NAP: Competition (2007)

Citation:

Ivy JL, Res PT, Sprague RC, Widzer MO. Effect of a carbohydrate-protein supplement on endurance performance during exercise of varying intensity. Int J Sport Nutr Exerc Metab. 2003; 13: 382-395.

PubMed ID: 14669937
 
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 compare the effects of a carbohydrate and a carbohydrate-protein supplement on aerobic endurance performance.
Inclusion Criteria:
Trained cyclists between ages 22 and 30.
Exclusion Criteria:
  • None specifically mentioned
  • One subject was excluded because he could not complete the exercise protocol.
Description of Study Protocol:
  • Recruitment: Methods not specified
  • Design: Randomized crossover trial
  • Blinding used: Double-blind.

Intervention

  • Subjects exercised on three separate occasions at intensities that varied between 45% and 75% VO2max for three hours and then at 85% VO2max until fatigued
  • Supplements (200ml) were provided every 20 minutes and consisted of a placebo, a 7.75% carbohydrate solution, and a 7.75% carbohydrate-1.94% protein solution
  • Trials were spaced a minimum of seven days apart.

Statistical Analysis

Performance data were analyzed by one-way ANOVA for repeated measures. All other data were analyzed using two-way ANOVA (treatment x time) for repeated measures. Significant differences between means were determined by Least Squares Means analysis.

Data Collection Summary:

Timing of Measurements

  • Respiratory gases, heart rate and RPE were collected at the last three minutes of each exercise stage
  • Blood samples were collected prior to exercise, at the end of pre-determined exercise stages and at fatigue.

Dependent Variables

  • Heart rate was monitored with Polar Beat
  • Respiratory gases were collected and analyzed
  • Blood samples were analyzed for glucose, insulin, FFA, lactate
  • RPE based on Borg scale. 

Independent Variables

Supplements (200ml) were provided every 20 minutes and consisted of a placebo, a 7.75% carbohydrate solution and a 7.75% carbohydrate-1.94% protein solution.

Control Variables

Each subject kept diet and training logs so that daily physical activity and dietary patterns could be repeated prior to testing.
Description of Actual Data Sample:
  • Initial N: Nine trained cyclists, all male
  • Attrition: Nine
  • Age: Mean age, 27.3±1.3 years
  • Ethnicity: Not mentioned
  • Location: Texas.
Summary of Results:

Other Findings

  • Carbohydrate supplementation significantly increased time to exhaustion (carbohydrate 19.7±4.6 minutes vs. placebo 12.7±3.1 minutes, 55% increase in performance), while the addition of protein enhanced the effect of the carbohydrate supplement (carbohydrate-protein 26.9±4.5 minutes, 36% increase in performance over carbohydrate, P<0.05)
  • There were no differences in RPE, energy expenditure or heart rate between treatments
  • Respiratory exchange ratio was significantly lower, carbohydrate oxidation significantly reduced and fat oxidation significantly increased during the placebo treatment, compared to the carbohydrate and carbohydrate-protein treatments. There were no differences in respiratory exchange ratio, carbohydrate oxidation or fat oxidation between carbohydrate and carbohydrate-protein treatments.
  • Blood glucose and plasma insulin levels were elevated above placebo during carbohydrate and carbohydrate-protein supplementation, but no differences were found between the two treatments.
Author Conclusion:
  • In summary, we verified that providing carbohydrate supplementation during prolonged aerobic exercise would improve endurance performance. More importantly, we found that the addition of protein to a carbohydrate supplement provided an additional ergogenic effect.
  • Endurance performance was increased by an additional 36% with the addition of protein. The reason for this improvement is equivocal at this time, but could be related to the sparing or more efficient use of muscle glycogen, the maintenance of plasma amino acid levels as they relate to central fatigue or to anapleroic reactions and the retention of Krebs cycle intermediates.
  • Further research will be required to address this question.
Funding Source:
Industry:
Pacific-Health Laboratories Inc
Other:
University/Hospital: University of Texas
Reviewer Comments:
Inclusion and exclusion criteria and recruitment methods were not well-defined.
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? 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? 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