Hydration and Physical Activity
Recruitment Not mentioned
Design Experimental crossover design: 4 experimental trials, different beverage ingested during each trial
Blinding used (if applicable) Not mentioned
Intervention (if applicable) Each of 4 trials had 3 phases: Volume depletion (exercise in heat until ~2% body mass lost), volume repletion (ingestion of 1 of 4 fluids over 1h), and recovery (6h).
Statistical Analysis
Comparisons made after normality established. Repeated-measures ANOVA followed by 1-way ANOVA and Tukey's multiple range test or Kruskal Wallis and Mann-Whitney where appropriate. Significance level p<0.05.
Timing of Measurements: 4 trials, conducted on same day of week for 4 weeks (1 week between each trial); each trial 3 phases
Pre-experimental trial: 3 Preliminary trials: 1)determine VO2max; 2) Volume depletion procedures; 3) Full experimental procedure w/only a 2h recovery (to familiarize subject w/protocols)
Experimental trials: AM after overnight fast and ingestion of 500mL water 2h prior to start of experiment; rested for 15 at 24C, blood sample collected, urine sample collected; Showered and rinsed w/DI water, body mass taken; volume depletion on cycle in heat at 60% VO2max; each 5 min exercise period followed by 5 min restCylce covered w/polythene bag (free from electrolytes) to eneable sweat collection and electrolyte analysis; Volume depletion to 2% body weight loss, ranged from 30-70 min.
Post-exercise: washed w/DI water (collected in bag); Body mass taken; showered and dressed and seated in comfortable environment w/in 25 min of the end of exercise; seated at rest for 15 min, blood sample taken, urine sample collected.
Volume repletion: over following 60 min, consumed a drink containing 0, 25, 50, or 100 mmol/l Na plus 125 ml/l low-E lemon flavor. Different beverage consumed during each trial, but vol consumed was equivalent to 150% mass loss; blood samples collected at end of repletion period and at 1, 2, 4, 6 hr after; urine collected at end of repletion and at 1, 2, 3, 4, 5, 6 h after.
Dependent Variable
- Body mass
- Urine output and fluid balance
- Urine composition and electrolyte balance; Blood and serum measurements (Na, K: flame photometry, Cl: coulometric titration; Osm: freezing point depression)
- Sweat losses of Na, K, Cl (analysis of sweat and wash-water collected) - ion chromatography
Independent Variables
Beverages during volume repletion phase of trial containing 0, 25, 50, or 100 mmol/l Na plus 125 ml/l low-E lemon flavoring
Drink Composition
Trial 0 | Trial 25 | Trial 50 | Trial 100 | |
Na mmol/l | 1±1 | 25±2 | 50±1 | 102.4±4 |
K mmol/l | 0.6±0.1 | 0.6±0.2 | 0.5±0.1 | 0.6±0.1 |
Cl mmol/l | 1±0 | 24±1 | 25±1 | 24±2 |
Osm mosm/kg | 19±1 | 64±2 | 107±2 | 199±2 |
Control Variables
Controlled room temp during exercise (34C, 60-70%RH) and repletion/recovery (24C)
Depletion to loss of 2% Body mass
Exercise at 60% VO2max
Patterns of food intake and physical activity kept constant during study
COnsumed 500 ml water 2h prior to testing
Initial N:6 (4 M, 2 F)
Attrition (final N): 6
Age: 28±8 years
Ethnicity: not mentioned
Other relevant demographics: recreationally physically active, though not systematically training at time of study
Anthropometrics: Ht: 168±11 cm; Wt: 69.0±13.8 kg; VO2max: 53.8±5.9 ml/kg/min
Location: Lab, University Medical School, Foresterhill, Aberdeen, UK
Variables |
Trial 0 |
Trial 25 |
Trial 50 | Trial 100 |
Statistical Significance of Group Difference |
Body mass, kg |
1.28±0.44 |
1.29±0.29 |
1.31±0.40 | 1.36±0.38 |
ns, p=1.00 |
Sweat loss, mmol Na K Cl |
62.0±45.3 7.5±4.9 62.2±42.4 |
64.2±30.9 6.7±2.2 52.4±28.2 |
64.0±41.9 7.2±2.2 51.4±29.1 |
65.3±46.1 7.1±2.7 58.9±38.2 |
ns, p=0.999 ns, p=0.979 ns, p=0.939 |
Drink volume, ml |
1.912±653 |
1.938±433 |
1.968±595 | 2.035±569 |
ns, p not reported |
Electrolyte intake, mmol Na K Cl |
1.3±1.4 1.1±0.4 1.7±0.9 |
48.9±10.7 1.2±0.3 45.9±8.3 |
99.1±30.1 1.1±0.4 46.8±13.2 |
206.1±55.1 1.1±0.4 46.4±11.2 |
ns, p not reported |
Vol urine produced, ml | 1182±438 | 970±340 | 8 00±353 | 578±280 | p=0.033 |
Fluid balance, ml | -642±342* | -403±394** | -266±366** | +16±322 | sig, p not reported |
Ingested Na retained, % | n/a | 9 (-60-+60)* | 53 (2-83) | 72 (56-80) | * sig less tham trial 100, p=0.013 |
Whole body net Na balance, mmol | not reported | not reported | -13±29 | 75±40 | p not reported |
Other Findings
Urine Output & Fluid Balance: greatest urine output occurred over 1-h period ending 1h after end of vol repletion period (ns difference between trials, p=0.457). Over the 1h period ending 2h post-repletion, vol of urine output in trial 100 was sig less than trial 0, 25 (p=0.006). 3h after vol repletion, trials 50 and 100 were less than vol produced on trials 0, 25 (p=0.016). Ns diff in quantities Na in urine between trials. Uosm similar to Uvol.
