EAL

NAP: Competition (2007)

Citation:

Earnest CP, Lancaster SL, Rasmussen CJ, Kerksick CM, Lucia A, Greenwood MC, Almada AL, Cowan PA, Kreider RB. Low vs high glycemic index carbohydrate gel ingestion during simulated 64-km cycling time trial performance. J Strength Cond Res. 2004; 18 (3): 466-472.

PubMed ID: 15320674

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 examine the relationship between low- and high-glycemic index CHO feedings and time to complete a 64-kilometer time trial.

Inclusion Criteria:

Endurance-trained amateur male subjects actively participating in local cycling races
Subjects ranged in experience from category II to category III cyclists and competitive triathletes
All subjects were actively training in their pre-season preparation phase and not currently involved in competitions.

Exclusion Criteria:

Participants were screened in advance to ensure that they were not taking any nutritional supplements that might interfere with carbohydrate metabolism.

Description of Study Protocol:

Recruitment: Subjects volunteered to participate
Design: Randomized crossover trial
Blinding used: Double-blind.

Intervention

Subjects ingested 15g of low-glycemic index (honey, GI=35), high-glycemic index (dextrose, GI=100) carbohydrate or artificially flavored placebo gel supplement every 16km for a 64-kilometer cycling time trial
Trials were separated by seven days.

Statistical Analysis

A three- (treatment condition) by-five (time, baseline and distance segments) repeated-measures ANOVA with a Fisher's least significant differences post-hoc analysis was used to examine average wattage output during each segment, average time to complete each segment and the average HR and RPE for each distance segment
Data for percentage difference was expressed as the mean and percentage difference of each variable.

Data Collection Summary:

Timing of Measurements

All variables were measured at baseline and each 16-kilometer segment of the course: 16km, 32km, 48km and 64km.

Dependent Variables

Maximal power output measured using Computrainer
Heart rate
Rate of perceived exertion
Time to complete each 16km segment
Blood samples analyzed for glucose and insulin.

Independent Variables

15g of low-glycemic index (honey, GI=35), high-glycemic index (dextrose, GI=100) carbohydrate or artificially flavored placebo gel supplement every 16km for a 64-kilometer cycling time trial
Subjects completed four-day nutritional diet logs prior to each trial.

Description of Actual Data Sample:

Initial N: Nine subjects
Attrition (final N): Nine
Age: Mean age, 30±1 years
Ethnicity: Not mentioned
Location: Tennessee.

Summary of Results:

	Total Time (Minutes)	Statistical Power	Effect Size
Placebo	131.3±3.9	--	--
Dextrose	128.3±3.8	0.08	0.77
Honey	128.8±3.5	0.08	0.76

	Wattage over last 16 Kilometers (Watts)	Statistical Power	Effect Size
Placebo	174.8±11	--	--
Dextrose	218.7±20	0.49	2.19
Honey	209.6±16	0.48	1.74

Other Findings

Our results showed no differences between groups for the time to complete the entire time trial (honey=128 minutes, 42 seconds ±3.6 minutes; dextrose=128 minutes, 18 seconds ±3.8 minutes; placebo=131 minutes, 18 seconds ±3.9 minutes) or any 16-kilometer segment. However, an analysis of total time alone may not portray an accurate picture of time trial performance under carbohydrate-supplemented conditions.
When the carbohydrate data were collapsed, the carbohydrate condition (128 minutes, 30 seconds) proved faster than placebo condition (131 minutes, 18 seconds; P<0.02).
Examining the percentage differences and 95% confidence intervals shows the two carbohydrate conditions to be generally faster, as the majority of the confidence interval lies in the positive range: Placebo vs. dextrose, 2.46% (95% CI, -0.69, 4.64); honey, 1.98% (95% CI, -0.30, 5.02). Dextrose vs. honey was 0.39% (95% CI, -3.39, 4.15).
Within-treatment analysis also showed that subjects generated more watts over the last 16km vs. preceding segments for dextrose (P<0.002) and honey (P<0.0004) treatments.
When the final 16-kilometer W was expressed as a percentage of pre-test maximal W, the dextrose treatment was greater than placebo (p<0.05).
A strong trend was noted for the honey condition (P<0.06), despite no differences in heart rate or RPE.

Author Conclusion:

The primary finding from our study is that the riders ingesting low- and high-glycemic index carbohydrates were capable of completing the last 16km of a simulated 64-kilometer time trial faster than under placebo conditions
In conclusion, we believe that the reader must consider several observations associated with this trial. These include consistent statistically significant within-carbohydrate treatment findings suggesting an improvement in performance with continual carbohydrate feedings during a 64-kilometer time trial effort. However, the small subtleties associated with overall time differences may not be fully elucidated because of the small sample size used in this trial.
We therefore recommend that similar investigations be performed with larger samples and that particular attention be given to the latter stages of the time trial, because some riders may increase power output during the final portions of this type of event
It further appears that honey can serve as an effective mixed CHO gel source.

Funding Source:

Government:

USDA

Industry:

National Honey Board

Food Company:

University/Hospital:

University of Memphis

Reviewer Comments:

Power analysis was not done
Data appears overanalyzed for statistically significant results.

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?	???
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?		???
	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?	???
	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?	No
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