NAP: Recovery (2014)


Betts JA, Toone RJ, Stokes KA, Thompson D. Systemic indices of skeletal muscle damage and recovery of muscle function after exercise: effect of combined carbohydrate-protein ingestion. Appl Physiol Nutr Metab. 2009; 34: 773-784.

PubMed ID: 19767814
Study Design:
Randomized Crossover Trial
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Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:

To examine whether ingestion of a carbohydrate supplement with additional protein can attenuate evidence of exercise-induced muscle damage relative to the ingestion of the carbohydrate fraction alone.

Inclusion Criteria:
  • Healthy young men
  • Highly trained with varying degrees of accustomedness to the exercise protocol.
Exclusion Criteria:
None specified.
Description of Study Protocol:


Not described.


  • The study adopted a repeated-measures crossover design in which each participant completed two trials in randomized and counter-balanced order
  • Each trial required participants to perform approximately 90 minutes of high-intensity exercise followed by a four-hour recovery period
  • Throughout the exercise and acute recovery, participants ingested a solution of either carbohydrate alone or a mixture of carbohydrate and protein
  • Trials were separated by approximately nine weeks.

Blinding Used

Single-blinded: Participants were blinded to the treatment. Pre-testing was conducted to ensure that solutions were successfully matched for taste, odor and consistency.


  • Throughout the exercise and recovery period, participants ingested a solution of either carbohydrate alone or a mixture of carbohydrate and protein. The solutions were provided in equal volumes (5.5±0.5 L), relative to each participant's body mass (BM).
  • The carbohydrate cencentration of 9% provided 1.2g per kg-1 BM per hour-1 of carbohydrates under both treatments, which equates to a total carbohydrate intake of 492±44g
  • The carbohydrate-protein mixture contained an additional 0.4g per kg-1 BM per hour-1 of whey protein isolate, providing 164±15g of protein (20% glutamine). The estimated amount of energy that the carbohydrate and carbohydrate-protein solutions made available for metabolism was 8,231±729kJ vs. 10,975±972kJ, respectively.
  • Participants ingested the first volume of prescribed solution (7.0ml per kg-1 BM) during the standardized warm-up. Immediately upon completion of the exercise protocol, participants were provided with the first of eight volumes of prescribed solution (6.7ml per kg-1 BM), to be ingested over the four-hour recovery period (53.6ml per kg-1 BM in total). Subsequent solutions were provied at 30-minute intervals. Participants were permitted 15 minutes to consume each volume.

Statistical Analysis

  • Post-hoc analyses revealed that the sample size of 17 used in the study provided approximately a 99% power at P≤0.05
  • Overall differences between experimental conditions were examined using a two-way (treatment x time) general linear model for repeated measures, with the Greenhouse-Geisser correction utilized for e<0.75 and the Huynh-Feldt correction adopted for less severe asphericity
  • Where significant F-values were identified, the Holm-Bonferroni stepwise correct was applied to determine the location of variance.
Data Collection Summary:

Timing of Measurements

  • Blood samples were obtained throughout and 24 hours after each trial to determine the systemic indices of muscle damage and inflammation
  • Expired gas samples were were obtained throughout and 24 hours after each trial to determine substrate metabolism
  • An isokinetic dynamometer was used to establish baseline measurements of peak isometric torque for knee flexors and extensors and hip flexors and extensors. Measurements were followed up at four, 24, 48 and 168 hours post-exercise.

Dependent Variables

  • Peak isometric torque for knee flexors and extensors and hip flexors and extensors (isokinetic dynamometer)
  • Serum myoglobin concentration (blood samples)
  • Serum creatine kinase activity (blood samples)
  • Serum lactate dehydrogenase activity (blood samples)
  • Serum interleukin-6 concentration (blood samples)
  • Serum interleukin-10 concentration (blood samples)
  • Serum interleukin-1 concentration (blood samples)
  • Serum C-reactive protein concentration (blood samples)
  • Perceived muscle soreness (subjective ratings using a one-to-10-point scale)
  • Serum insulin (blood samples)
  • Serum cortisol (blood samples)
  • Plasma urea (blood samples)
  • Blood glucose (blood samples)
  • Blood lactate (blood samples)
  • Perceived exertion (subjective ratings).