Blood/serum measurements: Blood vol decreased w/vol depletion on all trials by 3.6±2.5% (p=0.782). Plasma vol changed in same manner, but w/larger magnitude (by 5.5±4.7%, p=0.556). Red cell vol decreased by 1.3±1.6% over all trials; with repletion, red cel vol increased on trial 0 (p=0.000), whereas on trial 100 there was no change from vol-depletion (p=0.637). Serum electrolytes and Osm little affected by any treatment.
The addition of Na to fluids ingested after exercise-induced volume depletion has a significant effect on the restoration and maintenance of whole-body fluid balance.
The quantification of sweat electrolyte losses during exercise and replacement in the postexercise recovery period has allowed calculation of whole body water and electrolyte balance, which has enabled the monitoring of the recovery of water and Na balance in this study.
The 100 mmol/l Na drink appears to maximize acute restoration of fluid balance, but its consequences on K levels must be considered undesirable in terms of whole body electrolyte balance for anything other than the short-term situations.
University/Hospital: | Loughborough University |
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 | |
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 | |
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 | |
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 | |
4. | Is the intervention or procedure feasible? (NA for some epidemiological studies) | Yes | |
Validity Questions | |||
1. | Was the research question clearly stated? | Yes | |
1. | Was the research question clearly stated? | Yes | |
1.1. | Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? | Yes | |
1.1. | 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 | |
1.2. | Was (were) the outcome(s) [dependent variable(s)] clearly indicated? | Yes | |
1.3. | Were the target population and setting specified? | Yes | |
1.3. | Were the target population and setting specified? | Yes | |
2. | Was the selection of study subjects/patients free from bias? | ??? | |
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? | Yes | |
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? | Yes | |
2.2. | Were criteria applied equally to all study groups? | Yes | |
2.2. | Were criteria applied equally to all study groups? | Yes | |
2.3. | Were health, demographics, and other characteristics of subjects described? | Yes | |
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? | ??? | |
2.4. | Were the subjects/patients a representative sample of the relevant population? | ??? | |
3. | Were study groups comparable? | Yes | |
3. | Were study groups comparable? | Yes | |
3.1. | Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) | N/A | |
3.1. | Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) | N/A | |
3.2. | Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? | Yes | |
3.2. | Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? | Yes | |
3.3. | Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) | Yes | |
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? | N/A | |
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? | N/A | |
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.) | N/A | |
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.) | N/A | |
3.6. | If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? | N/A | |
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. | Was method of handling withdrawals described? | N/A | |
4.1. | Were follow-up methods described and the same for all groups? | 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 | |
4.2. | 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 | |
4.3. | Were all enrolled subjects/patients (in the original sample) accounted for? | Yes | |
4.4. | Were reasons for withdrawals similar across groups? | N/A | |
4.4. | 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 | |
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. | 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? | ??? | |
5.1. | 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 | |
5.2. | 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? | N/A | |
5.3. | In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? | N/A | |
5.4. | In case control study, was case definition explicit and case ascertainment not influenced by exposure status? | N/A | |
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? | ??? | |
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. | 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 | |
6.1. | 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 | |
6.2. | 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 | |
6.3. | 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 | |
6.4. | 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 | |
6.5. | Were co-interventions (e.g., ancillary treatments, other therapies) described? | N/A | |
6.6. | Were extra or unplanned treatments 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 | |
6.7. | 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 | |
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. | 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 | |
7.1. | 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 | |
7.2. | 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 | |
7.3. | 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 | |
7.4. | 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 | |
7.5. | 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 | |
7.6. | Were other factors accounted for (measured) that could affect outcomes? | Yes | |
7.7. | Were the measurements conducted consistently across groups? | 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. | 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 | |
8.1. | 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 | |
8.2. | 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? | ??? | |
8.3. | Were statistics reported with levels of significance and/or confidence intervals? | ??? | |
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)? | 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)? | Yes | |
8.5. | Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? | Yes | |
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? | ??? | |
8.6. | 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 | |
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. | Are conclusions supported by results with biases and limitations taken into consideration? | Yes | |
9.1. | Is there a discussion of findings? | Yes | |
9.1. | Is there a discussion of findings? | Yes | |
9.2. | Are biases and study limitations identified and discussed? | 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. | Is bias due to study's funding or sponsorship unlikely? | Yes | |
10.1. | Were sources of funding and investigators' affiliations described? | Yes | |
10.1. | Were sources of funding and investigators' affiliations described? | Yes | |
10.2. | Was the study free from apparent conflict of interest? | Yes | |
10.2. | Was the study free from apparent conflict of interest? | Yes | |