NAP: Recovery (2014)


Green MS, Corona BT, Doyle JA, Ingalls CP. Carbohydrate-protein drinks do not enhance recovery from exercise-induced muscle injury. Int J Sport Nutr Exerc Metab. 2008; 18 (1): 1-18.

PubMed ID: 18272930
Study Design:
Randomized Controlled Trial
A - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:

To investigate whether consuming a recovery beverage containing carbohydrate and protein or carbohydrate only immediately after novel eccentric exercise differentially affects the rate of recovery from exercise-induced muscle injury.

Inclusion Criteria:
  • Low to moderate level of aerobic activity (one to five hours per week)
  • Age between 18 and 35 years
  • "Low risk" classification as defined by the risk-categorization guidelines of the American College of Sports Medicine.
Exclusion Criteria:
Previously trained using eccentric concentrations (e.g., plyometric training).
Description of Study Protocol:


Recruitment methods not reported.


  • Participants reported to the laboratory on five separate occasions. They attended each experimental visit two to three hours post-prandial at the same time of day.
  • During the first visit, baseline measurements were obtained and participants performed a strength-test familiarization trial
  • During the second visit, participants performed a 30-minute intermittent downhill treadmill run to induce muscle injury. Participants were randomly assigned to a treatment group: Carbohydrate (CHO), Carbohydrate and Protein (CHO+PRO) or Placebo (PLA). Following the downhill run, they consumed a specific amount of treatment beverage as determined by their treatment group. They also completed an isometric quadriceps strength test and a soreness-assessment protocol. Blood samples were also taken at this time.
  • Participants attended three post-injury visits (one, two and three days post-injury). During each of these visits, a blood sample was taken and assessments of isometric quadriceps strength and muscle soreness were performed.

Blinding Used 

Treatment was administered in a double-blind manner.


Immediately after the downhill run and again at 30 and 60 minutes post-downhill run, participants consumed one of three recovery beverages: CHO, CHO+PRO or PLA.

  • The CHO beverage provided 1.2g carbohydrate per kg body weight in the first hour post-injury and 0.6g carbohydrate per kg body weight in the second hour post-injury, both of which were 6.0% carbohydrate solutions
  • The CHO+PRO beverage provided identical amounts of carbohydrate, in addition to 0.3g protein per kg body weight in the first hour post-injury and 0.15g protein per kg body weight in the second hour post-injury, both of which were 6.0% carbohydrate and 1.5% protein solutions
  • The PLA beverage was a non-caloric, artificially sweetened drink provided in amounts isovolumetric to the CHO and CHO+PRO beverages.

 Statistical Analysis

  • To achieve a power of 0.80 and an effect size of 10% with an expected standard deviation of 5%, this study would require six participants per group (18 participants total)
  • Maximal isometric quadriceps strength data were analyzed with a four-way ANOVA (group x leg x angle x time) with repeated measures on leg, angle and time
  • Lower extremity muscle soreness and serum CK activity data were analyzed with separate two-way ANOVAs (group x time) with repeated measures on time
  • Average rating of perceived exertion and total number of steps taken during downhill run were analyzed with separate one-way ANOVA
  • Statistical significance was determined at an alpha level of P<0.05
  • Bonferroni adjustment was applied to post hoc means-comparison tests.
Data Collection Summary:

Timing of Measurements

  • Participants' weight, height and body composition were measured during the first visit
  • Maximal isometric quadriceps strength and lower extremity muscle soreness were assessed immediately before and after the downhill treadmill run and on each subsequent recovery visit (one, two and three days post-injury). Blood samples were also collected at these times to determine serum CK activity.

Dependent Variables

  • Maximal isometric quadriceps strength: Measured with a isokinetic dynamometer
  • Lower extremity muscle soreness: Participants rated muscle soreness using a visual analog scale on which a score of zero corresponds to "no soreness" and a score of 100 corresponds to "very, very sore"
  • Creatine kinase: Measured via blood samples.

