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NAP: Training (2014)

Citation:

 Moore LJS, Midgley AW, Vince R, McNaughton LR. The effects of low and high glycemic index 24-h recovery diets on cycling time trial performance. J Sports Med Phys Fitness. 2011; 51: 233-240.

 
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:

To examine the effect of high-recovery carbohydrate meals with different glycemic index (GI) values on endurance performance, more specifically time trial cycling performance.

Inclusion Criteria:
  • Cycled five or more times per week
  • Free from illness or injury
  • Taking no medication that may affect their exercise response.
Exclusion Criteria:

Not reported.

Description of Study Protocol:
Design

In this randomized, crossover trial, 10 male cyclists performed two 40km time trials separated by at least seven days. Seven to 10 days prior to the trial maximum oxygen consumption (VO2max) and maximum heart rate (HRmax) were determined. Subjects followed the same diet and training schedule during the two days prior to each trial, which was verified by food and training analysis, and had no strenuous exercise, caffeine or alcohol in the 24 hours before each trial. On day one subjects had baseline measures taken (blood sample and expired air sample) and a heart rate monitor attached. After a five-minute warm-up, subjects completed a glycogen-depleting protocol, riding an ergometer for two hours at 75% maximum heart rate, then four 30-second sprints separated by two minutes of passive recovery. Subjects then received one of two different recovery diets [low glycemic index (LGI) or high glycemic index (HGI)] 30 minutes after the completion of the glycogen-depleting protocol, starting with breakfast provided at the lab, and were asked to follow a prescribed 24-hour meal plan. On day two subjects returned to the lab two to three hours post-prandial and completed a 40km time trial. After at least a seven-day washout period, subjects repeated the glycogen-depleting protocol, recovery diet and 40km time trial. 

Blinding Used

Single-blinded study.

Intervention

  • All subjects were provided isocaloric breakfast meals in the lab [low glycemic index (LGI) or high glycemic index (HGI)] 30 minutes after the completion of the glycogen-depleting protocol. Subjects were then asked to follow either a LGI or HGI 24-hour meal plan. Per prescribed meal plan, subjects were asked to eat:
    • Lunch three hours after breakfast
    • One snack between lunch and dinner
    • Dinner eight hours post-glycogen-depleting protocol
    • The second snack between 10 p.m. and 11 p.m.
    • The fourth meal two to three hours before the 40km time trial on day two.
  • Prescribed recovery meals for the 24 hours post-protocol provided 8g CHO per kg body weight. All subjects received both LGI and HGI recovery diets.

 Statistical Analysis

  • ANOVA for experimental treatment x time was used to determine physiological differences between trials
  • Time trials were analyzed using paired T-tests. 
Data Collection Summary:

Timing of Measurements

  • Seven to 10 days prior to the glycogen-depleting protocol VO2max and HRmax were determined
  • On day one baseline venous blood sample was drawn and five-minute expired air sample was collected prior to the glycogen-depleting protocol
  • Heart rate was monitored every five minutes throughout the protocol
  • Venous blood sample was drawn and five-minute expired air sample was collected at the end of the protocol
  • On day two venous blood sample was drawn and five-minute expired air sample was collected prior to 40km time trial (TT)
  • A five-minute air sample was taken the last five minutes of every 20-minute period and blood was drawn in the last minute of every 20-minute period. The last air sample was taken in the last three km and the last blood sample was drawn immediately at the end of the TT.
  • Rate of perceived exertion and heart rate was recorded every 15 minutes throughout the TT.

Dependent Variables

  • TT performance time
  • Heart rate
  • Rate of perceived exertion
  • Carbohydrate and fat oxidation (as measured by expired air sample collected via standard open air spirometry)
  • Whole blood glucose
  • Free fatty acids
  • Triglycerides
  • Plasma insulin
  • Whole blood lactate
  • Respiratory exchange ratio (as measured by expired air sample collected via standard open air spirometry).

Independent Variables

Subjects were prescribed a 24-hour recovery diet that  was either:

  • LGI
  • HGI.

Control Variables

  • Water intake during exercise was matched during both TTs
  • Subjects were not aware of performance time or heart rate
  • Glycogen-depleting protocols and TTs were performed under the same conditions:
    • Time of day
    • Temperature and humidity of the lab.
Description of Actual Data Sample:
  • Initial N: 10 males.
  • Attrition (final N): 10
  • Age: 33.6±7.4 years
  • Other relevant demographics: Average VO2max was 60.5±6.0ml per kg-1 per minute-1.

Anthropometrics 

  • Height: 175.3±7.6cm
  • Weight: 74.5 ±8.2kg.

Location

Hull, United Kingdom.

 

Summary of Results:

Key Findings

  • There was no significant difference between the TTs of the LGI and HGI trials
  • There were no significant effects for trial or time and no significant trial by time interaction for heart rate
  • For RPE there was no significant main effect for trial but there was a significant main effect for time (F=17.3, P<0.001), where RPE was significantly higher at exhaustion for both trials.
  • There was no significant main effect for time or trial for carbohydrate oxidation; trial by time interaction for carbohydrate oxidation was not significant
  • There was a significant main effect for time (F=3.4, P=0.045) but not for trial for fat oxidation; there was no significant trial by time interaction for fat oxidation
  • There were no significant effects for trial or time and no significant trial by time interaction for RER
  • There were no significant effects for trial or time and no significant trial by time interaction for whole blood glucose
  • There was a significant main effect for time (F=37.0, P=0.001) but not for trial for free fatty acids; there was no significant trial by time interaction for free fatty acids
  • There were no significant effects for trial or time and no significant trial by time interaction for triglycerides
  • There were no significant effects for trial or time and no significant trial by time interaction for insulin
  • There were no significant effects for trial or time and no significant trial by time interaction for whole blood lactate.
Author Conclusion:

Although consuming a low-GI recovery diet is associated with greater resting glucose levels and a greater carbohydrate oxidation towards the end of exercise, this appears to have no further benefit to performance.

Funding Source:
Other: Not mentioned
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? ???
  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) 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? 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%.) 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? No
  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.) No
  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? 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)? Yes
  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? ???
  10.1. Were sources of funding and investigators' affiliations described? No
  10.2. Was the study free from apparent conflict of interest? ???