics
| L group | H Group | |
| Age, yr | 27±3 | 33±4 |
| Ht, cm | 177.6±2.5 | 175.0±2.7 |
| Wt, kg | 71.5±1.3 | 73.2±2.0 |
| Body fat, % | 14.5±1.5 | 12.4±0.9 |
| VO2max, ml/kg/min | 58.9±3.7 | 57.5±3.3 |
Location: Lab, Dep Environmental and Occupational Medicine, University Medical School, Aberdeen, Scotland
|
Variables |
Group L |
Group H |
Group L,H Trial A |
Group L, H Trial B |
Group L, H Trial C |
Group L, H Trial D |
Statistical Significance of Group Difference |
|
Drink vol, ml |
|
746±17 758±33 |
1448±30 1522±58 |
2255±83 2243±72 |
2927±81 3180±142 |
p not reported |
|
|
Na intake mmol Cl intake, mmol K intake, mmol |
16.0±0.9, 47.2±1.9 7.5±1.1, 22.5±1.0 0.3±0.0, 0.2±0.1 |
29.8±0.5, 95.8±4.1 13.2±0.7, 45.2±1.8 0.4±0.1, 0.5±0.1 |
45.2±2.3, 143.7±6.7 21.8±0.8, 65.8±2.0 0.7±0.1, 0.9±0.2 |
62.0±2.6, 188.0±6.9 30.2±1.4, 90.0±4.6 0.8±0.2, 1.0±0.2 |
p not reported | ||
| Total Urine output, mL |
135 (114-240), 144 (124-162)
|
493 (181-731) 260 (137-376) |
867 (263-1191) 602 (350-994) |
1361 (1014-1984) 1001 (714-1425) |
ns, L>H in all trials p<0.05, trials B, D: L >H |
||
|
Mean body mass loss, kg, % |
1.48±0.02, 2.06±0.02 |
1.51±0.03, 2.07±0.03 | -- | -- | -- | -- |
ns, p=0.65 |
| Whole body net fluid balance, ml | 1490 (1382-1780) | 1555 (1299-1789) |
-909 (-1011--835) -958 (-1018--826) |
-- not reported -286 (-415--159) |
-128 (-441--380) 111 (-379-+394) |
-135 (-503-+426) 427 (-139-+828) |
p not reported |
|
Exercise duration, min |
38±2 |
37±3 | -- | -- | -- | -- |
ns, p=0.70 |
| Plasma vol change, % | 4.8±0.7 | 5.7±0.5 | -- | -- | -- | -- | p not reported |
Other Findings
NS differences in amts of Na excreted over study period (L: p=0.27; H, p=0.55). Cl excreted: ns differences between trials in either group (p=0.37). K: ns differences within group; trial D, greater amt K excreted by H vs L (p=0.002).
Blood and plasma changes: normal pre-ex values for hct, hgb, Sosm, K, Cl, Na. Post-exercise values<pre-ex values, though no diff between different trials or groups. NS diff between trials in Sosm for group H (P=0.44); group L, Osm lower in trials C and D than in trial A (pnot reported). Serum Na and Cl little affected by any treatment in group H (p=0.95, p=0.54). Group L, trials C, D, Na 7 Cl decreased after rehydration period. Serum-K unchanged throughout trials A and B for both groups.
Plasma hormones: measurements in A and D: ns diff between trials or between groups after exercise for vasopressin, aldostersone, angiotensinII.
palatability: ns differences between trials/groups.
Merely drinking a large volume of beverage after exercise-induced dehydration is not sufficient to acheive complete rehydration if the [Na] is insufficient
Ingesting a beverage with a high-[Na] is not sufficient to acheive complete rehydration if the volume consumed is not appropriate.
Both [Na] and volume of the beverage should be considered if optimal rehydration following exercise-induced dehydration is the goal.
| University/Hospital: | University Medical School (Aberdeen Scottland) |
See paper for figures showing time-course of Urine & plasma volume changes, net fluid balance.
* Very small sample size (and large range of response), led to inability to find differences on many variables (palatability, blood/plasma changes, fluid balance).
