EAL

NAP: Training (2014)

Citation:

Jeukendrup AE, Moseley L, Mainwaring GI, Samuels S, Perry S, Mann CH. Exogenous carbohydrate oxidation during ultraendurance exercise. J Appl Physiol. 2006; 100: 1,134-1,141.

PubMed ID: 16322366

Study Design:

Non-Randomized Crossover Trial

Class:

C - Click here for explanation of classification scheme.

Quality Rating:

NEUTRAL: See Quality Criteria Checklist below.

Research Purpose:

To obtain a measure of exogenous carbohydrate oxidation and plasma glucose kinetics during five hours of exercise
To compare exogenous carbohydrate following the ingestion of a glucose solution or a glucose + fructose solution during ultra-endurance exercise.

Inclusion Criteria:

Endurance-trained men who have Ironman distance triathlon personal best times of less than 10 hours, 30 minutes or hold an elite road racing license (national level)
Signed a consent form.

Exclusion Criteria:

Not reported.

Description of Study Protocol:

Recruitment

The subjects volunteered to participate in the study. Recruitment was not otherwise described.

Design

Subjects visited the laboratory on four different occasions, once for preliminary testing and three times for experimental trials
Preliminary testing was was conducted one week before the start of the experiment to determine maximal work rate. Subjects were asked to perform a graded exercise test to exhaustion on an electromagnetically braked cycle ergometer. Subjects started cycling at 95 W, and the work rate was increased by 35 W every three minutes until exhaustion.
For the experimental trials, subjects commenced exercising at 50% of their previously determined maximal work rate. At the onset of exercise, a [6,6-²H]glucose prime was given. Thereafter, a continuous sterile, pyrogen-free infusion of [6,6-²H]glucose dissolved in isotonic saline was administered at a rate of ~0.7µM per kg^-1 per minute^-1. At the onset of exercise, subjects consumed an initial bolus of 600ml of beverage followed by 270ml at 20-minute intervals throughout the trial.

Blinding Used

Subjects were blinded to the beverage composition given during exercise.

Intervention

During the trial, subjects ingested a beverage of either glucose, glucose + fructose (2:1) or water. The CHO beverages delivered 1.5g per minute CHO and consisted of either 100% glucose or 2:1 ratio of glucose + fructose. Both CHO beverages had a naturally high abundance of ¹³C. The glucose beverage had an osmolality of 665±3mosmol per kg H₂O and the glucose + fructose beverage had an osmolality of 659±3mosmol per kg H₂O. The water beverage had an osmolality of 11±1mosmol per kg H₂0. All three drinks contained 30mmol per L of sodium in the form of sodium citrate.

Statistical Analysis

Data for fullness, RPE, HR and cadence were averaged for each hour. Data were checked to ensure that parametric assumptions were met, and a two-way (time x trial) ANOVA for repeated measures was applied. All data were checked for sphericity, and, where necessary, a Huynh-Feldt correction was used. In all cases, a Tukey honestly significant difference test was applied in the event of a significant F-ratio. Statistical significance was set a P<0.05.

Data Collection Summary:

Timing of Measurements

During experimental trials, blood and breath samples were taken every 20 minutes, as were measures of gastrointestinal fullness and ratings of perceived exertion (RPE). Heart rate was continuously recorded at 15-second intervals and averaged over each hour.

Dependent Variables

Lactate concentrations: Determined enzymatically via blood analysis
Glucose concentrations: Determined enzymatically via blood analysis
Glycerol concentrations: Determined enzymatically via blood analysis
Triglyceride concentrations: Determined enzymatically via blood analysis
Free fatty acid concentrations: Determined enzymatically via blood analysis
[²H]glucose enrichment: Determined via blood analysis
¹³C enrichment: Via breath analysis of expired air
Total fat oxidation rates: Calculated using indirect calorimetry and breath enrichment
Total carbohydrate oxidation rates: Calculated using indirect calorimetry and breath enrichment
Exogenous carbohydrate oxidation rates: Calculated using indirect calorimetry and breath enrichment
Endogenous carbohydrate oxidation rates: Calculated using indirect calorimetry and breath enrichment
Gastrointestinal fullness: Measured using a 10-point scale
Ratings of perceived exertion: Measured using the 6-20 point scale of Borg
Heart rate: Continuously recorded at 15-second intervals and averaged over each hour.

Independent Variables

Composition of beverage consumed during exercise:

Glucose
Glucose + fructose
Water.

Control Variables

Timing of measurements
Rate of beverage ingestion
Standardized exercise protocol.

Description of Actual Data Sample:

Initial N: Eight males
Attrition (final N): Eight
Age: Mean, 30 years (SE, four years).

Other relevant demographics (Mean±SE):

Peak power output (W_max): 367±6 W
Maximum O₂ update (VO_2max): 4.69±0.16L per minute
VO_2max per kg: 62.7±2.3ml per kg^-1 per minute^-1.

Anthropometrics (Mean±SE):

Height: 1.78±0.02m
Body weight: 75.3±3.2kg.

Location

Birmingham, UK.

Summary of Results:

Key Findings

Ingestion of water resulted in significant increases in fat oxidation and decreases in total CHO oxidation over time (P<0.05)
The ingestion of both CHO beverages resulted in a rapid and significant rise in d¹³CO₂(p<0.05); there was no significant changes in ¹³CO₂production following the ingestion of water (grand mean = -25.4±0.1)
Breath d¹³CO₂ enrichment was significantly different between CHO trials at 20 minutes to 140 minutes, 220 minutes, 260 minutes and 300 minutes (P<0.05)
CHO_EXO rates in glucose + fructose leveled off earlier than glucose (100 minutes vs. 120 minutes, P<0.05). Glucose + fructose had greater CHO_EXOat 20 minutes to 120 minutes, 220 minutes and 300 minutes (P<0.05) and exhibited a greater mean CHO_EXO once the oxidation rate leveled off (glucose was 1.32±0.04g per minute, glucose+fructose was 1.49±0.06g per minute). These differences resulted in a significant difference between the estimated total amounts of CHO_EXO oxidized during the exercise period. A minimum of 293±9g was oxidized in glucose and a minimum of 346±9g was oxidized in glucose+fructose.
The ingestion of CHO resulted in an increase in the rate of appearance (R_a) of glucose (P<0.05). The pattern of the increase over time was similar in both CHO trials, linear in nature with a peak at 300 minutes of exercise (glucose was 144±18, glucose + fructose was 137±30mmol per kg^-1 per minute^-1.) The ingestion of water resulted in no increase in glucose R_a over time; R_a at exhaustion was lower than either of the CHO trials (46±6mmol per kg^-1 per minute^-1).
The ingestion of CHO also resulted in a linear increase in the rate of disappearance (R_d) of glucose, with a maximum occurring at 300 minutes (glucose was 144±8mmol, glucose + fructose was 137±30mmol per kg^-1 per minute^-1).
The ingestion of CHO resulted in a transient but significant increase in plasma glucose concentration (P<0.05). At 20 minutes, plasma glucose concentrations in glucose and glucose + fructose were 6.2±0.34mmol and 6.04±0.11mmol per kg^-1 per minute^-1,respectively, compared with 4.70±0.06mmol per L in water).The ingestion of water resulted in a steady decline in plasma glucose concentration, with the nadir occurring at fatigue (3.44±0.14mmol per L).
Plasma lactate at rest was similar in all trials (0.83±0.09mmol per L). The ingestion of glucose + fructose caused a transient elevation in plasma lactate, such that it was higher than in glucose at 40 minutes (1.84±0.16 vs. 1.27±0.09mmol per L) and higher than in water at 20 minutes, 40 minutes and 80 minutes (P<0.05). In water, plasma lactate rose gradually over time and was greater at exhaustion than at zero minutes (1.53±0.13mmol vs. 0.81±0.09mmol per L).
The ingestion of water resulted in an increase in plasma free glycerol concentration, to levels significantly higher (P<0.05) than those occurring in glucose and glucose = fructose (0.47±0.03mmol, 0.18±0.01mmol and 0.17±0.03mmol per L at exhaustion for water, glucose and glucose + fructose, respectively)
The ingestion of water resulted in an increase in plasma free glycerol concentration (from 241±70mmol to 1,573±133mmol per L), to levels significantly higher (P<0.05) than those occurring in glucose and glucose + fructose in latter stages of exercise (1,571±133mmol, 655±55mmol and 583±73mmol per L, respectively, at exhaustion)
There was no effect of drink composition on plasma-free triglyceride concentrations.

Other Findings

Heart rate rose over time in all trials but was lower in water than in both CHO trials in the first hour (115±3 vs. 125±3 and 124±3 beats per minute, respectively) and lower than glucose in the third hour (123±3 vs. 133±3 beats per minute)
Only with the ingestion of glucose + fructose were subjects able to maintain cadence (92±3rpm in the first hour and 87±2rpm in the final hour); a fallover time occurred in both water and glucose (from 88±2 and 89±2rpm to 81±3 and 78±2rpm, respectively)
There was a gradual and significant rise in RPE over time in all trials. There was a trend in the final hour of exercise for RPE to be lower following the ingestion of glucose + fructose (13.1±0.7) compared with water (14.2±0.7) or glucose (14.2±0.8)
There was a significant increase in ratings of perceived fullness in glucose over time (first hour, 4.0± 0.6; final hour, 5.7±0.5), resulting in a significant difference (P<0.05) between glucose and both water and glucose + fructose in the final hour of exercise.

Author Conclusion:

Even when CHO is ingested at high rates, gluconeogenesis may play an important role after three hours of exercise. Ingestion of a solution containing both glucose and fructose (2:1 ratio) resulted in an increase in exogenous CHO compared with the glucose solution, even after five hours of exercise, suggesting exogenous CHO occurring in the liver and formation and oxidation of non-glucose energy substrates during exercise.

Funding Source:

Other:

Not reported

Reviewer Comments:

Small study; only eight subjects
All study subjects were men
Procedure for blood and breath analysis was well described
Were subjects randomized to beverage group?
Was adherence to pre-experiment protocol monitored?
Funding source was not described.

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?		N/A
	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?	Yes
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)	No
	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?	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?	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?		N/A
	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?		No
	10.1.	Were sources of funding and investigators' affiliations described?	No
	10.2.	Was the study free from apparent conflict of interest?	N/A