NAP: Recovery (2014)
Beelen M, Van Kranenburg J, Senden JM, Kuipers H, Van Loon LJC. Impact of caffeine and protein on postexercise muscle glycogen synthesis. Med Sci Sports Exerc. 2012; 44 (4): 692-700.

To assess the effect of protein or caffeine co-ingestion on post-exercise muscle glycogen synthesis rates when optimal amounts of CHO (1.2g per kg-1 per hour-1) is consumed.
Male cyclist who cycled at least 100km per week-1 and had a training history of more than three years.
- Females
- Cycling less than 100km per week-1.
- Recruitment: Not described
- Design: Randomized crossover trial; three tests separated by at least one week
- Blinding used: Double-blind.
Intervention
- One of three beverages given in amounts of three ml per kg-1 every 30 minutes during recovery (randomized order):
- CHO only (CHO): 1.2g per kg-1per hour-1 CHO
- CHO+protein+leucine mixture (CHO+PRO): 1.2g per kg-1per hour-1 CHO with 0.2g per kg-1per hour-1 casein protein hydrolysate and 0.1g per kg-1per hour-1 leucine
- CHO+caffeine (CHO+CAF): 1.2g per kg-1per hour-1 CHO with 1.7g per kg-1per hour-1 caffeine.
- All drinks were flavored with 0.05g per L-1 sodium saccharinate, 0.9g per L-1 citric acid and 5.0g per L-1 cream vanilla flavor. CHO source was 50% glucose and 50% maltodextrin. Each drink was labeled with 0.32g per L-1 (U-13C6) glucose.
Statistical Analysis
- Plasma insulin and glucose responses were calculated as area under the curve
- A two-factor repeated-measures ANOVA with time and treatment as factors was used to compare differences between treatments over time
- In case of significant F-ratios, Bonferroni post-hoc tests were applied to locate the differences
- For non-time-dependent variables, a paired Student's T-test was used to compare differences between treatment and control
- The results from the questionnaires were analyzed by the Friedman non-parametric test.
Timing of Measurements
- Questionnaire at five, 175 and 355 minutes
- Blood samples at 15-minute intervals for the first 90 minutes of recovery and every 30 minutes after until 360 minutes
- Muscle biopsy at cessation of exercise and after the final blood sample.
Dependent Variables
- Gi symptoms and taste of beverage: Questionnaire using a 10-point scale (1=not al all, 10=very, very much; or 1=horrible, 10=very tasty, respectively)
- Muscle glycogen concentration and synthesis rates: Muscle biopsy from the middle region of the vastus lateralis muscle
- Plasma insulin, glucose, lactate, FFA, adrenalin and noradrenalin and caffeine: Blood samples.
Independent Variables
- CHO only (CHO)
- CHO+protein+leucine mixture (CHO+PRO)
CHO+caffeine (CHO+CAF) beverage.
Control Variables
- Standardized dinner the evening prior to testing
- No physical exhaustive labor or exercise and diet as constant as possible the two days prior to testing
- A food and activity diary kept during these two days was used to standardize food intake and physical activity before the second and third tests
- Abstinence from caffeine containing food and beverages for two days prior to tests
- Muscle glycogen depletion by intense exercise protocol on a cycle ergometer until pedaling speed could not be maintained at 70% Wmax after pedaling bouts at 90% and 80% Wmax
- Recovery of six hours.
- Initial N: 14 males
- Attrition (final N): 14
- Age: 24±1 years
- Ethnicity: Not described
- Other relevant demographics: Maximal workload capacity (Wmax), 387±11W; VO2max, 61.5±1.2ml per kg per minute
- Anthropometrics
- BW: 71.6±2.5kg
- Body mass index: 21.7±0.4km/m2.
- Location: The Netherlands.
Findings
- Total cycling time did not differ between experiments
- All drinks were well tolerated; 95±2% of the total volume of test drink (2.6±0.9 L) was ingested, with no differences between treatments. The main complaints of bloated feeling, belching and urge to urinate were no different between experiments, although the taste of the CHO+PRO was rated significantly lower than the the other two drinks (P<0.01).
- Plasma insulin was higher in CHO+PRO, compared with CHO (P<0.05). Plasma glucose did not differ between experiments. No differences in plasma [U-13C6] glucose enrichments were observed between treatments.
- Plasma lactate over time was lower in CHO+PRO vs. CHO (P<0.012). There were no differences between CHO and CHO+CAF.
- Plasma FF over time was higher in CHO+CAF vs. CHO (P<0.01). There were no differences between CHO and CHO+PRO.
- There were no differences between trials over time in plasma adrenalin. Plasma noradrenaline over time was lower in CHO+PRO vs CHO. There were no differences between CHO and CHO+CAF.
- Plasma caffeine increased significantly (P<0.01) in CHO+CAF and was below detection (P<0.05mg per L-1) in the other two trials
- Post-exercise muscle glycogen did not differ between experiments. After six hours of post-exercise recovery, muscle glycogen increased, but the concentrations were not significantly different between trials.
- Histochemical analyses of muscle biopsies revealed no differences in muscle glycogen content between trials or between Type I and Type II fibers. There was a significant correlation between mixed muscle glycogen, determined by PAS staining and muscle glycogen measured using biochemical assay, with a Pearson correlation coefficient of 0.24 (P<0.01).
Coingestion of an insulinotropic amino acid-protein mixture of caffeine does not further accelerate post-exercise muscle glycogen synthesis when an optimal amount of CHO (1.2g per kg-1 per h-1) is already ingested.
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? | N/A | |
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? | 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 | |