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NAP: Recovery (2007)

Citation:

Van Loon LJC, Saris WHM, Kruijshoop M, Wagenmakers AJM. Maximizing postexercise muscle glycogen synthesis: carbohydrate supplementation and the application of amino acid or protein hydrolysate mixtures. Am J Clin Nutr. 2000 Jul; 72 (1): 106-111.

PubMed ID: 10871568
 
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 investigate whether an increase in carbohydrate intake, ingestion of a mixture of protein hydrolysate and amino acids in combination with carbohydrate or both, results in higher post-exercise muscle glycogen synthesis rates than does ingestion of 0.8g per kg per hour carbohydrate, provided at 30-minute intervals.
Inclusion Criteria:
  • Trained cyclists or triathletes
  • Subjects trained more than three times per week for over two hours and had a training history of more than five years.
Exclusion Criteria:
None specifically mentioned.
Description of Study Protocol:
  • Recruitment: Methods not specified.
  • Design: Randomized crossover trial
  • Blinding used: Double-blind.

Intervention

On three occasions separated by one week, after participating in a strict glycogen-depleting protocol, subjects received a beverage every 30 minutes to ensure ingestion of either 0.8g CHO per kg per hour (CHO trial), 0.8g CHO per kg per hour plus 0.4g wheat protein hydrolysate plus free leucine and phenylalanine/kg/hour (highly insulinotropic, CHO+protein trial) or 1.2g CHO per kg per hour (CHO+CHO trial).

Statistical Analysis

  • Plasma glucose and insulin responses were calculated as areas under the curve minus baseline values
  • The effect of each treatment on the glucose and insulin responses, glycogen synthesis rate and glycogen synthase activity was compared with that of the control trial by using paired T-tests with Bonferroni correction.
Data Collection Summary:

Timing of Measurements

  • Muscle biopsies taken immediately after strict glycogen-depleting protocol and after five hours of recovery
  • Blood samples taken at 30 minutes intervals until 300 minutes.

Dependent Variables

  • Muscle biopsies taken from vastus lateralis for glycogen content and glycogen synthase activity
  • Blood samples analyzed for plasma glucose and insulin.

Independent Variables

  • Subjects received a beverage every 30 minutes to ensure ingestion of either 0.8g CHO per kg per hour (CHO trial), 0.8g CHO per kg per hour plus 0.4g wheat protein hydrolysate plus free leucine and phenylalanine per kg per hour (highly insulinotropic, CHO+protein trial) or 1.2gCHO per kg per hour (CHO+CHO trial)
  • Subjects were informed to refrain from any sort of heavy physical labor and to eat the same meals the day before each of the trials.
Description of Actual Data Sample:
  • Initial N: Eight cyclists, all male
  • Attrition (final N): Eight
  • Age: Mean, 24.0±0.6 years 
  • Ethnicity: Not mentioned
  • Location: Netherlands.
Summary of Results:

Other Findings

  • Post-exercise glycogen content did not differ between trials
  • Plasma insulin responses in the CHO+protein and CHO+CHO trials were higher than those in the CHO trial (88±17% and 46±18%, P<0.05)
  • Muscle glycogen synthesis was higher in both CHO+protein and CHO+CHO trials than in the CHO trial (35.4±5.1mcmol and 44.8±6.8mcmol, compared with 16.6±7.8mcmol glycosyl units per gram of dry weight per hour, respectively; P<0.05)
  • No significant increase was observed in active form, total activity or the percentage of active glycogen synthase enzyme between the CHO+protein or CHO+CHO trial and the CHO trial at five hours post-exercise.
Author Conclusion:
  • The main conclusion to be derived from this study is that ingestion of a mixture of wheat hydrolysate and free leucine and phenylalanine in combination with CHO can results in an 88% higher post-exercise insulin response than can the intake of CHO only
  • At a CHO intake of 0.8g per kg per hour, provided at 30-minute intervals, addition of this insulinotropic mixture resulted in a significant increase in glycogen synthesis rates (113%) during the five-hour post-exercise period
  • An increase in the CHO ingestion rate up to 1.2CHO per kg per hour provided at 30-minute intervals also resulted in faster muscle glycogen synthesis (170%) than did an intake of 0.8g per kg per hour.
Funding Source:
Industry:
Quest International (Naarden Netherlands)
Reviewer Comments:
  • Inclusion criteria, exclusion criteria and recruitment methods were not well-defined
  • Only two of the three trials were isoenergetic.
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