EAL

NAP: Competition (2007)

Citation:

Moseley L, Lancaster GI, Jeukendrup AE. Effects of timing of pre-exercise ingestion of carbohydrate on subsequent metabolism and cycling performance. Eur J Appl Physiol. 2003; 88: 453-458.

PubMed ID: 12527977

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 metabolic and performance responses to the ingestion of carbohydrate at differing times before exercise.

Inclusion Criteria:

Endurance-trained men, all subjects were at least club-level cyclists
All subjects were healthy as assessed from responses to general health questionnaire.

Exclusion Criteria:

None specifically mentioned.

Description of Study Protocol:

Recruitment: Subjects volunteered
Design: Randomized crossover trial
Blinding used: Single-blind; lab tests.
Intervention: On three occasions separated by seven-day periods, subjects ingested 75g glucose dissolved in 500ml water, resting for 15, 45 or 75 minutes before exercising for 20 minutes at 65% maximal power output followed by a time trial.

Statistical Analysis

Data from three trials analyzed using two-factor (time and treatment) ANOVA for repeated measurements
Significant main effects located through post-hoc Tukey tests
Sphericity assessed using Mauchley's test of sphericity
One-way ANOVA used to compare time trial performance.

Data Collection Summary:

Timing of Measurements

Before, during and after exercise, blood samples were collected and gas exchange measurements performed.

Dependent Variables

Blood samples analyzed for glucose, insulin, lactate
GI symptoms at rest measured through questionnaire
Gas exchange measurements
Body mass.

Independent Variables

75g glucose dissolved in 500ml water, resting for 15, 45 or 75 minutes before exercising
Subjects asked to record food and activity patterns prior to trial and to follow the same pattern prior to other trials
No strenuous exercise on day before trial
Abstain from alcohol and tobacco for day prior.

Description of Actual Data Sample:

Initial N: Eight subjects, all male
Attrition (final N): Eight
Age: Mean, 28±3 years
Ethnicity: Not mentioned
Location: United Kingdom.

Summary of Results:

Other Findings

There were no differences in performance between conditions as measured by time to completion or mean power produced
There were significant differences in plasma glucose concentration between 15 minutes prior (6.6±0.6mmol per L, P<0.05) and both 45 minutes prior to (4.5±0.2mmol per L) and 75 minutes prior (3.7±0.2mmol per L) immediately before exercise
Insulin concentrations immediately before exercise were higher (P<0.05) during 15 minutes prior (72.6±10.4microU per ml) than during 45 minutes prior (50.8±9.9microU per ml), which was higher (P<0.05) than during 75 minutes prior (33.9±5.5microU per ml). These differences disappeared within 10 minutes of exercise.
Two subjects became hypoglycemic (less than 3.5mmol per L) in the 15 minutes prior to the trial while three and five subjects were transiently hypoglycemic in the 45 minutes prior and 75 minutes prior, respectively
Performance and RPE did not seem to be related to hypoglycemia
There was no interaction between time and condition for mean RER, RPE or heart rate
There were no significant differences between conditions in the reports of severity of GI discomfort.

Author Conclusion:

Altering the timing of the ingestion of carbohydrates before exercise resulted in differences in plasma glucose or insulin responses, which disappeared within 10 minutes of exercise and which had no effect on performance
In conclusion, this study suggests that:

The timing of the ingestion before exercise does not affect subsequent endurance performance within this time frame
Hypoglycemia (below 3.5mmol per Ll) did not seem to affect time trial performance after a 20-minute SS ride.

Funding Source:

University/Hospital:

University of Birmingham

Reviewer Comments:

Inclusion criteria, exclusion criteria and recruitment methods were not well-defined
No power calculations were done
75g may not be enough to have a significant effect.

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?	???
	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?	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?		???
	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