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Hydration

HYD: Assessing Hydration Status (2007)

Citation:

Kovacs EMR, Senden JMG, Brouns F.  Urine color, osmolality and specific electrical conductance are not accurate measures of hydration status during postexercise rehydration.  J Sports MEdicine and Physical Fitness Mar 1999; 39 (1): 47-53.

 
Study Design:
Diagnostic, Validity or Reliability Study
Class:
C - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:
To determine whether measurements of different urinary variables (color, specific electrical conductance (SEC), osmolality) at one-hour intervals, during the recovery phase after an acute exercise-induced dehydration, provide a useful index of hydration status and consequently of additional fluid requirements.
Inclusion Criteria:
Trained cyclists, voluntary informed consent.  No others mentioned.
Exclusion Criteria:
None mentioned
Description of Study Protocol:

Recruitment

 Not mentioned

Design

 Randomized cross-over design:  Subjects participated in 3 exercise tests on different days, at least 4d apart. 

Maximal work capacity determined on cycle ergometer before testing, to determine work load for each individual.

Testing began 2 hours after standardized breakfast and fluids;  Subject emptied bladder, was weighed.

Cycled  at 50% max work load in environmental chamber to dehydrate 3% of body mass.  This took about 100-120 min.  Subjects then weighed again.  Had 15 min before start of 6-hr recovery period (resting, controlled temp, drinking fluids ad lib (cola, mineral water, carb-electrolyte solution given in randomized order.).  After 3 hr recovery, given standardized lunch. 

 

Blinding used (if applicable)

 not mentioned (assumed?)

Intervention (if applicable)

Recovery period: Drinking fluids ad lib (cola, mineral water, carb-electrolyte solution given in randomized order.). 

Statistical Analysis

 Sig between treatments and over time:  Friedman's test, followed by Wilcoxon's signed-rank test to determine location of sig differences.  Bonferroni correction applied to adjust for multiple comparisons. Sig at p<0.05.

Correlations: Pearson's product moment corr coefficients between all measured variables.  r=o.65 considered high, 0.5 moderate, >0.35 low. 

Data Collection Summary:

Timing of Measurements

 Blood samples collected prior to exercise at 50% max work load, and after exercise (5 min cool-down).  Urine samples collected at end of each hour or recovery (T1-T6).

Dependent Variables

  • Blood:
  • Hct, Hgb (microcentrifugation, absorption spectrophotometer, respectively) --> plasma volume
  • Osmolality (freezing point depression)
  • Urine: 
  • Osmolality (freezing point depression)
  • SEC (Sparta 5 Tester)
  • Color (visual color gradation scale)
  • Rehydration level:
  • Body mass lost each hour after each tratment
  • Fluid intake
  • Urine output

 

Independent Variables

 Drink conditions:
Cola, mineral water, carb-electrolyte solution

Control Variables

 Food intake, temperature

Description of Actual Data Sample:

 

Initial N: 8 M, well-trained, healthy cyclists

Attrition (final N):

Age: 21.9±0.8

Ethnicity: not mentioned

Other relevant demographics:

Anthropometrics

Ht: 182.4±2.5 cm; Wt: 70.0±2.2 kg; Max work capacity: 392±12W

Location: Netherlands, Maastricht University

 

Summary of Results:

 

Variables

Cola

Mineral water

Carb-Electrolyte Sol

Statistical Significance of Group Difference

Body Mass pre-ex (kg)

70.0±2.2

69.8±2.2

70.3±2.3

ns

Body mass lost dur ex

 2.2±0.1

 2.3±0.1

2.2±0.1

ns

Hct pre-ex 43.3±0.8 43.7±0.9 45.1±0.2 ns
Hct post-ex

 45.8±1.0

 45.6±0.9

47.1±0.6

 not mentioned

Posm pre-ex 290±2 292±2 291±1 ns
Posm post-ex 302±2 302±2 302±3 not mentioned
Dehydration during ex (%) 3.2±0.1 3.4±0.1 3.2±0.1 not mentioned
Drink intake recovery (kg) 2.6±0.2 2.2±0.2 2.8±0.3 ns
Urine output, recovery (kg) 1.1±0.2* 1.0±0.2* 1.1±0.2**

*p<0.001

*p<0.05

Rehydration post-recovery (%) 65.6±8.6 53.3±4.0 75.2±5.8 ns

 

Other Findings

 Urine color at T1 was highly concentrated and light brownish; with progressive fluid consumption, urine output increased and urine became less concentrated and paler compared to T1 (P<0.001).

Lowest USEC, color density, and osm obtained at T3 (Urine output at highest level).  From T3 to T6, urine output decreased and urine became more concentrated and darker (p<0.001).

Urine output at specific times showed high neg correlation with urine color and osmol for all trials (p<0.001); moderate neg correlation for SEC (p<0.001).  Urine color positively correlated with USEC and osmol (p<0.001).  USEC and osmol positively correlated (p<0.001). 

Level of hydration showed very poor correlation with urine output, SEC, color, osmol (p>0.05).

Author Conclusion:

Low early post-exercise urine production led to concentrated dark colored urine.  Fluid consumption to rehydrate reversed this and led to more dilute urine.  Rate of urine output during postexercise period was highly correlated with Uosmol, SEC and color.  None of the measured variables showed good correlation with post exercise hydration level at any measurement time. 

Urine output, osmol, SEC, and color are poor indices to determine level of body hydration and need for fluid consumption during the 1st 6 hours after  exercise. 

Funding Source:
Industry:
Isostar Sports Nutrition, Novartis Nutriton
Food Company:
Pharmaceutical/Dietary Supplement Company:
Reviewer Comments:
Very small sample size, though agreeswith findings of previous study of hydration indices (Francesconi et al, 1987).
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
  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? No
  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? No
  2.2. Were criteria applied equally to all study groups? ???
  2.2. Were criteria applied equally to all study groups? ???
  2.3. Were health, demographics, and other characteristics of subjects described? No
  2.3. Were health, demographics, and other characteristics of subjects described? No
  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? N/A
3. Were study groups comparable? N/A
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) N/A
  3.1. 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? ???
  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.) N/A
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) 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? ???
  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.) 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")? No
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? No
  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.) ???
  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.) ???
  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? N/A
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? N/A
  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? N/A
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? N/A
  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? ???
  7.5. Was the measurement of effect at an appropriate level of precision? ???
  7.6. Were other factors accounted for (measured) that could affect outcomes? No
  7.6. Were other factors accounted for (measured) that could affect outcomes? No
  7.7. Were the measurements conducted consistently across groups? N/A
  7.7. Were the measurements conducted consistently across groups? N/A
  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? 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
  8.4. 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
  8.5. 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? ???
9. Are conclusions supported by results with biases and limitations taken into consideration? ???
  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? No
  9.2. Are biases and study limitations identified and discussed? No
  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