Independent Variables

Participants ingested a solution of either carbohydrate alone or a mixture of carbohydrate and protein throughout the exercise and acute recovery period.

Control Variables

  • Standardized exercise testing protocol
  • Timing of measurements
  • Hydration (urine samples were collected to ensure adequate hydration)
  • Diet (participants adhered to their normal diet during the study).
Description of Actual Data Sample:
  • Initial N: 17 (17 males, no females)
  • Attrition (final N): Seven
  • Age: 26±5 years 
  • Ethnicity: Not described.

Other Relevant Demographics

  • VO2max was 61±5ml per kg-1 per minute-1
  • Eight of the total cohort were highly trained cyclists; nine of the total cohort were highly trained team-sport players, sampled from a variety of sports (i.e., basketball, rugby, field hockey and lacross). Accordingly, the overall cohort were well matched in terms of aerobic capacity and worked at similar relative exercise intensities during the study, but the degree to which they were accustomed to the type of activity performed during the exercise varied considerably.


Body mass: 74±6.6kg

Bath, United Kingdom.

Summary of Results:

Key Findings

  • Muscle function: There was no difference in peak isometric torque between the carbohydrate and carbohydrate-protein treatments in either the magnitude or the time-course of this effect for any muscle group tested. The absence of treatment effects was consistent in both the highest and lowest responders, as evidenced by the strong positive correlations between treatments 24 hours after exercise in knee flexors (R=0.77; P<0.001), knee extensors (R=0.72; P<0.001), hip flexors (R=0.75; P<0.001) and hip extensors (R=0.75; P=0.001).
  • Muscle damage: There was no difference in serum myoglobin concentrations, serum creatine kinase activity and serum lactate dehyrogenase activity between the carbohydrate and carbohydrate-protein treatments at any time-point. The absence of treatment effects was consistent in both the highest and lowest responders for each variable, as evidenced by moderate to strong positive correlations between treatments for the post-exercise elevations in myoglobin (R=0.53; P=0.04) and lactate dehydrogenase (R=0.49; P=0.05) and for the 24-hour post-exercise peak in creatine kinase (R=0.69; P=0.004).
  • Inflammation: There was no difference in serum concentrations of interleukin-6 (IL-6), interleukin-10 (IL-10), interleukin-1 (IL-1) and C-reative protein between the carbohydrate and carbohydrate protein treaments. The absence of treatment effects was evidenced by moderate to strong positive correlations between treatments for the post-exercise peaks in IL-6 (R=0.53; P=0.03) and IL-10 (R=0.70; P=0.02), the peaks in IL-1 receptor antagonist after two hours of recovery (R=0.69; P=0.004) and, although not significant, the 24-hour peaks in C-reactive protein (R=0.420; P=0.12).
  • Muscle soreness: Participants' subjective ratings of perceived muscle soreness did not differ by more than a single point at any time-point and were not different between the carbohydrate and carbohydrate-protein treatments
  • Metabolic data: Serum insulin and urea concentrations were significantly higher (P<0.02) while ingesting the carbohydrate-protein solution, both during the exercise protocol and throughout the acute four-hour recovery period.

Other Findings

  • Participants' subjective ratings of perceived exertion were virtually identical between treatments 
  • The total volume of urine produced during recovery was significantly greater when carbohydrate alone was ingested (2,190±125ml vs. 1,797±99ml; P=0.01).
Author Conclusion:

Acute ingestion of carbohydrate with addiitonal whey protein isolate during and for four hours after strenuous exercise does not attenuate systemic indices of muscle damage and inflammation, nor does it restore muscle function more effectively than ingestion of a matched quantity of carbohydrate alone.

Funding Source:
GlaxoSmithKline Nutritional Healthcare
Pharmaceutical/Dietary Supplement Company:
Reviewer Comments:
Heterogeneous sample chosen so that conclusions could be generalized more broadly.
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? Yes
  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? Yes
  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? N/A
  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)? 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? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes