EAL

NAP: Competition (2007)

Citation:

Meyer T, Gabriel HHW, Auracher M, Scharhag J, Kindermann W. Metabolic profile of 4 h cycling in the field with varying amounts of carbohydrate supply. Eur J Appl Physiol. 2003; 88: 431-437.

PubMed ID: 12527974

Study Design:

Randomized crossover trial

Class:

A - Click here for explanation of classification scheme.

Quality Rating:

POSITIVE: See Quality Criteria Checklist below.

Research Purpose:

To describe and reinvestigate metabolic and cardiovascular reactions to long-term steady-state endurance training under conditions of varying CHO supplementation.

Inclusion Criteria:

Endurance-trained male competitive cyclists and triathletes, all accustomed to training sessions of several hours' duration
Individual anaerobic threshold had to exceed 3.0W per kg.

Exclusion Criteria:

Medical history, physical examination, echocardiography and determination of laboratory parameters checked for health risks and acute and chronic inflammatory diseases, which would have excluded participation.

Description of Study Protocol:

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

Intervention

Subjects performed three four-hour endurance rides on their own bicycles with simultaneous spiroergometry: Constant workload 70% individual anaerobic threshold as monitored by SRM-System
Before and during exercise, subjects were administered a total volume of 50ml per kg of 0%, 6% or 12% carbohydrate
All tests were performed within four weeks with only two days between trials.

Statistical Analysis

Differences between constant-load trials tested by two-factor ANOVA (concentration x time)
Post-hoc testing was performed using the Scheffe test.

Data Collection Summary:

Timing of Measurements

Performance was measured during the trial
Blood samples were taken at the end of each state and one, three, five and 10 minutes after exercise
Spiroergometry was carried out during the stage test
Heart rate was measured continuously.

Dependent Variables

Performance was measured through the time trial
Blood samples were analyzed for lactate, glucose, FFA and glycerol
Gas exchange was measured through spiroergometry
Heart rate was measured using a telemetric system.

Independent Variables

Before and during exercise, subjects were administered a total volume of 50ml per kg of 0%, 6% or 12% carbohydrate
Subjects were not permitted to change training routine; no strenuous exercise for two days prior to trials
Nutrition was kept similar on the day prior to trials, verified by analysis of nutritional protocols.

Description of Actual Data Sample:

Initial N: 14 male subjects
Attrition (final N): 14
Age: Mean, 25±5 years
Ethnicity: Not mentioned
Location: Germany.

Summary of Results:

	Mean (SD)	Range
P_max (W)	366±41	275-450
HR_max	189±9	176-203
Lactate (mmol/l)	10.5±2.4	5.8-15.0
P - IAT (W)	269±30	215-315
70% IAT (W)	189±21	150.5-220.5

Other Findings

After cessation of exercise, significant differences between 0% and both carbohydrate concentrations were detected for blood glucose (75mg/dL for 0% vs. 101mg/dL for 6% vs. 115mg/dL for 12%; P<0.0001) and respiratory exchange ratio (0.84 vs. 0.88 vs. 0.90; P<0.01; correlation to glucose, R=0.46; P<0.05).
Free fatty acids (0.19 vs. 0.16 vs. 0.10mmol/l) and glycerol (0.41 vs. 0.22 vs. 0.12mmol/l) were significantly different between endurance trials in a dose-dependent manner (P<0.0001)
Lactate concentration (P=0.42) and heart rate (P=0.12) had no significant influence from carbohydrate substitution.

Author Conclusion:

In conclusion, we have shown that carbohydrate supplementation during cycling sessions of four hours' duration leads to inhibited lipolysis and enhanced reliance on glucose metabolism in a dose-dependent manner. This might be advantageous for the maintenance of high-power outputs during training and competition.
Under field conditions, results from laboratory investigations could be replicated, and thus validated.

Funding Source:

Not-for-profit

Foundation associated with industry:

Reviewer Comments:

Authors note that muscle biopsies were not performed, so muscle glycogen levels two days between trials may have had an influence. However, trials were completed in random order.

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?		Yes
	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?	Yes
	2.2.	Were criteria applied equally to all study groups?	Yes
	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?	Yes
	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?	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?	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