EAL

NAP: Training (2007)

Citation:

Casey A, Short AH, Curtis S, Greenhaff PL. The effect of glycogen availability on power output and the metabolic response to repeated bouts of maximal, isokinetic exercise in man. Eur J Appl Physiol. 1996; 72: 249-255. PubMed ID: 8820894

Study Design:

Randomized controlled trial

Class:

A - Click here for explanation of classification scheme.

Quality Rating:

NEUTRAL: See Quality Criteria Checklist below.

Research Purpose:

To investigate the effect of glycogen availability on performance and metabolite accumulation during repeated bouts of maximal isokinetic cycling exercise in man.

Inclusion Criteria:

Healthy, physically active males.

Exclusion Criteria:

None specifically mentioned.

Description of Study Protocol:

Recruitment: Methods not described
Design: Randomized controlled trial
Blinding used: Not used; lab tests
Intervention: Isoenergetic low- or high-CHO diets for three days.

Statistical Analysis

Differences in total work production during each bout of maximal exercise before and after dietary manipulation were examined using repeated-measures ANOVA, using dietary condition and time as factors
Student's T-test for paired comparisons was used as a post-hoc test when significant interactions were detected within treatments
Differences in time to exhaustion were examined using an unpaired T-test
Blood metabolite data was analyzed using an unbalanced repeated-measures ANOVA, employing a first order autoregressive model.

Data Collection Summary:

Timing of Measurements

Subjects performed four bouts of 30-second maximal isokinetic cycling exercise at 100 revolutions per minute, each bout being separated by four minutes of recovery
Four days later, all subjects cycled intermittently to exhaustion at 75% VO_2max and then were assigned to isoenergetic low- or high-CHO diets for three days
On the following day, all subjects performed 30 minutes of cycling at 75% VO_2max and, after a two-hour interval, repeated the four bouts of 30-second maximal exercise
Blood samples obtained before exercise, immediately after, following two minutes of recovery and following two, five and 10 minutes of recovery from the final exercise bout.

Dependent Variables

Blood samples analyzed for lactate and ammonia concentration
Athletic performance measured through average power production.

Independent Variables

Isoenergetic high (81.5+0.4% CHO) or low (7.8±0.6% CHO) diets for three days
Prior to study, subjects recorded food intake for three days.

Description of Actual Data Sample:

Initial N: 12 healthy males
Attrition (final N): 11 males; one dropped out due to illness; six on low-CHO, five on high-CHO diet.
Age: Mean, 25±1 years
Ethnicity: Not mentioned
Other relevant demographics: Body mass, 73.4±3.2kg
Anthropometrics: Demographics of groups not compared; subjects matched on VO_2max
Location: United Kingdom.

Summary of Results:

	Total Work; Bout One	Total Work; Bout Two	Total Work; Bout Three	Total Work; Bout Four
T1; Normal-CHO	442±23	380±16	323±15	304±11
T2; Normal-CHO	449±20	372±15	319±12	304±12
T3; Low-CHO	408±31, P<0.05	340±18, P<0.05	306±16, P<0.05	300±17
T1; Normal-CHO	452±19	403±13	366±25	360±29
T2; Normal-CHO	444±9	406±17	368±24	346±27
T3; High-CHO	433±11	406±13	377±23	361±24

Other Findings

No difference was seen when comparing total work production during each bout of exercise before and after a high-CHO diet
There was no significant difference between groups in time to exhaustion
After a low-CHO diet, total work decreased from 449±20 to 408±31J per kg body mass in Bout One (9.7±3.0%, P<0.05), from 372±15 to 340±18J per kg body mass in Bout Two (8.6±2.7%, P<0.05) and from 319±12 to 306±16J per kg in Bout Three (4.5±1.7%, P<0.05), but was unchanged in Bout Four
Blood lactate and plasma ammonia accumulation during maximal exercise was lower after a low-CHO diet (P<0.001), but unchanged after a high-CHO diet.

Author Conclusion:

In summary, muscle glycogen depletion appeared to impair performance during the initial three bouts of maximal exercise, but to have no effect thereafter
The mechanism underlying this effect remains unclear
Irrespective of glycogen availability, prolonged submaximal exercise, per se, appeared to have no direct effect on subsequent maximal exercise performance.

Funding Source:

Government:

Instituto Carlos III

Reviewer Comments:

Recruitment methods, inclusion criteria and exclusion criteria were not well-defined
Groups were not compared
Power calculations were not 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?		???
	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?		???
	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?	???
	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?		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?		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?		???
	9.1.	Is there a discussion of findings?	Yes
	9.2.	Are biases and study limitations identified and discussed?	No
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