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Hydration and Physical Activity


de Carvalho MV, Marins JCB, Silami-Garcia E.  The influence of water versus CES hydration on blood components during a 16 km military march, Military Medicine 2007; 172 (1): 79-82.

PubMed ID: 17274272
Study Design:
Randomized Controlled Trial
C - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:

To identify and compare possible alterations in the variables (glu, Na, K, Hct, Hgb, RBC, lactic acid) and some urinary parameters, along with body weight, with the ingestion of 2 beverages (water and CES) during a 16 km military march.

Inclusion Criteria:

Healthy, male soldiers, no history of medical problems in the past 6 mo; no users of alcohol, drugs, medication of any kind.

Exclusion Criteria:

Medication, alcohol, drug use; medical problems in the past 6 mo

Description of Study Protocol:


 not mentioned


 Between-group randomized experiment using free-living subjects

Blinding used (if applicable)

 not mentioned

Intervention (if applicable)

 subjects randomized into 2 groups:  1 group ingested water, the other lemon-flavored CES (60 g/l CHO glu, sucrose, fructose; 45 mg Na; 12 mg K, 42 mg Cl)

*electrolyte concentrations stated as "mg", not mg/l*

Statistical Analysis

 T-test to compare first and second collections for both groups (inter-group and intra-group).  Sig level of P<0.05.

Data Collection Summary:

Timing of Measurements

12 h fast prior to testing.

200-250 ml CES or water every 15 min during a 16 km military field march (average speed 5 km/h, carrying 20kg load; 10 min rest for every 50 min exercise).  During rest no urination or ingest anything other than test beverage. 

Initial blood and urine samples 1 hr prior to march; standardized breakfast (540 kcal, 107.51 g CHO, 8.21g pro, 10.72 g fat);  weight recorded before and after march.

Final blood and urine samples obtained immediately after march.

Dependent Variables

  • Glu (spectrophotometer, enzymatic colorimetric method)
  • U-Na, K (selective electrolyte method)
  • Hct, Hgb (automated method w/3 reagents)
  • Lactic acid (enzymatic method)
  • UpH (refractometry)
  • U-Density (reactive tapes)
  • U-Aspect and color (visual)

Independent Variables

 water or CES consumed during march.

Control Variables

 Climate same for all subjects (21.3-29.4C, 69-92%RH)

Same activity (marching 16 km, 5 km/h, 20 kg load)

Standardized breakfast

Description of Actual Data Sample:


Initial N: N=26 male soldiers:  N=12 in water group; N=14 in CES group

Attrition (final N): N=26 male:  N=12 in water group; N=14 in CES group

Age: see table below

Ethnicity: not mentioned

Other relevant demographics: non mentioned

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

Subject Characteristics
  CES group, N=14 Water group, N=12
Age (y) 18.93±0.27 18.83±0.39
Ht (cm) 174±5.44 175.3±5.34
Wt (kg) 67.73±10.73 66.26±9.89
Body fat (%) 7.6±3.87 7.2±2.58



Summary of Results:



CES group

(pre-; post-)

Water group

(pre-; post-)

Statistical Significance of Group Difference

 Na (mmol/l)

 139.09±1.93*; 136.88±0.98

 138.49±1.52*; 137.39±1.48

 *P<0.05 vs post-ex.

 K (mmol/l)

 3.98±0.36; 3.84±0.34

 3.93±0.22*; 3.73±0.19

 *P<0.05 vs post-ex.

 Glu (mg/dl)

 82.25±4.99; 76.75±5.29

 79.21±4.38; 75.29±5.05


Hct (%) 44.24±2.66*; 43.59±2.53 44.36±2.15*; 42.84±1.92

 *P<0.05 vs post-ex.

Hgb (%) 14.29±0.94*; 14.04±0.82 14.56±0.76*; 13.96±0.64

 *P<0.05 vs post-ex.

RBC (106/nm3) 5.01±0.31*; 4.99±0.26 5.02±0.33*; 4.87±0.29

 *P<0.05 vs post-ex.

Lactate (mmol/l) 1.0±0.1*; 2.0±0.3 0.9±0.1*; 2.0±0.4

 *P<0.05 vs post-ex.


Other Findings

Body weight:  sig reduction on wt (P<0.05) of water (not CES) group (pre- to post-exercsise).  Average dehydration (%Body wt) of 0.62% for water and 0.09% for CES. 

No significant differences between (inter-group) water and CES for Na, K, glucose, Hct, Hgb, lactic acid, as well as urinary measures at any time point (pre- or post-exercise). 

Significant (P<0.05) differences between pre- and post-exercise within (intra-group) Water and CES groups for Hct, Hgb, RBC, lactic acid, K, Na.  Also for Urinary measures of color, density. 

Author Conclusion:

Changes in blood and urinary variables are similar, regardless of consuming water or CES during exercise. 

Funding Source:
Government: conselho nacional de desenvolvimento científico e tecnológico cnpq
Food Company:
Reviewer Comments:

Small sample, but interesting field research.

Urinary volume not measured 9due to field setting). 

All subjects adequately hydrated due to beverages (water or CES) administered. 

Stress of exercise may not have been enough to show meaningful effect. Fitness level (i.e. VO2max) not measured for subjects - mayhave been different among those with different levels of fitness - their reaction to the stress of exercise. 

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? ???
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? 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
  3.5. 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? ???
  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.) 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? ???
  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? ???
  7.6. Were other factors accounted for (measured) that could affect outcomes? No
  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)? No
  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? No
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