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Quality Criteria Checklist: Primary Research
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| Relevance Questions | |||
| 1. | Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies) | Yes | |
| 2. | Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? | Yes | |
| 3. | Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? | Yes | |
| 4. | Is the intervention or procedure feasible? (NA for some epidemiological studies) | Yes | |
| Validity Questions | |||
| 1. | Was the research question clearly stated? | Yes | |
| 1.1. | Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? | Yes | |
| 1.2. | Was (were) the outcome(s) [dependent variable(s)] clearly indicated? | Yes | |
| 1.3. | Were the target population and setting specified? | Yes | |
| 2. | Was the selection of study subjects/patients free from bias? | ??? | |
| 2.1. | Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study? | N/A | |
| 2.2. | Were criteria applied equally to all study groups? | N/A | |
| 2.3. | Were health, demographics, and other characteristics of subjects described? | Yes | |
| 2.4. | Were the subjects/patients a representative sample of the relevant population? | ??? | |
| 3. | Were study groups comparable? | ??? | |
| 3.1. | Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) | ??? | |
| 3.2. | Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? | ??? | |
| 3.3. | Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) | Yes | |
| 3.4. | If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis? | ??? | |
| 3.5. | If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.) | No | |
| 3.6. | If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? | N/A | |
| 4. | Was method of handling withdrawals described? | N/A | |
| 4.1. | Were follow-up methods described and the same for all groups? | N/A | |
| 4.2. | Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.) | N/A | |
| 4.3. | Were all enrolled subjects/patients (in the original sample) accounted for? | Yes | |
| 4.4. | Were reasons for withdrawals similar across groups? | N/A | |
| 4.5. | If diagnostic test, was decision to perform reference test not dependent on results of test under study? | N/A | |
| 5. | Was blinding used to prevent introduction of bias? | ??? | |
| 5.1. | In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? | ??? | |
| 5.2. | Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.) | Yes | |
| 5.3. | In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? | ??? | |
| 5.4. | In case control study, was case definition explicit and case ascertainment not influenced by exposure status? | N/A | |
| 5.5. | In diagnostic study, were test results blinded to patient history and other test results? | ??? | |
| 6. | Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? | Yes | |
| 6.1. | In RCT or other intervention trial, were protocols described for all regimens studied? | Yes | |
| 6.2. | In observational study, were interventions, study settings, and clinicians/provider described? | Yes | |
| 6.3. | Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? | Yes | |
| 6.4. | Was the amount of exposure and, if relevant, subject/patient compliance measured? | Yes | |
| 6.5. | Were co-interventions (e.g., ancillary treatments, other therapies) described? | N/A | |
| 6.6. | Were extra or unplanned treatments described? | N/A | |
| 6.7. | Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? | Yes | |
| 6.8. | In diagnostic study, were details of test administration and replication sufficient? | Yes | |
| 7. | Were outcomes clearly defined and the measurements valid and reliable? | Yes | |
| 7.1. | Were primary and secondary endpoints described and relevant to the question? | Yes | |
| 7.2. | Were nutrition measures appropriate to question and outcomes of concern? | Yes | |
| 7.3. | Was the period of follow-up long enough for important outcome(s) to occur? | Yes | |
| 7.4. | Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? | Yes | |
| 7.5. | Was the measurement of effect at an appropriate level of precision? | Yes | |
| 7.6. | Were other factors accounted for (measured) that could affect outcomes? | Yes | |
| 7.7. | Were the measurements conducted consistently across groups? | Yes | |
| 8. | Was the statistical analysis appropriate for the study design and type of outcome indicators? | Yes | |
| 8.1. | Were statistical analyses adequately described and the results reported appropriately? | Yes | |
| 8.2. | Were correct statistical tests used and assumptions of test not violated? | Yes | |
| 8.3. | Were statistics reported with levels of significance and/or confidence intervals? | Yes | |
| 8.4. | Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)? | N/A | |
| 8.5. | Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? | Yes | |
| 8.6. | Was clinical significance as well as statistical significance reported? | ??? | |
| 8.7. | If negative findings, was a power calculation reported to address type 2 error? | N/A | |
| 9. | Are conclusions supported by results with biases and limitations taken into consideration? | Yes | |
| 9.1. | Is there a discussion of findings? | Yes | |
| 9.2. | Are biases and study limitations identified and discussed? | Yes | |
| 10. | Is bias due to study's funding or sponsorship unlikely? | Yes | |
| 10.1. | Were sources of funding and investigators' affiliations described? | Yes | |
| 10.2. | Was the study free from apparent conflict of interest? | Yes | |