EAL

NAP: Training (2014)

Citation:

Howarth KR, Philips SM, MacDonald MJ, Richards D, Moreau NA, Gibala MJ. Effect of glycogen availability on human skeletal muscle protein turnover during exercise and recovery, J Appl Physiol. 2010; 109: 431-438.

Study Design:

Randomized Crossover Trial

Class:

A - Click here for explanation of classification scheme.

Quality Rating:

POSITIVE: See Quality Criteria Checklist below.

Research Purpose:

To examine the effect of glycogen availability on whole body and skeletal muscle protein turnover at rest, during prolonged aerobic exercise and during recovery using contemporary stable isotope tracer technology.

Inclusion Criteria:

Free of risk factors associated with CVD, pulmonary or metabolic diseases.

Exclusion Criteria:

Not available.

Description of Study Protocol:

Design

Randomized crossover trial, with two trials separated by seven days. Before each experimental trial, subjects performed a standardized bout of cycle exercise to reduce glycogen content in the vastus lateralis muscle. After the dietary intervention, subjects returned to the laboratory for the experimental trial, which involved four hours of rest, two hours of two-leg knee extensor exercise and one hour of recovery.

Intervention

The glycogen depletion protocol was followed by the ingestion of either a Low-CHO (L-CHO) or High-CHO (H-CHO) diet for 44 hours. Subjects assigned to the H-CHO diet consumed high-CHO food and subjects assigned to the L-CHO diet were given a sugar-free beverage and asked to refrain from eating for two hours. For the next 43 hours to 45 hours, subjects followed their assigned diet and were instructed to refrain from alcohol and exercise. Subjects were given lists of acceptable food choices for H-CHO or L-CHO foods along with sample diets but were allowed to consume food of their own choosing for the initial trial with no energy restrictions. For the second trial, diets were designed for the subjects in an attempt to match the energy intake of the initial trial but consuming foods from the opposite list.

Statistical Analysis

Paired T-test for muscle glycogen utilization during exercise
Two-factor repeated measures ANOVA (diet x time) for all other muscle and blood variables.

Data Collection Summary:

Timing of Measurements

All data measured during rest (pre-trial), during exercise (over the two hours) and at recovery (after one hour).

Dependent Variables

Muscle glycogen concentrations at rest, during exercise and recovery
Cardiorespiratory measures and blood flow (O₂ uptake, RER, HR, VE)
¹³CO₂ and bicarbonate retention
Whole-body leucine balance
Muscle protein turnover
Blood glucose uptake and insulin concentration.

Independent Variables

Dietary intervention post-glycogen depletion (High-CHO vs. Low-CHO diet for 43 hours to 45 hours).

Control Variables

Length of dietary intervention
Randomized crossover design
Trial timing and timing of measurements
Glycogen depletion session
Kcal intake level
Beverage intake prior to experimental trials
Exercise intensity.

Description of Actual Data Sample:

Initial N: Six males
Attrition (final N): Six
Age: 24±1 years
Other relevant demographics: Habitually active, but not specifically training for competition; VO_2peak 44±3ml per kg per minute
Anthropometrics: BM 80±5kg
Location: Hamilton, Ontario, Canada.

Summary of Results:

Key Findings

Muscle glycogen was lower in Low-CHO vs High-CHO diet group at rest, after exercise and after recovery (P<0.05)
Net leg protein balance was decreased in Low-CHO group compared with at-rest and compared with High-CHO group (due to increase in protein degradation, as well as decrease in protein synthesis late in exercise)
No changes during exercise in rate of appearance compared with at rest in High-CHO group; whole body Leu oxidation increased above rest in Low-CHO group and was higher than in the High-CHO group (P<0.05)
Whole body net protein balance was reduced in Low-CHO group (P<0.05), due to decrease in whole body protein synthesis.

Author Conclusion:

CHO availability influences rates of skeletal muscle and whole body protein synthesis, degradation and net balance during prolonged exercise in humans.

Funding Source:

Government:

Natural Sciences and Engineering Res COuncil of Canada; Canadian Institutes for Health Research

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?		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?	N/A
	2.3.	Were health, demographics, and other characteristics of subjects described?	No
	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.)	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?		N/A
	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%.)	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?		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?	Yes
	6.8.	In diagnostic study, were details of test administration and replication sufficient?	Yes
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)?	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