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HYD: Assessing Hydration Status (2007)


Zappe DH, Tankersley CG, Meister TG, Kenney WL. Fluid restriction prior to cycle exercise: effects on plasma volume and plasma proteins. Med Sci Sports Exerc. 1993;25(11):1225-30.

PubMed ID: 8289608
Study Design:
Diagnostic, Validity or Reliability Study
C - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:
To examine the effect of changing the initial plasma volume (PV) and total circulating protein (TCP), via 24-hr fluid restriction, on their subsequent regulation at rest and during cycle exercise in a warm environment
Inclusion Criteria:

Trained male cyclists

Exclusion Criteria:

No data

Description of Study Protocol:


 Not described


 Study of sensitivity and specificity of a diagnostic test (prospective, experimental)

Blinding used (if applicable)


Intervention (if applicable)

  • Hypohydration protocol: Refrained from drinking fluids, and only ate dry foods. Alcohol and caffeine were not allowed during the 24-hr period prior to each exercise test. Dietary records were kept to verify the compliance.
  • Euhydration protocol: Instructioned to drink copious amounts of water during the 24-hr peirod preceding the exercise test.
  • Exercise protocol: In a heat chamber (30 oC; 50-60% rh) subjects exercised in a semi-reclining position on a modified cycle ergometer (Monark). Three progressive, absolute exercise intensities performed for 20 min each for a total of 60 min, with a pedaling rate of 60 rpm. Subjects drank 200 ml of water ~30 min prior to each experiment for test preparation purposes, but no other fluids were provided during the test.

Statistical Analysis

  • Repeated measures analysis of variance. Student Newman Keul's post-hoc test.
  • Paired t-test were performed to determine significance at individual time points.
Data Collection Summary:

Timing of Measurements

Catheter was kept patent with a dilute (0.9% NaCl) heparin solution (100 USP to allow for repeated blood sampling at rest and at the end of each work intensity (at min 19, 39, and 59)

Dependent Variables

  • Plasma volume (PV): An absolute PV was calcuated from PV = [RCV x (1-hematocrit (Hct)] x (Hct)-1
  • Red cell volume (RCV: ): RCV was estimated using a carbon monoxide (CO) dilution technique
  • Urine osmolality (Uosm) and total protein concentration (TP): Assayed from serum aliquots

Independent Variables

 Hypohydration vs. Euhydration, during heat and exercise

Control Variables


Description of Actual Data Sample:

 Initial N: 9 (100% male)

Attrition (final N): 8

Age: 23

Ethnicity: No data

Other relevant demographics: VO2peak = 63 ± 4

Anthropometrics: No data

Location: US


Summary of Results:
 I. Changes as a result of the 24-hr fluid restriction prior to the heat and exercise

  Euhydration Hypohydration % Change
Weight (kg) 74.3 72.9* 2
PV (ml) 4246 3893* 8
RCV (ml) 2982 2961 1
Uosm (  436  985*  285
Total circulating protein (g)  304  283*  7

*P<0.05, significant difference between hypohydration and euhydration status
% Change = averaged individual % changes between hypohydration and euhydration status
II. Serum osmolality and total protein changes at rest prior to the heat exposure (-20 min), at the start of heat exposure (0 min), and at the end of each of the 3 exercise intensities


Time (min)

    -20 0 20 40 60
Osm ( Euhydration 290 291 291 294 298!
  Hypohydration 296* 295* 297* 299* 303*!
TP (g.dl-1) Euhydration 7.2 7.0 6.9 7.3! 7.8!
  Hypohydration 7.5 7.4* 7.5* 7.7* 8.1!

*P<0.05, significant difference between hypohydration and euhydration
!P<0.05, significant difference from preexercise (0 min)
  • Total circulating protein was significant lower at rest (0 min) and at the end of each exercise intensity in hypohydration with a difference of 31 g from euhydration at the end of exercise.
  • There was a significant (P<0.01) reduction in PV during exercise in euhydration (-472 ml) and hypohydration (-470 ml), but the PV loss was similar between hydration states.
Author Conclusion:

24-hr fluid restriction resulted in a significant reduction in both PV and TCP content.

In trained subjects, hypohydration induced by 24-hr fluid restriction does not affect the subsequent rate of PV loss during cycle exercise in a warm environment, despite differences in TCP content between hydration states.

"This implies that, during cycle exercise, hydraostatic forces (rather than oncotic forces) drive PV exchanges."

Funding Source:
University/Hospital: Pennsylvania University
Reviewer Comments:

8 subjects were included in the analyses but a total of 9 subjects were enrolled in the study. No information on the dropout.

Subjects' health status were not described. Presumed "healthy" because they are trained cyclists

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) N/A
  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? 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? N/A
  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? ???
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
  3.2. 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.) 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
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? Yes
4. Was method of handling withdrawals described? No
  4.1. Were follow-up methods described and the same for all groups? No
  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? No
  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? Yes
5. Was blinding used to prevent introduction of bias? No
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? N/A
  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? No
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
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? N/A
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? N/A
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? 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
  6.7. 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
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? N/A
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)? No
  8.6. Was clinical significance as well as statistical significance reported? Yes
  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