NAP: Recovery (2014)


Miller SL, Gaine PC, Maresh CM, Armstrong LE, Ebbeling CB, Lamont LS, Rodriguez NR. The effects of nutritional supplementation throughout an endurance run on leucine kinetics during recovery. Int J Sport Nutr Exer Metab. 2007; 17: 457-467.

Study Design:
Randomized Crossover Trial
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Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:

To compare the effects of consuming a carbohydrate and a mixed protein-carbohydrate beverage throughout an endurance-exercise bout on whole-body leucine kinetics during the recovery period after exercise. 

Inclusion Criteria:

Endurance-trained men running a minimum of 56km per week.

Exclusion Criteria:

Metabolic or cardiovascular abnormalities, gastrointestinal disorders or use of nutritional or sports supplements or anabolic steroids.

Description of Study Protocol:


From community.


  • Randomized crossover
  • Three exercise protocols during which a supplement was given during a two-hour endurance bout of running
  • The trial was separated by a seven-day washout for isotope-decay recovery. 


  • CHO drink (45g dextrose, 835ml bottled water and non-sweetened flavoring), milk (480ml skim milk, 355ml bottled water, flavoring and aspartame) and placebo [(PLA) bottled water, non-sweetened flavoring and aspartame]
  • CHO and protein drink provided approximately 170kcal
  • Supplement was drunk at 20 minutes, 40 minutes, 60 minutes and 80 minutes of endurance run in 200-ml amounts. 

Statistical Analysis

Treatment means were calculated for all variables and subjected to a three-way analysis of variance (ANOVA) with differences detected using Tukey's post-hoc analysis.

Data Collection Summary:

Timing of Measurements

Baseline, 120-minute and 15-minute intervals for one hour. 

Dependent Variables

  • Leucine kinetics: After exercise continuous infusion of 1-13C-leucine for 180 minutes with blood and two minute breath samples
  • Plasma 13C-KIC and 13C02 enrichments were determined by gas chromatography and isotope-ratio mass spectroscopy, respectively.

Independent Variables

CHO drink (45g dextrose, 835ml bottled water and non-sweetened flavoring), milk (480ml skim milk, 355ml bottled water, flavoring and aspartame) and placebo (bottled water, non-sweetened flavoring and aspartame).

Control Variables

  • A 120-minute run at a speed pre-determined to elicit an effort equal to 65% of individual VO2max
  • Ad libitum water during the run
  • Diet: Three-day food records at baseline and days leading up to each trial.
Description of Actual Data Sample:
  • Initial N: Five males
  • Attrition (final N): Five
  • Age: 22±1.0 years
  • Ethnicity: Not described
  • Other relevant demographics: 60±0.9ml per kg per minute VO2max
  • Anthropometrics: 178±3.0cm tall, 71±3.0kg body weight, 62±2.0kg fat-free mass
  • Location: Storrs, CT.
Summary of Results:


  • Energy intake for the three days before each trial and the single day before each study did not differ before or between subjects. Macronutrient composition of diets was the same for all subjects before all trials.
  • Steady-state conditions were achieved during recovery from exercise. Leucine rate of appearance (Ra) and non-oxidative leucine disposal (NOLD) were lower during recovery from milk-supplemented exercise than with PLA (Ra, 125.0±20.3mcmol vs. 154.2±17.2mcmo per kg per hour; NOLD, 89.4±20.5mcmol vs. 129.7±17mcmol per kg per hour; P<0.05). 
  • Leucine oxidation (Ox) was higher after the milk-supplemented run (35.6±1.9mcmol per kg per hour) than with either CHO (23.9±3.7mcmol per kg per hour) or PLA (24.5±2.9mcmol per kg per hour), P<0.05. Leucine kinetics did not differ between CHO and PLA.
Author Conclusion:
  • When compared with placebo, a decrease was observed in whole-body protein breakdown and synthesis and an increase in Ox, as evidenced by leucine kinetics during the recovery period after a milk-supplemented endurance run
  • Perhaps these data suggest a need for greater protein intake during exercise to observe favorable results with respect to whole-body protein utilization, given that the quantity provided in the current study was enough to elicit an increase in oxidation and suppress breakdown but not enough to support synthesis
  • Carbohydrate ingestion did not influence whole-body protein turnover.
Funding Source:
University/Hospital: University of Connecticut Research Foundation
National Dairy Council
Other non-profit:
Reviewer Comments:
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? Yes
  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? Yes
  2.2. Were criteria applied equally to all study groups? Yes
  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? Yes
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? N/A
  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%.) N/A
  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? N/A
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? N/A
  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.) N/A
  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? N/A
  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? N/A
  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