EAL

NAP: Competition (2007)

Citation:

Cramp T, Broad E, Martin D, Meyer BJ. Effects of preexercise carbohydrate ingestion on mountain bike performance. Med Sci Sports Exerc. 2004; 36 (9): 1,602-1,609.

PubMed ID: 15354044

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 the performance and metabolic effects of consuming 1.0g and 3.0g carbohydrate per kg body mass, three hours before a 93-minute simulated mountain bike race.

Inclusion Criteria:

Trained male mountain bike cyclists who competed in club-level races on a regular basis and were in either a general preparation and maintenance phase or endurance phase of training for the upcoming season, more than eight hours of training on the bike per week.

Exclusion Criteria:

None specifically mentioned.

Description of Study Protocol:

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

Intervention

1.0g and 3.0g carbohydrate per kg body mass, three hours before a 93-minute simulated mountain bike race
The high-CHO meal was supplemented with maltodextrin, while maintaining the same glycemic index and apparent volume of the low CHO meal.

Statistical Analysis

Data analyzed in complete random block design using two-way and three-way ANOVA with repeated measures
Post-hoc Newman-Keuls test and critical ranges was used to determine the level of statistical significance between means and at specific times
Correlation matrices were used to assess whether there was any relationship between variables.

Data Collection Summary:

Timing of Measurements

Subjects underwent two trials on a cycle ergometer after test meals consumed three hours prior
RER and VO₂ measured during exercise, blood samples collected every 30 min for two hours after meal consumption and during exercise.

Dependent Variables

Athletic performance measured as the total work performed on a cycle ergometer in six 30-second periods each lap during the test
Body mass measured using digital scale
Body fat determined through skinfold testing
RER and VO₂ measured through Douglas bag system
Blood samples analyzed for FFA, insulin
Gastric comfort measured on a scale from one to five
RPE measured using Borg scale.

Independent Variables

1.0g or 3.0g CHO per kg test meals three hours prior to exercise, equivalent in volume
Subjects were given food and activity diaries to record intake and activity for the previous 48 hours
Subjects asked not to consume any alcohol or caffeine in 24 hours prior to trial.

Description of Actual Data Sample:

Initial N: Eight male subjects
Attrition (final N): Eight
Age: Mean, 22±6.3 years
Ethnicity: Not mentioned
Location: Australia.

Summary of Results:

Other Findings

Performance in Lap One was better with low-CHO (12.0±2.2kJ vs. 11.3±1.9kJ, P=0.03), whereas performance in Lap Four was better for high-CHO (12.2±1.5kJ vs. 10.7±2.1kJ, P=0.02)
Overall performance was 3% greater in high-CHO, compared with low-CHO (NS, P=0.13), equating to a two-minute 48-second time advantage
Serum glucose was significantly lower (P<0.04) in high-CHO immediately before the mountain bike test (180 minutes post-prandial) and at 10 minutes into the test (P<0.01)
Insulin level peaked 30 minutes post-prandial in both trials, but the response was greater in the high-CHO from 30 minutes until 120 minutes (P=0.01)
There was no difference in the FFA response to different quantities of CHO ingestion
GI comfort decreased similarly for both trials over time (P<0.05)
There was no significant difference for average daily nutrient intake.

Author Conclusion:

In summary, this study has shown that a high-CHO (three grams per kg) pre-exercise meal has a potentially greater benefit to performance than a smaller meal taken three hours before intermittently intense endurance exercise (over 90 minutes)
The mechanism for overall improved performance appears to be attributable to a greater CHO oxidation rate due to increased CHO availability from serum glucose
The temporary decline in performance early during exercise in the high-CHO trial was probably a result of low serum glucose and raised insulin levels immediately before and early during exercise. However, these results have raised the question of whether the physiologic changes may have promoted a pacing strategy thus contributing to potential performance benefits.
Further research is warranted to investigate whether a high-carbohydrate meal can benefit performance over true mountain bike race distances.

Funding Source:

Government:	Australian Institute of Sport
University/Hospital:	University of Wollongon

Reviewer Comments:

Inclusion criteria, exclusion criteria and recruitment methods not described
Small sample size; no power calculations done
Authors note that since subjects had adequate nutrition in days before testing, CHO stores were sufficient to last through the test for both groups.

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