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NAP: Competition (2007)

Citation:
Diboll, DC, Boone WT, Lindsey LR. Cardiovascular and metabolic responses during 30 minutes of treadmill exercise shortly after consuming a small, high-carbohydrate meal. Int J Sports Med. 1999; 20: 384-389. PubMed ID: 10496118
 
Study Design:
Randomized crossover trial
Class:
A - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:
The aim was to determine whether a small, high-carbohydrate meal consumed just prior to exercise would alter cardiovascular and metabolic responses in these endurance-trained individuals during 30 minutes of treadmill exercise at moderate intensity.
Inclusion Criteria:
The subjects were highly-trained competitive triathletes or distance runners with VO2 peaks at 64.8 (±8.7ml x kg -1 x min -1).
Exclusion Criteria:
No specific exclusion criteria were stated. 
Description of Study Protocol:
  • Recruitment: Authors did not specify how or where subjects were obtained.
  • Design
  • Clinical trial with crossover protocol
  • All subjects participated alternately in the control or intervention group in the crossover design, with minimal washout period (two days) between initial crossover protocols
  • Initial assignment to control or intervention group was randomized.

Blinding Used

No blinding was used athough authors state that subjects were given minimal informtion about the study's aim. 

Intervention (if applicable)

  • Subjects fasted 12 hours (water was allowed) prior to testing
  • Additionally, subjects did not participate in strenuous physical activities 24 hhours prior testing
  • The intervention meal contained 2,088kJ, 91.5g carbohydrate (77% of energy content), 14g protein (16% of energy content) and 3.6g fat (7% of energy content)
  • The order of CHO-M and FAST was randomized
  • Intervention subjects were instructed to eat the meal within 10 minutes and rest five minutes before exercise on a treadmill for 30 minutes at a pre-determined speed intended to represent 65% of VO2peak, based upon results of a graded treadmill test conducted several days before testing to directly measure VO2 consumption in each individual.
Statistical Analysis
  • 2 x 3 (treatment x time) analysis of variance (ANOVA) with repeated measures
  • Follow-up analyses to ANOVA for the purpose of determining where significant differences occurred in the time main effect were performed using Dunn-Sidak adjusted tests
  • The two levels for the treatment main effect were collapsed into one to perform these post-hoc analyses.
Data Collection Summary:

Timing of Measurements

Measurements were taken:

  1. Prior to the trial to determine 65% of VO2peak for each subject
  2. Five different periods in each of the two trial periods:
    • Last five minutes of initial pre-workout 15-minute rest
    • Last five minutes of post-prandial (intervention group) or additional rest (control group) period prior to workout
    • Last five minutes of each of three 10-minute workout segments, but two of the measures (cardiac output and stroke volume) were taken in the last minute of each 10-minute segment. Heart rate was done with rhythm strip calculations at the end of every minute of the five-minute data collection periods.

Dependent Variables

  • Heart rate measured by Nihon Kohden LifeScope 6
  • Stroke volume was measured by dividing cardiac output by heaert rate
  • Cardiac output measured by SensorMedics MMC with Collier plateau breathing procedure and Fick equation
  • VO2 measured by SensorMedics MMC with expired breath
  • Respiratory Exchange ratio (RER) measured by SensorMedics MMC with expired breath
  • Volume of CO2 measured by SensorMedics MMC with expired breath.

Independent Variables

Fasting or consumption of small high-CHO meal 15 minutes prior to running for 30 minutes.

Control Variables

Baseline VO2peak and RER.
Description of Actual Data Sample:
  • Initial N: 14 males
  • Attrition (final N): 13 males for heart rate and stroke volume measures; 14 males for other measures
  • Age: 25±6 years
  • Ethnicity: Not specified
  • Location: Mississippi.

 

Summary of Results:

Other Findings

  • Statistical analyses indicated that the carbohydrate meal did not affect heart rate, stroke volume, cardiac output, VO2 or respiratory exchange ratio, compared to the fasting condition
  • While there were no differences in control and intervention groups, three variables increased significantly across time for all subjects: Heart rate (P<0.001); stroke volume (P<0.001); cardiac output (P=0.0018)
  • While pre-trial workouts measured 65% VO2peak, actual trials showed subjects were exercising at 58%±5% for the meal session and 55±5% for the fasting sesssion.
Author Conclusion:
  • In summary, our data indicate that a small high-carbohydrate meal consumed shortly before 30 minutes of moderate-intensity treadmill exercise did not significantly alter cardiovascular function, specifically heart rate, stroke volume and cardiac output
  • Also contrary to published data concerning larger meals, VO2 was not significantly different between our exercise conditions, which suggests that the meal did not induce an additional exercise energy expenditure
  • Thus, these results suggest that consuming small amounts of carbohydrates prior to endurance exercise will not alter exercise cardiovascular function and will not influence overall energy expenditure during moderate-intensity exercise.
Funding Source:
University/Hospital: University of Southern Mississippi
Reviewer Comments:
  • Authors did not standardize meal to body size
  • Authors did not specify the fiber content of the carbohydrate meal, but rather counted total carbohydrates
  • Inclusion criteria, exclusion criteria and recruitment methods were not described
  • No power calculations were done. 
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? 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? 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? No
  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? 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? ???
  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? ???
  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)? ???
  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? No
  10.2. Was the study free from apparent conflict of interest? Yes