EAL

NAP: Competition (2007)

Citation:

Tsintzas OK, Williams C, Wilson W, Burrin J. Influence of carbohydrate supplementation early in exercise on endurance running capacity. Med Sci Sports Exerc. 1996; 28 (11): 1,373-1,379.

PubMed ID: 8933487

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 whether the ingestion of a carbohydrate-electrolyte solution during the first hour of treadmill running at constant speed delays the onset of fatigue by reducing the rate of muscle glycogen utilization.

Inclusion Criteria:

Male recreational runners.

Exclusion Criteria:

None specifically mentioned.

Description of Study Protocol:

Recruitment: Methods not specified
Design: Randomized crossover trial
Blinding used: Double-blind.

Intervention

Subjects ran at 70% VO_2max to exhaustion on three occasions one week apart
On two occasions, two carbohydrate-electrolyte solutions (5.5% and 6.9%) were ingested for the first hour of exercise. Water was then ingested until exhaustion.
On the third occasion, water was ingested throughout the run.

Statistical Analysis

A two-way ANOVA for repeated measures on two factors (experimental treatment and sampling time) was used to compare differences between cardiovascular changes and blood metabolites for all trials
Times to exhaustion, body weight changes and volumes of fluid ingested during the three trials were analyzed by one-way ANOVA for correlated data
Any significant differences shown were assessed by applying the Tukey post-hoc test.

Data Collection Summary:

Timing of Measurements

Blood samples and expired air samples were collected prior to the run, every 20 minutes without interrupting running and at exhaustion.

Dependent Variables

Expired air samples were collected through the Douglas bag method
Heart rate
Borg scale for perceived exertion
One-to-10 scale for perceived thirst
Blood samples were analyzed for ammonia, sodium, potassium, lactate, glucose, hemoglobin, hematocrit, changes in volume, FFA, glycerol, epinephrine, norepinephrine, insulin, cortisol and growth hormone.

Independent Variables

Three interventions: Two carbohydrate-electrolyte solutions (5.5% and 6.9%) were ingested for the first hour of exercise; water was then ingested until exhaustion. On the third occasion, water was ingested throughout the run
All meals were prepared and consumed in a laboratory.

Control Variables

All subjects were asked to refrain from heavy exercise and to consume a normal diet for two days prior to trials.

Description of Actual Data Sample:

Initial N: 11 male subjects
Attrition (final N): Nine of 11 completed all three trials
Age: Mean, 27.0±1.9 years
Ethnicity: Not mentioned
Location: United Kingdom.

Summary of Results:

Other Findings

Exhaustion times were: For water, 109.6±9.6 minutes; 5.5% (124.5±8.4 minutes); 6.9% (121.4±9.4 minutes)
There was no difference between the two carbohydrate trials, but time to exhaustion was longer only for the 5.5% trial, compared with water (P<0.05)
Average performance times for the combined results of the two carbohydrate trials were longer than the water trial
Carbohydrate ingestion resulted in higher blood glucose concentration (P<0.01) at 20 minutes in the 5.5% trial only and lower (P<0.05) serum growth hormone and plasma FFA and glycerol concentrations at 60 minutes, but not at exhaustion in both the 5.5% and 6.9% trials, compared to the water trial
Oxygen uptake, heart rate, RPE, thirst, blood lactate, plasma ammonia, electrolytes, catecholamines and serum insulin and cortisol concentrations were not different in the three trials

Author Conclusion:

In summary, our results showed that the ingestion of a 5.5% carbohydrate-electrolyte solution during the first hour of exercise resulted in an improved time to exhaustion, compared with water ingestion
Although no statistical difference was observed when the 6.9% carbohydrate-electrolyte solution was ingested, six subjects demonstrated an improved endurance capacity when the latter solution was provided. Therefore, it is reasonable to conclude that CHO ingestion during the first hour of exercise improves endurance capacity to a greater extent than water alone.
It seems that the sparing of muscle glycogen, rather than the maintenance of blood glucose and carbohydrate oxidation rate toward the latter stages of exercise, might have been responsible for this improvement in endurance running capacity.

Funding Source:

Industry:

Smith-Kline Beecham

Pharmaceutical/Dietary Supplement Company:

Reviewer Comments:

Inclusion criteria, exclusion criteria and recruitment methods were not specified.

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?		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?		???
	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?	???
	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?	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)?	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