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Hydration and Physical Activity


Millard-Stafford ML, Sparling PB, Rosskopf LB, DiCicarlo LJ.  Carbohydrate-electrolyte replacement improves distance running performance in the heat, Med Sci Sports Exer 1992; 24(8): 934-40. 

PubMed ID: 1406180
Study Design:
Randomized Crossover Trial
C - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:

To evaluate the effects of a 7%CES (versus water) on physiological responses, hydration status, exercise performance in male distance runners during simulated outdoor 40-km road race under warm, humid conditions.

Inclusion Criteria:

training >65 km/week; completion of 32-km training run in previous month; use of programmed drinking during run training; informed consent.

Exclusion Criteria:

none mentioned.

Description of Study Protocol:

Recruitment not mentioned


 randomized, double-blind crossover study in field setting; 2 conditions assigned in counter-balanced fashion.

Blinding used (if applicable)

 Double-blind, randomized assignment of drink conditions.

Intervention (if applicable)

 During 40-km run, given 1 of 2 drink conditions:  water or 7% CES (250 ml/5 km, which was equivalent to dose of 0.75 l/h)

Statistical Analysis

 ANOVA with repeated measures; Student's t-test for dependent samples; sig level of P<0.05.

Data Collection Summary:

Timing of Measurements

 Instructed to consume typical pre-competition diet for 3d prior to 1st trial, and replicate this for the 2nd trial; no exercise during the 24h prior to trial. 

Day of trial, consumed water, but no solid food; 30 min prior to run, consumed 400 ml of either 7%CES or water.  Trial conducted outdoors in summer (25C-32C, 82%-62%RH change across test sessions from beginning to end of trial).  Temp between trials was not significant.

Trial:  5Km loop completed 8x for distance of 40 km.  2-4 runners tested during each session.  250 ml of drink administered every 5 km, RPE, temp, and HR recorded; break at 20 km for blood sample, weight.

At end of trial, drink beverage ad libitum during 30 min recovery period. 

Dependent Variables

  • RER and VO2 (Douglas bag method)
  • HR
  • RPE
  • body weight
  • Sweat rate (net change in body weight, corrected for fluid)
  • Core temp
  • Glucose, total pro, BUN 
  • Electrolytes and Hgb (reflectance spectrometry)
  • Plasma lactate (analyzer)
  • Hct
  • Posm (freezing point depression)
  • Pvol (from hgb, hct)

Independent Variables

 Drink condition:


7%CES: 5% glu, 2% fructose, 9.7 mmol/l Na and Cl; 5 mmol/l K.

Control Variables

 drink volume and timing, timing of measurments; distance of run

Description of Actual Data Sample:


Initial N: N=8M

Attrition (final N): N=8M

Age: see table below.

Ethnicity: not mentioned

Other relevant demographics: none mentioned.

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

Subject characteristics
Age (yr) 32.1±6.0
Ht (cm) 186.7±5.1
Wt (kg) 70.5±7.2
%Body fat 8.7±1.1
VO2max (ml/kg/min) 69.8±3.7
HRmax (bpm) 191.4±11.5
Training distance (km/wk) 86.6±19.2
Best marathon time (min) 156.4±17.4


 Outdoors; Atlanta, GA (summer season)

Summary of Results:



Total duration of run (water; CES)

20 km

(Water; CES)

40 km

(Water; CES)


(Water; CES)

Statistical Significance of Group Difference

Fluid intake (l/hr)

0.78; 0.79    



Body weight loss (%)


 -2.3; -2.5

-4.4; -4.5

 -3.9; -4.1

  NS between trials

Sweat rate (l/h) 1.8       NS

Urine output (kg)

0.1; 0.2    



Run time, first 35 km (min) 149±4.2; 149.9±5.0       NS
Performance during last 5 km (min) 24.4±1.5; 21.9±1.0*       *P<0.03 CES vs water


Other Findings

 No differences between the 2 drink trials for serum electrolytes, blood lactate, total pro, BUN, Osm, %change Pvol, RER, HR, RPE, blood pressure.

Blood glucose sig higher (P<0.01) throughout 40K and recovery during CES vs water.

%VO2max sig higher (P<0.05) at 5K when consuming water (70.4%) vs CES (66.6%)

Author Conclusion:

7% CES is similar to water as a fluid replacement drink interms of thermoregulation, maintenance of phsiological function, hydration status.  However, the 7% CES increased blood glucose and had a significant regogenic effect on prolonged running, and thus may confer a benefit to highly-trained marathoners competing in the heat.

Funding Source:
Government: NIH
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? N/A
  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? N/A
  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? 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? N/A
  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? N/A
  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