EAL

NAP: Training (2007)

Citation:

Burke LM, Hawley JA, Schabort EJ, St. Clair Gibson A, Mujika I, Noakes TD. Carbohydrate loading failed to improve 100-km cycling performance in a placebo-controlled trial. J Appl Physiol. 2000; 88: 1,284-1,290.

PubMed ID: 10749820

Study Design:

Randomized crossover trial

Class:

A - Click here for explanation of classification scheme.

Quality Rating:

NEUTRAL: See Quality Criteria Checklist below.

Research Purpose:

To examine the reported ergogenic action of carbohydrate-loading on cycling performance, tested on a reliable laboratory protocol that simulates the demands of competitive road racing and to exclude a possible placebo effect of this carbohydrate-loading on exercise performance.

Inclusion Criteria:

Endurance-trained cyclists and triathletes accustomed to riding for prolonged periods (three to four hours), riding between 250 and 500km per week.

Exclusion Criteria:

None specifically mentioned.

Description of Study Protocol:

Recruitment: Methods not specified
Design: Randomized crossover trial
Blinding used: Double-blind
Intervention: CHO-loading or placebo-controlled moderate-CHO diet for three days.

Statistical Analysis

Differences in the sprint times and sprint power outputs and in the glycogen concentrations were examined by using repeated-measures ANOVA, whereas glycogen utilization, total 100-km time and total power outputs were compared by using Student's T-tests
A Sheffe's post-hoc test was used to assess differences revealed by the ANOVA.

Data Collection Summary:

Timing of Measurements

Subjects performed two 100-km time trials on separate occasions one week apart, three days after either a CHO-loading or placebo-controlled moderate CHO diet
The time trials were interspersed with four four-km and five one-km sprints
Muscle biopsies were taken before and after time trials.

Dependent Variables

Muscle biopsies taken from vastus lateralis to determine muscle glycogen content
Exercise performance measured through time trials
Heart rate measured by SportTester HR monitor.

Independent Variables

CHO loading (nine grams CHO per kg per day) or placebo-controlled moderate CHO diet (six grams CHO per kg per day) for three days
CHO breakfast (two grams CHO per kg) was consumed two hours before each time trial
CHO drink (one gram CHO per kg) was consumed during the time trials
Individualized food plans were created and all foods supplied during the three days
Subjects were required to record actual food and fluid intake
Diets were not eucaloric.

Description of Actual Data Sample:

Initial N: Seven subjects, all male
Attrition (final N): Seven
Age: Mean, 28±4.5 years; range, 22-37 years
Ethnicity: Not mentioned

Other Relevant Demographics

Mean weight: 72.1±6.7kg
Mean VO_2peak: 63.9±4.7ml per kg per minute, 4.6±0.6L per minute

Location

South Africa.

Summary of Results:

	CHO loading	Placebo	P-Value
CHO, grams	646±54	419±35	<0.05
CHO, grams per kg	9.0±0.3	5.8±0.2	<0.05
Energy, kcal	4,149±315	2,726±202	<0.05
Protein, grams	110±7	88±6	<0.05
Fat, grams	126±9	79±7	<0.05
Water, grams	2,997±432	3,059±622	NS

Muscle Glycogen Concentrations	Pre-Exercise	Post-Exercise	Utilization
CHO loading	572±107	96±63	476±66.5
Placebo	485±128, P=0.05	55±28	431±116

Other Findings

Carbohydrate-loading significantly increased muscle glycogen concentrations (572±107 vs. 485±128mmol per kg dry weight for CHO-loading and placebo, P<0.05)
Total muscle glycogen utilization did not differ between trials nor did time to complete the time trials (147.5±10.0 and 149.1±11.0 minutes, P=0.4) or the mean power output during the time trials (259±40 and 253±40W, P=0.4).

Author Conclusion:

In summary, this study shows that a CHO-loading protocol that increased pre-exercise muscle glycogen concentrations resulted in a minimal effect on the performance of a 100-km time trial involving high-intensity sprints when CHO was ingested before and during the event
By preventing any fall in blood glucose concentration, CHO ingestion during exercise may offset any detrimental effects on performance of lower pre-exercise muscle and liver glycogen concentrations
Alternatively, part of the reported benefit of CHO-loading on subsequent athletic performance could have resulted from a placebo effect.

Funding Source:

Government:

Medical Research Council of South Africa

Industry:

SASKO Pty Ltd

Food Company:

University/Hospital:

University of Cape Town

Not-for-profit

Foundation associated with industry:

Reviewer Comments:

Recruitment methods, inclusion criteria and exclusion criteria were not well-described
Diets were not eucaloric
Performance may have been similar in groups based on ingestion of CHO during the ride
Authors note that power analysis would require 30 subjects; lack of significant differences could be due to small number of subjects.

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?		???
	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?	???
	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?	???
3.	Were study groups comparable?		N/A
	3.1.	Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT)	N/A
	3.2.	Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline?	N/A
	3.3.	Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.)	N/A
	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?		???
	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?	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