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Hydration

Hydration and Physical Activity

Citation:

Maughan RJ, Bethell LR, Leiper JB.  Effects of ingested fluids on exercise capacity and on cardiovascular and metabolic responses to prolonged exercise in man.  Experimental Physiology 1996; 81: 847-59.

PubMed ID: 8889482
 
Study Design:
Randomized Crossover Trial
Class:
C - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:

To examine the effects of the administration of water or dilute CES on exercise capacity and on the metabolic and cardiovascular response to exercise.

Inclusion Criteria:

healthy, physically active but not highly-trained; informed consent.

Exclusion Criteria:

none mentioned.

Description of Study Protocol:

Recruitment

 not mentioned.

Design

 randomized crossover, 4 conditions administered in latin-square design.

Blinding used (if applicable)

 latin-square design precluded blinding

Intervention (if applicable)

 4 conditions administered during exercise:

no drink or 100 ml/10 min of water; isotonic CES (200 mmol/l glu; 35 mmol/l Na;20 mmol/l K; 37 mmol/l Cl; 310 mOsm/kg); Hypotonic CES (90 mmol/l glu; 60 mmol/l Na; 25 mmol/l K; 45 mmol/l Cl; 20 mmol/l citrate; 240 mOsm/kg).

Statistical Analysis

 Friedmans' non-parametric 2-way ANOVA to test period and treatment effects.  Pairwise comparisons using Wilcoxon matched-paris signed rank test; Dubcan's multiple range test;  Sig level P<0.05.

Data Collection Summary:

Timing of Measurements

 Prior to testingL VO2max determined;

Test sessions:  after fast from 10PM previous evening, rest in seated position for 15 min, had cannula inserted for blood sampling (15 min intervals during test and at exhaustion); subjects cycled to exhaustion at 70% VO2max; 4 conditions administered during exercise:no drink or 100 ml/10 min of water; isotonic CES; Hypotonic CES. 

Expired gas samples collected at 15 min intervals during exercise; HR measured at rest and at 5 min intervals during exercise.

Dependent Variables

  • HR
  • O2, CO2 (paramagnetic and infrared analyzers)
  • RER
  • CHO-oxidation (from VO2)
  • Glucose
  • lactate
  • Hgb, Hct (cyanmethemoglobin method)
  • Pvol changes (dill & Costill)
  • Electrolytes (flame photometry, coulometric titration)
  • total pro (Biuret method)
  • Osm (freezing point depression)

Independent Variables

 4 conditions administered during exercise:

no drink or 100 ml/10 min of water; isotonic CES; or Hypotonic CES

Control Variables

 Drink volume; work rate; room temp (21±0.1C; 21±1% RH)

Description of Actual Data Sample:

 

Initial N: N=12 M, healthy, physically-active, but not highly-trained.

Attrition (final N): N=12 M

Age: 24±1 y

Ethnicity: not mentioned.

Other relevant demographics: none mentioned.

Anthropometrics (e.g., were groups same or different on important measures)

174±1 cm; 67.0±2.4 kg

Location:

 lab, Dept environmental and Occupational Medicine, University medical School, Foresterhill, Aberdeen, UK.

Summary of Results:

 

Variables

No drink

Water

Isotonic Hypotonic

Statistical Significance of Group Difference

Mean exercise time to exhaustion (min)

86.7

101.1*

119.0* 110.1*

no SEM given; *P<0.01, diff from no-drink

Change in Pvol at exhaustion (%)

 -6.7±1.3*

-3.5±1.2 

-1.5±1.1 -0.5±2.1

 *P<0.01 from other 3 trials

HR at exhaustion (bpm)

 172±9

170±12 

174±9 172±13

NS

Rectal temp at exhaustion (C) 38.9* 38.4 38.7 38.5 no SEM given; *P=0.05 from other 3 trials

RER(at 15 min; 60 min)

0.91±0.01; 0.89±0.02 0.89±0.01; 0.85±0.01* 0.92±0.03; 0.87±0.03 0.91±0.02; 0.89±0.03 *no P given; sig different from other 3 trials

 

Other Findings

 NS differences between treatments for total protein, Sosm, HR, blood glucose, blood lactate, CHO oxidation. 

Serum K higher (P<0.05) on Iso- and Hypotonic treatments than with no-drink and water. 

Author Conclusion:

Ingestion of CES can improve exercise performance even when the amount of added glucose is small, and that performance may also be enhanced (though, to a lesser degree) by ingestion of water. 

Funding Source:
University/Hospital: University of Aberdeen
Reviewer Comments:
Quality Criteria Checklist: Primary Research
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? 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
  2.3. Were health, demographics, and other characteristics of subjects described? Yes
  2.4. Were the subjects/patients a representative sample of the relevant population? 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) Yes
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? N/A
  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
  3.5. 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
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? Yes
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? 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.) 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
  5.5. In diagnostic study, were test results blinded to patient history and other test results? N/A
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