EAL

NAP: Competition (2007)

Citation:

Jentjens RLPG, Cale C, Gutch C, Jeukendrup AE. Effects of pre-exercise ingestion of differing amounts of carbohydrate on subsequent metabolism and cycling performance. Eur J Appl Physiol. 2003; 88: 444-452.

PubMed ID: 12527976

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 effects of ingesting differing amounts of glucose pre-exercise on glucose and insulin responses during exercise and on time-trial cycling performance.

Inclusion Criteria:

Well-trained male cyclists or triathletes, assessed as healthy from a general health questionnaire.

Exclusion Criteria:

None specifically mentioned.

Description of Study Protocol:

Recruitment: Methods not described.
Design: Randomized crossover trial
Blinding used: Single-blind; lab tests.

Intervention

Subjects completed four exercise trials separated by at least three days
At 45 minutes before the start of exercise, subjects consumed 500ml of a beverage containing 0g (placebo), 25g (low), 75g (medium) or 200g (high) of glucose
Exercise trials consisted of 20 minutes of submaximal steady-state exercise at 65% of maximal power output, followed by a 691±12kJ time trial.

Statistical Analysis

Data from four trials compared using two-factor (time and treatment) ANOVA for repeated measurements
Greenhouse-Geisser correction was used to adjust the significance level of the test statistics for violation of sphericity
Tukey post-hoc tests used when ANOVA revealed a significant interaction
One-way ANOVA for repeated measurements used to compare time trial performances.

Data Collection Summary:

Timing of Measurements

Blood samples taken before exercise and every five minutes during exercise
RPE also measured every five minutes
Gas exchange measurements and heart rate measured throughout exercise.

Dependent Variables

Weight, height, body composition through skinfolds
Heart rate recorded using radio telemetry
Gas exchange measurements made using automated gas analysis system
RPE using Borg category scale
Blood samples analyzed for glucose, lactate and insulin.

Independent Variables

500ml of a beverage containing 0g (placebo), 25g (low), 75g (medium) or 200g (high) of glucose
Subjects asked to record food and activity intakes during day before first trial and repeat the pattern before other trials
Avoid vigorous exercise and abstain from drinking alcohol and tobacco for 24 hours prior to testing.

Description of Actual Data Sample:

Initial N: Nine male cyclists
Attrition (final N): Nine
Age: Mean, 29.6±2.4 years
Ethnicity: Not mentioned
Location: United Kingdom.

Summary of Results:

	Time Trial (Minutes)	Average Exercise Intensity (W)	Average HR (Beats per Minute)	Maximal Heart Rate Percentage
Placebo	42:34±0:48	271±6	171±5	92±2
Low	43:21±0:19	267±10	168±8	91±3
Medium	43:07±1:04	268±8	171±3	92±2
High	42:12±0:42	271±7	168±6	91±2

Other Findings

Plasma insulin concentrations at the onset of exercise were significantly higher (P<0.05) in the medium and high levels, compared with low and placebo.
Plasma glucose concentration fell rapidly (P<0.05) during steady-state exercise in all glucose trials, but remained steady in placebo
No difference in plasma glucose concentrations was observed between the glucose trials at any time
Hypoglycemia (less than 3.5mmol per L) was observed in six subjects during steady state, but only after ingesting glucose pre-exercise
However, there was no difference in time trial performance, heart rate or RPE between the four trials.

Author Conclusion:

In conclusion, ingestion of 25g, 75g or 200g of glucose 45 minutes before 20 minutes of exercise does not affect performance in a subsequent 40-minute time trial, compared with a placebo
In addition, rebound hypoglycemia following pre-exercise glucose ingestion does not negatively affect performance.

Funding Source:

Not-for-profit

Foundation associated with industry:

Reviewer Comments:

Inclusion criteria, exclusion criteria and recruitment methods 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?		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?		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?	N/A
	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?	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