EAL

NAP: Competition (2007)

Citation:

Saunders MJ, Kane MD, Todd MK. Effects of a carbohydrate-protein beverage on cycling endurance and muscle damage. Med Sci Sports Exerc. 2004; 36 (7): 1,233-1,238.

PubMed ID: 15235331

Study Design:

Randomized crossover trial

Class:

A - Click here for explanation of classification scheme.

Quality Rating:

POSITIVE: See Quality Criteria Checklist below.

Research Purpose:

To determine whether endurance cycling performance and post-exercise muscle damage were altered when consuming a carbohydrate and protein beverage vs. a carbohydrate-only beverage.

Inclusion Criteria:

Trained male cyclists who performed at least three days of cycle training per week and possessed a cycle ergometer VO_2peak of over 40ml per kg per minute
All subjects completed an informed consent document, Physical Activity Readiness Questionnaire and a comprehensive medical questionnaire to determine any risk factors associated with coronary artery disease before participating in the study
All subjects were asymptomatic and possessed fewer than two risk factors using ACSM guidelines.

Exclusion Criteria:

Excluded if not included above.

Description of Study Protocol:

Recruitment: Methods not specified

Design: Randomized crossover trial

Blinding used: Double-blind.

Intervention

Subjects rode a cycle ergometer at 75% VO_2peak to volitional exhaustion, followed 12 to 15 hours later by a second ride to exhaustion at 85% VO_2peak
Subjects consumed 1.8ml per kg body weight of randomly assigned carbohydrate (7.3% carbohydrate) or carbohydrate and protein (7.3% carbohydrate, 1.8% protein) beverage every 15 minutes of exercise and 10ml per kg body weight immediately after exercise
Subjects repeated protocol with another beverage seven to 14 days later.

Statistical Analysis

Power analysis was done and sample size was adequate
Dependent T-tests were used to determined differences in performance times between trials
Two-way (condition x time) repeated measures ANOVA with Tukey HSD post-hoc analyses was utilized to determine differences in CPK levels between trials.

Data Collection Summary:

Timing of Measurements

Metabolic measures, heart rate and RPE were obtained every 30 minutes of exercise
Blood samples were obtained at rest and every 30 minutes during exercise.

Dependent Variables

Body mass was measured using a physician's scale
VO₂, CO₂, RER and ventilation was measured using a metabolic cart
Heart rate was measured with a Polar heart rate monitor
Ratings of Perceived Exertion were measured using a Borg scale
Blood samples were analyzed for glucose, CPK and lactic acid.

Independent Variables

1.8ml per kg body weight of a randomly assigned carbohydrate (7.3% carbohydrate) or carbohydrate and protein (7.3% carbohydrate, 1.8% protein) beverage every 15 minutes of exercise and 10ml per kg body weight immediately after exercise
Beverages were matched for carbohydrate content but not calorie content
Subjects completed dietary records for three days prior to each trial.

Description of Actual Data Sample:

Initial N: 15 males
Attrition (final N): 15
Age: Mean, 20.9±3.3 years
Ethnicity: Not mentioned
Location: Virginia.

Summary of Results:

Other Findings

In the first ride (75% VO_2peak), subjects rode 29% longer (P<0.05), when consuming the carbohydrate and protein beverage (106.3±45.2 minutes), than the carbohydrate beverage (82.3±32.6 minutes)
In the second ride (85% VO_2peak), subjects performed 40% longer (P<0.05), when consuming the carbohydrate and protein beverage (43.6±12.5 minutes), than when consuming the carbohydrate beverage (31.2±8.7 minutes)
Peak post-exercise plasma CPK levels, indicative of muscle damage, were 83% lower (P<0.05) after the carbohydrate and protein trial (216.3±122.0U/L) than the carbohydrate trial (1,318.1±1,935.6U/L)
There were no significant differences in exercising levels of VO₂, ventilation, heart rate, RPE, blood glucose or blood lactate between treatments in either trial.

Author Conclusion:

In summary, administration of a carbohydrate beverage with additional protein calories resulted in significant improvements in cycling time to fatigue and reductions in post-exercise muscle damage (measured indirectly, using plasma CPK levels), in comparison with a carbohydrate-only beverage
Further research is necessary to determine whether these effects were the result of higher total caloric content in the carbohydrate and protein beverage or due to specific protein-mediated mechanisms
Regardless of the specific mechanisms, these findings may have important implications for endurance athletes because it suggests that the effective caloric concentration of sports beverages can be elevated in carbohydrate and protein beverages to a greater degree than the 6% to 8% typically observed in carbohydrate beverages.

Funding Source:

University/Hospital:

James Madison University

Reviewer Comments:

Beverages were not isocaloric
Power analysis showed sufficient sample size.

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%.)	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?	Yes
	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?	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