EAL

NAP: Competition (2007)

Citation:

Palmer GS, Clancy MC, Hawley JA, Rodger IM, Burke LM, Noakes TD. Carbohydrate ingestion immediately before exercise does not improve 20 km time trial performance in well trained cyclists. Int J Sports Med. 1998; 19: 415-518.

PubMed ID: 9774209

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 evaluate the effects of carbohydrate intake on the performances of well-trained cyclists in a simulated 20-km time trial in moderate ambient conditions.

Inclusion Criteria:

Well-trained cyclists, all had been competing in licensed cycle races or triathlons for at least the two previous seasons.

Exclusion Criteria:

None specifically mentioned.

Description of Study Protocol:

Recruitment: All subjects had either participated in previous investigations or were fully familiarized with all of the testing apparatus and procedures before the experiment.
Design: Randomized crossover trial
Blinding used: Single-blind; lab tests.

Intervention (if applicable)

Subjects performed two experimental trials on an air-braked ergometry system, separated by three to seven days at the same time of day
On the day of trial, subjects ingested eight ml per kg body mass bolus of either 6.8g per 100ml commercial CHO-electrolyte beverage (39±4g CHO) or placebo
10 minutes after finishing the drink, subjects commenced a five-minute warm-up at 150W before commencing 20-km time trial.

Statistical Analysis

Statistical significance between values were assessed with paired Student's T-tests.

Data Collection Summary:

Timing of Measurements

Measurements made before, during and after exercise.

Dependent Variables

Heart rate measured using Polar Sports Tester heart rate monitor
Gas exchange measurements through use of Oxycon Alpha automated gas analysis system.

Independent Variables

Eight ml per kg body mass bolus of either 6.8g per 100ml commercial CHO-electrolyte beverage (39±4g CHO) or placebo 10 minutes prior to exercise
Subjects refrained from heavy exercise 24 hours prior to testing
Testing done three hours post-prandial
Subjects required to maintain a full training and dietary record for 24 hours prior and to follow same regimen for second trial.

Description of Actual Data Sample:

Initial N: 14 cyclists; 11 males, three females
Attrition (final N): 14
Age: 23.2±3.1 years
Ethnicity: Not mentioned
Location: South Africa.

Summary of Results:

Other Findings

The average power output (312±40 vs. 311±38W) and heart rate (171±6 vs. 171±5 beats per minute) during the two rides were not different
The performance times for both time trials were also the same (27:41±1.39 minutes for both)
There was no order effect of the two conditions.

Author Conclusion:

The main finding of the present study was that the ingestion of about 40g carbohydrate 15 minutes prior to exercise did not improve 20-km cycle time trial performance (lasting approximately 30 minutes) in well-trained subjects
Carbohydrate availability, in the form of circulating blood glucose, does not limit high-intensity exercise of this duration.

Funding Source:

Industry:

Erich Jaeger (u K) Ltd (Leicestershire UK), Bromer Foods (PTY) Ltd (South Africa)

Food Company:

Other:

Reviewer Comments:

Larger sample size than most studies in this area.

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?		N/A
	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?	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?	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?	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