EAL

NAP: Competition (2007)

Citation:

Andrews J, Sedlock D, Flynn M, Navalta J, Ji H. Carbohydrate loading and supplementation in endurance-trained women runners. J Appl Physiol. 2003; (95): 584-590.

PubMed ID: 12716874

Study Design:

Randomized crossover trial

Class:

A - Click here for explanation of classification scheme.

Quality Rating:

POSITIVE: See Quality Criteria Checklist below.

Research Purpose:

The purpose of this study is to examine the combined effects of carbohydrate loading and supplementation as well as the effects of carbohydrates supplementation alone on metabolic, hematologic and performance variables in endurance-trained female athletes during prolonged exercise.

Inclusion Criteria:

Training history of at least 12 months of endurance-type physical activity at a frequency of four times per week and a duration of six to seven hours per week
Weight-stable (<2.5kg) for at least one year
Eumenorrheic with a normal cycle length of 23 to 38 days
On a dietary regimen in which carbohydrate intake was not above 65% of the total energy intake.

Exclusion Criteria:

Subjects with unstable eating tendencies (skipping meals on a daily basis, macronutrient deficiencies such as a no fat or no protein diet, etc.).

Description of Study Protocol:

Recruitment

Eight female athletes volunteered to participate in the study.

Design

Randomized, crossover latin square (counter-balanced design).

Blinding Used

Double-blind.

Intervention

Subjects completed each of the following three trials: No carbohydrate loading plus no carbohydrates supplementation (Placebo P); carbohydrate supplementation only (S); carbohydrate loading plus carbohydrate supplementation (L+S). Subjects performed one trial per month to allow each trial to be completed in the mid-follicular phase of the menstrual cycle.

Four days before each trial, subjects followed a prescribed diet (75% carbohydrates) from the L+S trial and a moderate carbohydrate (50% carbohydrates) diet before the S and P trials
Experimental beverages were adminstered in a double-blind fashion during the performance trials (subjects recieved a 6% carbohydrate solution or a sweetened placebo)
Six ml per kg of the solution was consumed before the start of exercise and then three ml per kg was consumed every 20 minutes throughout the exercise.

Statistical Analysis

A repeated-measures one-way ANOVA was used to determine the effects of the experimental treatments on performance time and total grams of carbohydrate oxidized
Blood lactate, glucose and glycerol values were analyzed using separate two-way ANOVA with repeated measures
Tukey's post hoc tests were used where appropriate
Friedman's non-parametric matched sample statistical test was conducted to test for a possible order or training effect
P<0.05.

Data Collection Summary:

Timing of Measurements

Finger tip blood sample was obtained after an overnight fast
Oxygen consumption, heart rate and RPE were measured every 30 minutes during the run, starting at minute 25
Subjective GI discomfort was obtained throughout the run
A finger tip blood sample was obtained every 20 minutes with the beverage administered immediately after the blood collection
No measurements were taken and no beverage was administered after approximately 13 miles of the 15 mile run
Post-run, subjects were weighed and a post blood sample was obtained after five minutes.

Dependent Variables

Oxygen consumption was measured with a Douglas Bag
RER with collected air
Heart rate was measured with a Polar heart rate monitor
RPE was measured with the Borg scale
GI discomfort was measured on a one to five likert scale
Glucose, glycerol and lactate were measured via a blood sample.

Independent Variables

Diet
During run beverage

Training diaries to ensure that the proper amount of training and the taper was followed through on
Diet records for the four days preceding each trial showed that CHO intake goals were achieved for each condition.

Description of Actual Data Sample:

Initial N: Eight females
Attrition (final N): 8
Age: 20 to 40 years
Ethnicity: Not mentioned.

Anthropometrics

Variable	Mean±SE
Height, cm	165.9±2.4
Weight, kg	61.4±2.3
V0₂max, ml per kg per minute	51.7±2.7
Max heart rate, beats per minute	192.1±2.9
Training history km per week days per week	52.9±3.36 4.9±4.9

Location

Purdue University, West Lafayette, IN.

Summary of Results:

Variables	Loading Plus Supplementation (L+S)	Supplement (S)	Placebo (P)	Signficant Difference
Carbohydrates consumed	72.8±2.0% (334.9±29 grams)	53.3±2% (238.2±15.3 grams)	52.3±1.2% (214.2±15.1 grams)	Significant between L+S and S and P (P<0.05)
Performance time (minutes)	134.4±6.3	132.5±6.3	136.6±7.9	No significant difference
Heart rate (beats per minute)	172.8±3.5	167.7±3.1	172.6±3.9	No significant difference
RPE	No data given	No data given	No data given	No significant difference
RER substrate utilization	0.92±0.01	0.91±0.01	0.89±0.01
Carbohydrate oxidation as a percentage of energy expenditure	71.3±3.8%	67.3±4.3%	59.2±4.6%	Significant difference (P<0.05) between L+S and S compared with P
Blood lactate (m/mol)	3.0±0.4	2.7±0.3	2.6±0.3	L+S was significantly higher (P<0.05) during exercise when compared to S and P

Other Findings

Blood glucose levels were significantly higher during the L+S trial at 40 minutes, 60 minutes, 100 minutes and post-exercise and during the S trial at 60 minutes, 80 minutes, 100 minutes and post-exercise, in comparison to the P trial
Glycerol was similar among groups before each run, however a significant treatment-by-time interaction was found in that glycerol levels were significantly higher at 20 minutes, 80 minutes, 100 minutes and post-exercise during the P trial, when compared with the L+S trial
Glycerol was also significantly higher at 80 minutes, 100 minutes and post-exercise in the P trial, compared with the S trial.

Author Conclusion:

No significant difference in performance time was found among the three different trials
Mean performance times of the S and L+S trials were approximately four and two minutes faster than the P trial (respectively), however these values did not reach significance
Post-hoc analysis revealed that it would have taken about 20 females to detect a performance difference. Therefore, a type II error is possible.
However, the fuel being utilized was significantly different between the three groups, suggesting that different metabolic responses were a result of dietary manipulation.

Funding Source:

Industry:

Gatorade Sports Science Institute

Food Company:

Reviewer Comments:

Even though there was the possibility of a type II error, we cannot assume that with a greater power a difference would be seen
Overall carbohydrate intake may not have been enough to promote adequate muscle glycogen and improving performance.

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?		N/A
	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?	No
	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?	N/A
	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)?	Yes
	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?	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