EAL

NAP: Training (2007)

Citation:

Pizza FX, Flynn MG, Duscha BD, Holden J, Kubitz ER. A carbohydrate loading regimen improves high intensity, short duration exercise performance. Int J Sport Nutr. 1995; 5 (2): 110-116.

PubMed ID: 7670450

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 determine the effect of a high-carbohydrate vs. a mixed diet on high-intensity, short-duration run performance.

Inclusion Criteria:

Subjects were competitive runners who were already running between 50 and 80km per week.

Exclusion Criteria:

None specifically mentioned.

Description of Study Protocol:

Recruitment: Methods not specified
Design: Randomized crossover trial
Blinding used: Double-blind
Intervention: Mixed diet or experimental diet for a six-day period
Statistical analysis: A one-way repeated-measures ANOVA was used to evaluate differences between treatments for all dependent measures except lactate. Lactate was analyzed using a two-way repeated-measures ANOVA.

Data Collection Summary:

Timing of Measurements

Subjects completed a 15-minute submaximal run and a performance run to exhaustion after two dietary treatments
Training consisted of daily runs of 90, 40, 40, 20 and 20 minutes at approximately 75% of VO_2max
Day Six was a rest day, all measurements taken on Day Seven
Trials separated by a two- to three-week washout period.

Dependent Variables

Pre-exercise blood samples analyzed for lactate
Body weight
Submaximal VO₂
Heart rate monitored through radiotelemetry
Carbohydrate oxidation measured through gas analysis
Time to exhaustion.

Independent Variables

Mixed diet: 4.0±0.5g CHO per kg for six days
Experimental diet: 4.5±0.5g CHO per kg for three days, followed by 8.2±0.4g CHO per kg for three days
Subjects were given exchange lists and told to select food groups for the appropriate diet. Food was not provided but subjects were asked to record food intake.

Description of Actual Data Sample:

Initial N: Eight trained runners, all male
Attrition (final N): Eight
Age: Mean, 28.1±5.5 years
Ethnicity: Not mentioned.

Other Relevant Demographics

Mean height: 179.8±6.7cm
Mean weight: 78.4±11.2kg
Mean VO_2max: 59.5±4.9ml per kg per minute.

Location

United States.

Summary of Results:

	Mixed Diet, Days One to Six	High-CHO; Days One to Three	High-CHO; Days Four to Six
Energy intake	3,205±621	2,785.6±482	3,476.8±377
CHO (percentage)	40.0±3.9	52.4±10.6	73.0±5.7
CHO (g per kg per day)	4.0±0.5	4.5±0.5	8.2±0.4
Fat (percentage)	39.9±4.1	31.2±6.9	17.1±7.1
Protein (percentage)	19.7±2.6	18.1±3.2	11.2±3.2

Other Findings

Preexercise lactate, body weight, submaximal VO₂ and heart rate did not differ significantly between treatments
Carbohydrate oxidation during submaximal running was higher (P<0.05) after the high-carbohydrate diet than after the mixed diet (3.00±0.30 for mixed diet vs. 3.49±0.19g per minute for high-carbohydrate diet)
Time to exhaustion in the performance run was longer after the high-carbohydrate diet, compared to the mixed diet (high-carbohydrate diet, 303.88±19.8 vs. mixed diet, 280.46±23.26 seconds, P=0.032).

Author Conclusion:

The major finding of this study is that high-intensity short-duration run performance is improved following a carbohydrate-loading regimen
In conclusion, athletes involved in high-intensity short-duration exercise may benefit from a carbohydrate-loading regimen prior to competition or during their training
Further investigation is required to determine the mechanism for the improved performance following a high-carbohydrate diet.

Funding Source:

University/Hospital:

Texas Christian University, University of Toledo

Reviewer Comments:

Muscle glycogen not determined
Recruitment methods and inclusion and exclusion criteria were not well-defined.

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?	No
	2.2.	Were criteria applied equally to all study groups?	???
	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?		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?		???
	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?	???
	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?	???
	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)?	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?	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