EAL

NAP: Training (2014)

Citation:

Currell K and Jeukendrup A. Superior endurance performance with ingestion of multiple transportable carbohydrates. Med Sci Sports Exerc. 2008 (40) 2,275-2,281.

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 effects of ingesting a glucose and fructose beverage compared with a glucose beverage and a water placebo on endurance cycling performance.

Inclusion Criteria:

Male
Trained cyclist.

Exclusion Criteria:

Not discussed.

Description of Study Protocol:

Recruitment

Not discussed.

Design

Subjects first undertook an incremental exercise test on braked cycle ergometer to determine maximum oxygen uptake (VO_2max) and maximum power output (Wmax)
One to two weeks following initial assessment, subjects completed three experimental trials in random order. Prior to start of training session, subjects consumed 600ml bolus of test beverage.
Each trial was on a cycle ergometer and the subject worked until perceived exhaustion, starting with 95W and increasing by 35W every three minutes. Subjects continued to drink 150ml of the test beverage every 15 minutes of the steady-state period and at 25%, 50% and 75% of the time trial.

Blood samples measured plasma glucose and lactate
Gas analysis measured VO₂ and carbon dioxide production (VCO₂)
Heart rate was measured by radiotelemetry heart rate monitor
Rate of perceived exertion (RPE) was assesed every 15 minutes using Borg 6-20 scale.

Blinding Used

Not discussed.

Intervention

Ingestion of glucose or glucose-fructose mixture consumed during physical activity on performance endurance as compared to water placebo.

Statistical Analysis

Two-way ANOVA for mean power output from the time trials and expired air data
Two-factor ANOVA with repeated measures for blood glucose and lactate, heart rate, cadence and RPE
In case of significance, post-hoc analysis was undertaken with Tukey's HSD to locate the difference
Significance was set at the P<0.05 level.

Data Collection Summary:

Timing of Measurements

Experiments took place in the morning one to two weeks apart.

Dependent Variables

Maximum oxygen uptake: VO_2max
Maximum power output.

Independent Variables

Type of carbohydrate (14.4% CHO concentration): Glucose or glucose+fructose, as compared to water placebo fed at a rate of 1.8g per minute.

Control Variables

All participants were trained male cyclists.

Description of Actual Data Sample:

Initial N: Eight males
Attrition (final N): Eight males
Age: 32±7 years
Ethnicity: Not discussed
Anthropometrics
- Weight: 84.4±6.9kg
- VO_2max: 64.7±3.9ml*kg^-1*min^-1
- W_max: 364±31.
Location: Birmingham, United Kingdom.

Summary of Results:

Key Findings

Variables	Water Control Trial (Placebo)	Glucose Experimental Trial	Glucose+Fructose Experimental Trial	Statistical Significance of Group Difference
VO₂	2.94±0.18	2.91±0.21	2.93±0.21	N/A
Mean Power	231±9W	254 ± 8 W	275±10
CHOtot (g·min^-1)	2.03±0.24	2.03±0.24^a	2.54±0.25^a
FATtot (g·min^-1)	0.65±0.07	0.44±0.08^a	0.44±0.08^a

a: Significantly different from W.

Other Findings

Average power output between 25% and 50% of the target work during the time trial was significantly greater in GF and both G and P
There was no difference in the VO₂ between the three trials
Ingestion of GF led to significantly higher plasma lactate concentrations, compared to both G and W after 15 minutes of exercise
There was no difference between any of the trials for heart rate, cadence or RPE
Plasma glucose was significantly greater from 15 minutes after exercise in GF and G compared with W in two-hour steady state period
CHO oxidation was significantly greater in both CHO trials vs. placebo (P<0.05) and fat oxidation was lower, but there was no difference between GF and glucose.

Author Conclusion:

This is the first study to show clear performance benefits of glucose plus fructose over and above the effects of glucose alone
These findings suggest that increased exogenous carbohydrate oxidation can be linked to increased performance; glucose was oxidized at a higher rate than fructose.

Funding Source:

Industry:

GlaxoSmithKline

Pharmaceutical/Dietary Supplement Company:

Reviewer Comments:

Sample size of eight is small
No mention if subjects did or did not perform exercise prior to testing days
No mention if subjects did or did not consume breakfast prior to coming to lab on testing days
Probably not blinded (this was not discussed): It is possible that subjects and researchers were blinded as to glucose vs. glucose+fructose, but unless water was sweetened with non-caloric sweetener, placebo was not blinded
Recruiting not discussed.

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)	N/A
	2.	Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about?	N/A
	3.	Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice?	N/A
	4.	Is the intervention or procedure feasible? (NA for some epidemiological studies)	N/A

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?	No
2.	Was the selection of study subjects/patients free from bias?		No
	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?	No
	2.3.	Were health, demographics, and other characteristics of subjects described?	No
	2.4.	Were the subjects/patients a representative sample of the relevant population?	No
3.	Were study groups comparable?		N/A
	3.1.	Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT)	N/A
	3.2.	Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline?	N/A
	3.3.	Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.)	N/A
	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")?	???
4.	Was method of handling withdrawals described?		N/A
	4.1.	Were follow-up methods described and the same for all groups?	N/A
	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%.)	N/A
	4.3.	Were all enrolled subjects/patients (in the original sample) accounted for?	N/A
	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?		???
	5.1.	In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate?	???
	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?	???
	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?	N/A
	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?	No
	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?	No
	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