NAP: Competition (2007)

Citation:

Kang J, Robertson RJ, Denys BG, DaSilva SG, Visich P, Suminski RR, Utter AC, Goss FL, Metz KF. Effect of carbohydrate ingestion subsequent to carbohydrate supercompensation on endurance performance. Int J Sport Nutr. 1995; 5: 329-343.

PubMed ID: 8605519
 
Study Design:
Randomized crossover trial
Class:
A - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:
To examine the effect of carbohydrate ingestion following carbohydrate supercompensation on endurance performance during prolonged moderate-intensity exercise.
Inclusion Criteria:
Trained cyclists.
Exclusion Criteria:
None specifically mentioned.
Description of Study Protocol:
  • Recruitment: Methods not specified
  • Design: Randomized crossover trial
  • Blinding used: Double-blind.

Intervention

  • Subjects performed two trials at an initial power output corresponding to 71±1% of their peak oxygen consumption
  • During the trials, subjects ingested either a 6% glucose-sucrose solution (at rate of 0.6g per kg per hour) or an equal volume of artificially flavored and sweetened placebo every 20 minutes throughout exercise
  • Both trials were preceded by a six-day carbohydrate supercompensation procedure in which subjects undertook a depletion-taper exercise sequence in conjunction with a moderate- (50% CHO for first three days) and high-carbohydrate (70% for next three days) regimen
  • Trials were separated by at least two weeks.

Statistical Analysis

  • Dependent variables were analyzed using a two-way ANOVA (trial x time) with repeated measures
  • Dietary and training data was analyzed using two-way ANOVA (trial x day) with repeated measures
  • Significant interaction of main effects were followed by simple effect analysis using one-way ANOVA
  • Significant F-ratios followed by post-hoc comparisons using Tukey's procedure.
Data Collection Summary:

Timing of Measurements

  • Blood samples were drawn prior to exercise, every 20 minutes during exercise and at exercise termination
  • Heart rate, expired ventilation, oxygen consumption and respiratory exchange ratio all were measured immediately after each blood sampling.

Dependent Variables

  • Endurance performance was measured in total time of exercise
  • Blood samples were analyzed for hematocrit, glucose, glycerol
  • Heart rate was taken through electrocardiogram
  • Respiratory gases were measured through open-circuit gas spirometer system.

Independent Variables

  • During the trials, subjects ingested either a 6% glucose-sucrose solution or an equal volume of artificially flavored and sweetened placebo every 20 minutes throughout exercise
  • Moderate (50% CHO) for three days and high (70% CHO) for three days
  • Subjects completed dietary recalls for a six-day period.
Description of Actual Data Sample:
  • Initial N: Seven males
  • Attrition: Seven
  • Age: Mean age, 23±2 years
  • Ethnicity: Not mentioned
  • Location: Pennsylvania.
Summary of Results:

Other Findings

  • Performance time to exercise termination was longer following the carbohydrate trial than after the placebo trial (P<0.05)
  • In the first 80 minutes of exercise, glucose levels were not different between trials, but beginning at 100 minutes, plasma glucose concentrations were higher (P<0.05) during the carbohydrate trial than placebo trial. At exercise termination, plasma glucose concentrations were higher (P<0.05) following the carbohydrate trial than placebo trial (4.54±0.30 vs. 4.02±0.21mM).
  • Plasma glycerol concentrations gradually increased from the onset of exercise to termination during both carbohydrate and placebo trials.
  • Carbohydrate oxidation rate was higher in the carbohydrate trial, beginning at 100 minutes and at exercise termination (P<0.05). The estimated total amount of carbohydrates that was oxidized was higher during the carbohydrate trial than during the placebo trial (461±35g vs. 359±29g, P<0.05)
  • Fat oxidation rate did not differ between trials during the first 80 minutes. At 100 minutes, the fat oxidation rate was lower during the carbohydrate trial than the placebo trial (P<0.05), but was not statistically different at exercise termination.
  • During carbohydrate supercompensation, total caloric intake, percentage of calories from protein and percentage of calories from carbohydrates did not differ between trials, with the exception of the carbohydrate ingestion on testing days.
Author Conclusion:
  • The primary finding of this study was that following a six-day carbohydrate supercompensation procedure, carbohydrate ingestion during cycling at a moderate intensity extended endurance time to exhaustion by about 35 minutes, as compared to ingestion of a placebo.
  • In summary, carbohydrate ingestion during exercise, following carbohydrate supercompensation prior to exercise, exerts an additional ergogenic effect by preventing a decline in blood glucose concentration and maintaining carbohydrate oxidation during the later stages of moderate-intensity exercise. It is suggested that combining a regimen of carbohydrate supercompensation prior to exercise with carbohydrate ingestion during moderate-intensity exercise is more effective in improving endurance performance, in comparison to carbohydrate supercompensation alone.
Funding Source:
Industry:
Quaker Oats Company, Gatorade Sports Science Institute, Exercise Physiology Laboratory
Food Company:
University/Hospital: University of Pittsburgh
Reviewer Comments:
  • Inclusion criteria, exclusion criteria and recruitment methods were not specified
  • Muscle glycogen was not measured during the carbohydrate supercompensation period.
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? ???
  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? 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? 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? Yes
  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? 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)? N/A
  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? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes