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NAP: Training (2014)

Citation:

Bennett CB, Chilibeck PD, Barss T, Vatanparast H, Vandenberg A, Zello GA. Metabolism and performance during extended high-intensity intermittent exercise after consumption of low- and high-glycaemic index pre-exercise meals. Brit J Nutr. 2012; 108: S81-S90. 

 
Study Design:
Randomized Crossover Trial
Class:
A - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:

To determine the effects of low-GI and high-GI pre-exercise meals on extended high-intensity intermittent exercise performed in a single day. 

Inclusion Criteria:
  • Recreational soccer players
  • Appropriate response to the Physical Activity Readiness questionnaire about health problems that may be exacerbated by exercise
  • Previous participation in competitive soccer or previous cardiovascular training involving running at intermittent intensities
  • Athletic ability to perform two consecutive 90-minute high-intensity intermittent running simulations separated by a three-hour break, identified as a minimum relative peak Vo2 (V02peak) of 45ml and 50ml per kg per minute for females and males, respectively
  • Healthy, non-diabetic, normo-insulinemic response to CHO and exercise. 
Exclusion Criteria:

Non-soccer-playing recreational athletes.

Description of Study Protocol:
Design
  • Randomized and counter-balanced crossover. 
  • Five visits, including the first three to familiarize subjects with the treadmill and meals, then two experimental trials separated by seven days. 
  • Each trial had two 90-minute back-to-back, high-intensity intermittent exercise sessions, separated by three hours. The two sessions were exactly analogous to each other, with each consisting of two 45-minute halves. A 15-minute intermittent treadmill speed protocol was repeated three times to simulate the first 45-minute half of a soccer game. After a 15-minute "half-time" break, participants completed a second 45-minute half comprised of two more 15-minute intermittent treadmill protocols followed by 15 minutes of performance testing. The simulation provides intervals of time at different exercise intensities performed by high-level soccer mid-fielders:
    • 7% standing
    • 56% walking
    • 30% jogging
    • 4% running
    • 3% sprinting.  
  • Part one of Exercise Session One (120 minutes after the test meal): 45-minute simulation (after a five-minute running warm-up on treadmill at 8km per hour followed by three minutes of stretching)
  • 15-minute break
  • Part two of exercise session: A 30-minute simulation, 15 minutes of five one-minute maximal sprints separated by two five-minute rest periods
  • The above is followed by one hour to consume a second test meal. After two hours of rest, a second 90-minute exercise session identical to the first was completed.   

Blinding Used

Single blind.

Intervention

Low-GI meal or an isoenergetic, high-GI meal two hours before each high-intensity intermittent session. The low-GI meal (estimated GIglucose was approximately 36, determined glycemic-responsewhitebread was 46) was comprised of red lentils, Saskatoon berries and liquid honey, which supplied 1.5g per kg body weight of available CHO. The high-GI meal (estimated GIglucose was approximately 76, GIwhitebread was 114) matched for available CHO was instant mashed potato and white bread. A second interim meal of the same composition of the first meal was consumed within one of completing the first session.

Statistical Analysis

A three-factor ANOVA with one between-groups factor for sex and two repeated measures (treatment and time) was used to assess differences in blood glucose and lactate, RER, CHO and fat oxidation, heart rate, expired gases, serum insulin and NEFA, RPE and sprint performance. Baseline levels for blood glucose and lactate between the two treatments were compared using a paired T-test. Outliers were excluded when values fell higher than two SD away from the mean value. Where significance was noted, a least significant difference post-hoc test was used to determine where significant differences existed. 

Data Collection Summary:

Timing of Measurements

Blood at baseline and at 15 minutes, 30 minutes, 60 minutes, 90 minutes and 120 minutes after the meal and at 15 minutes, 45 minutes, 90 minutes and 105 minutes during the exercise session. Gastrointestinal symptoms rating were taken at baseline, 60 minutes and 120 minutes after the meal. Gas samples were taken during the first, third, and fifth 15-minute segments of high-intensity intermittent exercise sessions.

Dependent Variables

  • Blood samples for glucose, insulin, lactate and NEFA
  • CHO and fat oxidation: Expired gases for seven-minute segmnets; V02, Vc02 and RER were measured breath-by-breath using open-circuit indirect calorimetry. Fat oxidation was calculated.
  • Sprint performance: Distance on treadmill 
  • Rating of perceived exertion (RPE): Borg 15-point scale, i.e., six to 20, where six corresponds to very, very easy, and 19 to very, very hard
  • Heart rate: Heart rate monitor
  • Gastrointestinal symptoms rating: Five-point scale with word anchors (zero for no symptoms, four for severe symptoms)
  • Water consumption.

