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Hydration and Physical Activity


Wong SH, Williams C. Influence of different amounts of carbohydrate on endurance running capacity following short term recovery. Int J Sports Med. 2000; 21: 444-452.

PubMed ID: 10961521
Study Design:
Randomized Crossover Trial
A - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:
To examine ingestion of differing levels of CHO during a four-hour recovery after prolonged running on subsequent running capacity.
Inclusion Criteria:

Not stated.

Exclusion Criteria:

Not stated.

Description of Study Protocol:
  • Recruitment: Not stated.
  • Design: Randomized crossover trial
  • Blinding used: Double-blind.


  • Preliminary test was used to assess VO2max and familiarize participant with protocol
  • Two trials, each consisting of two treadmill runs, spearated by at least seven days: Trial One consisted of a 90-minute run
  • The four-hour recovery period began after Trial One. A fixed volume of 150% of body mass lost during Trial One was consumed during recovery on both occasions.

Statistical Analysis

  • Student's T-test was used to analyze paired data
  • Two-way ANOVA for repeated measures on two factors (experimental treatment and time)
  • Tukey's post-hoc test was used to assess differences between means if a significant interaction was detected.
Data Collection Summary:

Timing of Measurements

70% VO2max run on treadmill for 90 minutes, followed by four-hour recovery and run to exhaustion at same speed on two occasions.

Dependent Variables

  • Performance time
  • Total volume ingested
  • Percentage rehydration
  • Changes in body mass
  • Blood samples analyzed for insulin, lactate, glucose.

Independent Variables

  • CHO or placebo beverage
  • In both conditions, participants consumed 770ml of 6.5% CHO 30 minutes after Trial One. Participants then consumed the CHO or placebo (CHO-free sweetened beverage) at 30 minutes for three hours during recovery (167g CHO vs. 59g CHO).

Control Variables

  • Three-day weighed diet records were collected and analyzed
  • Subjects were asked to eat the same diet during the same time before the second experiment.
Description of Actual Data Sample:
  • Initial N: Nine endurance-trained male runners
  • Attrition (final N): Nine
  • Mean age (±SEM): 34.3±2.4 years 
  • Ethnicity: Not stated.

Other Relevant Demographics (Mean±SEM)

  • Height: 180.0±1.5cm
  • Mass: 70.4±2.7kg
  • Maximum heart rate: 185±3 beats per minute
  • V02max: 58.9±2.3ml per kg per minute.


Not stated.

Summary of Results:



Placebo (Mean±SEM)

Statistical Significance of Group Difference

Run Time in Time Two (minutes)




Other Findings

  • Higher blood glucose and serum insulin concentrations were observed during recovery in the CHO trial (P<0.05)
  • The estimated contributions of CHO oxidation to total energy expenditure during Time One in the CHO and placebo trials were 55.8% and 54.6%, respectively (not significant)
  • During Time Two, the same estimations suggested that a greater proportion of the total energy expenditure was provided by CHO oxidation in the CHO trial (75.8%) than in the placebo trial (50.2%, P<0.05).
Author Conclusion:
  • In summary, the results of this study suggest that ingestion of 50g CHO immediately after prolonged exercise results in a similar endurance capacity after a four-hour recovery, as ingesting three times more CHO (approximately 167g CHO) over the same recovery period in rehydrated subjects
  • No differences in endurance running capacity after a four-hour recovery, when runners ingested either 167g or 59g of CHO.
Funding Source:
University/Hospital: Chinese University of Hong Chong, Loughbrough University (UK)
Reviewer Comments:

Inclusion criteria, exclusion criteria and recruitment methods were not specified.

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? ???
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
  2.2. Were criteria applied equally to all study groups? ???
  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? 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? 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")? N/A
4. Was method of handling withdrawals described? Yes
  4.1. Were follow-up methods described and the same for all groups? Yes
  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%.) 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
  4.5. 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.) Yes
  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? N/A
  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? ???
  6.8. In diagnostic study, were details of test administration and replication sufficient? N/A
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)? ???
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? N/A
  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? ???
  10.1. Were sources of funding and investigators' affiliations described? No
  10.2. Was the study free from apparent conflict of interest? Yes