EAL

NAP: Recovery (2007)

Citation:

Parkin JA, Carey MF, Martin IK, Stojanovska L, Febbraio MA. Muscle glycogen storage following prolonged exercise: effect of timing of ingestion of high glycemic index food. Med Sci Sports Exerc. 1997; 29 (2): 220-224.

PubMed ID: 9044226

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 examine the effect of delaying the ingestion of high glycemic index food by two hours on muscle glycogen storage at eight and 24 hours following prolonged exhaustive exercise.

Inclusion Criteria:

Endurance-trained males.

Exclusion Criteria:

None specifically mentioned.

Description of Study Protocol:

Recruitment: Subjects volunteered
Design: Non-randomized clinical crossover trial
Blinding used: Not used
Intervention: Subjects assigned to Immediate Feeding or Delayed Feeding trials in non-random order.

Statistical Analysis

Two-way (time and treatment) ANOVA with repeated measures was used to compare data from two trials
When these analyses revealed significant differences, a Newman Kuels post-hoc test was used to locate the difference
When two-way ANOVA revealed a significant interaction, simple main effects analysis was used to locate differences.

Data Collection Summary:

Timing of Measurements

Subjects cycled on two separate occasions one week apart at a workload corresponding to 70% VO_2max for two hours, followed by four "all-out" 30-second sprints
Following exercise, subjects were fed five high-glycemic index meals over a 24-hour period, with the first three being fed at zero to four hours or two to six hours at two-hour intervals
Muscle biopsies were taken immediately after exercise and at eight and 24 hours post-exercise
Blood samples were obtained prior to and 30, 60 and 90 minutes after each meal.

Dependent Variables

Muscle biopsies from vastus lateralis were analyzed for glycogen and glucose-6-phosphate
Blood samples were analyzed for glucose and insulin.

Independent Variables

Immediate feeding: Subjects fed at 2, 4, 8 and 22 hours post-exercise
Delayed feeding: subjects fed at 4, 6, 8 and 22 hours post-exercise
Each meal matched for fat, protein, carbohydrate content and foods were all high glycemic index
Subjects arrived to lab after overnight fast, having refrained from exercise, alcohol, tobacco, and caffeine for 24 hours
Subjects completed diet and activity logs for 48 hours prior.

Description of Actual Data Sample:

Initial N: Six males
Attrition (final N): Six males
Age: Mean, 25±4 years
Ethnicity: Not mentioned.

Other Relevant Demographics

Mean weight: 73.0±9.1 kg
Mean VO_2max: 60.5±3.2.
Location: Australia.

Summary of Results:

Other Findings

No differences were observed in incremental glucose and insulin areas after each meal, muscle glycogen or glucose-6-phosphate, when meal timings were compared.

Author Conclusion:

In conclusion, these data suggest that delayed ingestion of high-glycemic index carbohydrates, by up to two hours, does not affect glycogen storage eight hours post-exercise or beyond, if the initial meal is followed by further carbohydrate intake
It is likely that the initial contraction-mediated increase in glycogen synthase activity is subsequently regulated by the intramuscular glycogen concentration.

Funding Source:

University/Hospital:

Victoria University of Technology, Royal Melbourne Institute of Technology (Australia)

Reviewer Comments:

Recruitment methods, inclusion criteria and exclusion criteria were not well-defined
The small number of subjects may have resulted in no differences.

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?	???
	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?		N/A
	3.1.	Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT)	N/A
	3.2.	Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline?	N/A
	3.3.	Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.)	N/A
	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?	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?	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?		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?		???
	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?	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?	Yes
	10.2.	Was the study free from apparent conflict of interest?	Yes