EAL

NAP: Competition (2007)

Citation:

Achten J, Jeukendrup AE. Effects of pre-exercise ingestion of carbohydrate on glycaemic and insulinaemic responses during subsequent exercise at differing intensities. Eur J Appl Physiol. 2003; 88: 466-471.

PubMed ID: 12527979

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 investigate the glycemic and insulinemic responses during exercise at different intensities, 45 minutes after ingestion of a 75-gram CHO load.

Inclusion Criteria:

Moderately trained subjects, all club and county standard endurance athletes with a training background of at least three years.

Exclusion Criteria:

None specifically mentioned.

Description of Study Protocol:

Recruitment: Methods not described
Design: Randomized crossover trial
Blinding used: Not used; lab tests
Intervention: Subjects consumed 75 g glucose 45 minutes prior to 20 minutes of exercise at 40%, 65% or 80% maximal power output
Statistical analysis: Two-way general linear model for repeated measurements was used to identify differences between the three different trials. When a significant F-ratio was obtained, the Tukey post-hoc test was used to locate the differences.

Data Collection Summary:

Timing of Measurements

Blood samples collected before glucose ingestion, at 15-minute intervals at rest and five-minute intervals during exercise
During exercise, measurements of heart rate and breath-by-breath analysis of expired gas were performed continuously.

Dependent Variables

Blood samples collected for plasma glucose, insulin and lactate
Heart rate measured using radio telemetry heart rate monitor
Expired gas collection measured with automated gas analysis system.

Independent Variables

40%, 65% or 80% maximal power output
Food intakes and activity patterns recorded for day prior to trial.

Description of Actual Data Sample:

Initial N: Eight male subjects
Attrition (final N): Eight
Age: Mean, 26.4±2.9 years
Ethnicity: Not mentioned
Other relevant demographics: VO_2max, 58.4±1.9
Location: United Kingdom.

Summary of Results:

Other Findings

Trials were performed at 55%±1%, 77%±1% and 90%±1% VO_2max.
Plasma glucose concentrations were similar during exercise at all three intensities. There was a significant main effect of time (P<0.05); the glucose concentration increased significantly during the first 15 minutes of rest. At the onset of exercise, plasma glucose concentration returned to pre-ingestion levels.
30 minutes after the ingestion of the glucose drink, insulin concentration was more than three times higher than at rest, on average 57±7, compared to 16±1microU per ml. During exercise, the concentration decreased to fasting levels and after 10 minutes of exercise the concentration became steady.
During exercise, plasma glucose concentrations decreased during the first five minutes of exercise and then stabilized in all trials at concentrations that would not be considered to be hypoglycemic
There were no significant differences in glucose or insulin concentrations between the three trials during exercise.

Author Conclusion:

In summary, this study showed no differences in plasma glucose or insulin concentrations during exercise at intensities ranging from 55% to 90% VO_2max
Furthermore, an equal number of subjects developed rebound hypoglycemia during low-, moderate- and high-intensity exercise.

Funding Source:

University/Hospital:

University of Birmingham

Reviewer Comments:

Inclusion and exclusion criteria not well-defined and recruitment methods not described
No power calculations done; small sample size
45-minute rest period prior to exercise may have resulted in no differences.

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?		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?	N/A
	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?		???
	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?	???
	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?		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?	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