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NAP: Competition (2007)

Citation:

Anantaraman R, Carmines AA, Gaesser GA, Weltman A. Effects of carbohydrate supplementation on performance during 1 hour of high-intensity exercise. Int J Sports Med, 1995; 16 (7): 461-465.

PubMed ID: 8550255
 
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 whether CHO before (as compared to both before and during) exercise enhances endurance performance when subjects perform high-intensity cycle ergometry exercise over a fixed one-hour period.
Inclusion Criteria:
Moderately trained subjects.
Exclusion Criteria:
None specifically mentioned.
Description of Study Protocol:

Recruitment

  • Methods not described.

Design

  • Randomized crossover trial.

Blinding Used

  • Double-blind.

Intervention

High intensity exercise tests were completed under three conditions:

  • Pre-exercise glucose polymer or placebo during exercise
  • Glucose polymer before and during exercise
  • Placebo before and during exercise.

Statistical Analysis

ANOVA with repeated measures was utilized to determine whether significant differences existed within and between treatments. Tukey's post-hoc procedures were used to identify significant mean differences. For power output, VO2 and RPE, average values over 10-minute time blocks were analyzed.

Data Collection Summary:

Timing of Measurements

During each test, subjects ingested a sweetened beverage four times: Two minutes before the test and at 15, 30 and 45 minutes. Ventilation, pulmonary gas exchange and heart rate data were collected continuously during the endurance performance ride. Blood samples were drawn at rest and every five minutes during exercise. RPE was recorded every five minutes.

Dependent Variables

  • Peak VO2 was determined using a continuous incremental protocol on a Monark cycle ergometer
  • High-intensity endurance performance tests on Monark cycle ergometer
  • Ventilatory and pulmonary gas exchange variables were collected using standard open circuit spirometric techniques
  • Heart rates were determined electrocardiographically
  • Blood samples were analyzed for glucose concentration
  • Ratings of perceived exertion were measured using the Borg Scale.

Independent Variables

  • 300ml glucose polymer solution or sweetened placebo were consumed immediately before or every 15 minutes during one hour of exercise
  • Subjects were instructed to maintain normal dietary and exercise patterns for the duration of the study.
Description of Actual Data Sample:
  • Initial N: Five subjects, three males, two females
  • Attrition (final N): Five
  • Age: Mean age 28.5±1.5 years
  • Ethnicity: Not mentioned
  • Location: Virginia.
Summary of Results:

Other Findings

  • No differences in power output were observed among the three treatments until at 40 to 60 minutes, where power output was greater with the glucose polymer.
  • This resulted in significantly greater total work and less drop-off in power output with glucose polymer consumption (619±234kJ for pre-exercise glucose and placebo during exercise and 599±235kJ for glucose before and during exercise), compared with placebo consumed before and during exercise (560±198kJ, P<0.05).
  • VO2 followed a similar pattern with no differences in VO2 over minutes zero to 40, significantly higher VO2 in pre-exercise glucose and placebo during exercise and a trend for higher VO2 in glucose before and during exercise during minutes 40 to 60, compared to placebo (P<0.05).
  • There were no differences between conditions for ratings of perceived exertion.
Author Conclusion:

The major findings of the present study are:

  1. Ingestion of glucose polymer results in significantly less drop-off in total power output during high-intensity cycle ergometer endurance performance of one hour duration, with the effect most demonstrable after 40 minutes of exercise
  2. Ingestion of carbohydrates prior to exercise (30g total) and ingestion of carbohydrates prior to and during exercise (120g total) were both equally effective in maintaining power output.

In summary, the results of the present study indicate that pre-exercise ingestion of 30g of glucose polymer in a 10% solution results in less drop-off in power output during one hour of maximal effort cycle ergometer endurance performance. This was demonstrable only during the final 20 minutes of exercise. No further benefit is observed when the same amount of carbohydrates is also ingested every 15 minutes during exercise.

Funding Source:
University/Hospital: University of Virgina
Reviewer Comments:
  • Inclusion and exclusion criteria and recruitment methods were not well-defined
  • Authors note that they did not control for dietary intake.
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? ???
  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? 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)? 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