Independent Variables

Low-GI meal or an isoenergetic, high-GI meal.

Control Variables

Subjects completed a detailed 48-hour activity and dietary intake record before the first trial day and duplicated both for the second trial day. Subjects abstained from strenuous activity during the 24-hour before a trial. No foods other than the provided foods during the trials. Water ad libitum throughout the first trial and intake as duplicated for a second trial day. 

Description of Actual Data Sample:
  • Initial N: 22 (13 males, nine females)
  • Attrition (final N): 14 (10 males, four females).
Age
  • Males: 27.2±8 years
  • Females: 22.5±4.4 years.

Other Relevant Demographics

  • V02max:
    • Males: 55.8ml per kg per minute
    • Females: 54.6±4.8ml per kg per minute.
  • HRmax: 
    • Males: 191±16bpm
    • Females: 191±13bpm.
  • Maximum treadmill velocity (Vmax):
    • Males: 17.0±1.9km per hour
    • Females: 16.3±1.0km per hour.

Anthropometrics

BMI: 

  • Males: 22.2±1.6
  • Females: 21.9 ± 1.8.

Location

Canada.

 

Summary of Results:

Findings

  • With the exception of NEFA, no significant sex x treatment or sex x treatment x time interaction were found, so all analyses combined the men and women
  • Blood glucose showed a treatment x time interaction (P<0.001). Post hoc analysis showed that blood glucose was significantly higher in the high-GI meal compared with low-GI during the post-prandial period at 30 minutes, 60 minutes and 90 minutes. Blood glucose was significantly higher during the low-GI compared with high-GI at 375 minutes near the end of the second high-intensity intermittent exercise session, just before the second set of sprints. 
  • A treatment x time interaction for serum insulin was evident (P=0.003, N=9). Insulin levels for the high-GI were significantly higher than low-GI before beginning the first high-intensity intermittent exercise session (post hoc analysis; P=0.001).
  • A treatment x time interaction for lactate was noted (P=0.019, N=12). Post hoc analysis showed that low-GI elicited a significantly higher lactate response than the high-GI meal during the post-prandial period at 30 minutes and 60 minutes. In contrast, lactate was higher near the end of the second high-intensity intermittent exercise session, before the second set of sprints (at 375 minutes) for the high-GI meal. 
  • A sex x treatment x time interaction (P=0.025) existed for NEFA. For the last time point, females on high-GI had higher NEFA than on low-GI (P<0.001)
  • There was a treatment x time interaction for CHO oxidation (P=0.039). High-GI elicited a significantly higher CHO oxidation from three minutes to 10 minutes of the first high-intensity intermittent exercise session
  • Fat oxidation rates increased over time during both trial days (P<0.001, N=12) with no difference between high- and low-GI conditions
  • No treatment x time interaction was apparent for RER in the trials (P=0.28). The RER did decrease over time in both trials (P<0.001)
  • Sprint performance at the end of each high-intensity intermittent exercise session was not significantly affected by the GI of the pre-exercise test meal. A main effect for time (P<0.001) was observed at the end of the second exercise session, with the distance covered during the third, fourth and fifth sprints lower than for the other sprints. 
  • RPE showed a significant time main effect, increasing over time during both high-intensity intermittent exercise sessions (P<0.001). RPE was not influenced by the meal GI (P=0.867)
  • There were no significant differences in heart rate between trials or over time
  • After meal consumption, perceived hunger was significantly lower during low-GI compared to high-GI (P<0.001). Ratings of fullness were significantly higher during low-GI vs. high-GI (P<0.001). Adverse symptoms of bloating, nausea and abdominal cramps were not significantly different over or between treatments. 
  • An average of 4,000ml of water were consumed during exercise on each trial day. 
Author Conclusion:

Extended high-intensity intermittent exercise metabolism was altered to a small extent by changes to the GI of pre-exercise meals, although changes in performance were not seen. Metabolic changes with low-GI meals included increased blood glucose and decreased lactate production late in exercise, and reduced insulin and CHO oxidation at the beginning of a simulated soccer tournament. 

Funding Source:
Government: Natural Science and Engineering Research Council of Canada
Not-for-profit
Saskatchewan Health Research Foundation
Other non-profit:
Other: Saskatchewan Pulse Growers
Reviewer Comments:
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? 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) 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? N/A
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? N/A
  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.) N/A
  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? 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? N/A
  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? N/A
  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? N/A
  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