Independent Variables


Control Variables

  • Standardized injury protocol
  • Diet was not controlled or quantified, but participants were instructed to consume their normal diet during the course of the study
  • Participants were asked to refrain from consuming alcohol and caffeine for 12 hours before testing
  • Participants were advised to refrain from strenuous physical activity extraneous to the study and from treating symptoms of exercise-induced muscle injury (e.g., cryotherapy, nonsteroidal anti-inflammatory drugs, massage)
  • Each experimental group consisted of identical numbers of participants in each menstrual-cycle phase.
Description of Actual Data Sample:
  • Initial N: 18 (18 females, no males)
  • Attrition (final N): 18
  • Age
    • ?Total group: 24.6±3.3 years
    • CHO-PRO: 24.5±2.1 years
    • CHO: 23.7±1.6 years
    • PLA: 25.5±5.2 years.
  • Ethnicity: Not described
  • Other relevant demographics: All participants reported regular (two or three times per week) participation in light- to moderate-intensity whole-body resistance training.


  • Total group: 1.65±0.06m
  • CHO-PRO: 1.68±0.05m
  • CHO: 1.62±0.06m
  • PLA: 1.64±0.07m.
  • Total group: 61.3±6.8kg
  • CHO-PRO: 65.6±7.2kg
  • CHO: 59.8±2.6kg
  • PLA: 58.4±8.0kg.
Body mass index
  • Total group: 22.6±2.1kg/m2
  • CHO-PRO: 23.1±2.5kg/m2
  • CHO: 22.8±2.1kg/m2
  • PLA: 21.7±1.5kg/m2.
Body fat percentage
  • Total group: 28.7±5.5%
  • CHO-PRO: 29.6±8.0%
  • CHO: 28.8±3.1%
  • PLA: 27.6±5.1%.
Differences were not observed between groups for any of these measures (P>0.05).


Atlanta, GA.

Summary of Results:

Key Findings

  • There was no difference among groups for average RPE (P=0.74)
  • There was no effect of treatment on recovery of maximal isometric quadriceps strength (P=0.21). In all groups, maximal isometric strength was reduced compared with pre-injury by 20.6±1.5%, 17.2±2.3% and 11.3±2.3% immediately, one and two days post-injury, respectively (P<0.05).
  • The rating of muscle soreness was not different among treatment groups at any time-point (P=0.56). Muscle soreness peaked at two days post-injury (pre-injury vs. two-day, 3.1±1.0mm vs. 54.0±4.8mm; P<0.01).
  • Serum CK values were not different among treatment groups at any time-point (P=0.59). Serum creatine kinase peaked one day post-injury (pre-injury vs. one-day, 138±47U vs. 757±144U per L; P<0.01).
Author Conclusion:

Consuming a carbohydrate or carbohydrate-protein beverage immediately after a single bout of novel eccentric exercise resulting in moderate amounts of muscle injury does not enhance recovery of exercise-induced muscle injury above what is seen with a placebo beverage.

Funding Source:
Other: Not reported
Reviewer Comments:
  • Potentially inadequate participant numbers (despite power calculation): In CHO Group, there were two participants who exhibited a three-fold greater CK response than other members of the group. As a result, a large effect size was observed at one day post-injury. When the high responders were removed from analysis, the effect size was reduced to a moderate level. Thus, the variability introduced by the two high responders might falsely accentuate the treatment effect.
  • Study investigated effects of supplementation after only one bout of eccentrically biased contractions. It is possible that chronic supplementation will enhance recovery from repeated bouts of exercise-induced muscle injury.
  • It is possible that benefit of supplementation occurs, not immediately after injury, but in the days after injury induction, when strength recovery results from regeneration of protein. One potential explanation for the finding of no differential recovery rates among supplementation groups is that each participant presumably consumed an adequate diet in the days after injury, allowing for the same degree of recovery. Thus, the timing of supplementation immediately after exercise might not match the time course of injury recovery. It cannot be ruled out that participants consumed a suboptimal diet during the study. Dietary status was not assessed, so authors are unable to account for this possible confounding variable.
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? 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%.) 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? 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? ???
  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? ???
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? No
  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? ???
  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)? Yes
  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? Yes
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? ???
  10.1. Were sources of funding and investigators' affiliations described? No
  10.2. Was the study free from apparent conflict of interest? Yes