EAL

NAP: Recovery (2007)

Citation:

Abt G, Zhou S, Weatherby R. The effect of a high-carbohydrate diet on the skill performance of midfield soccer players after intermittent treadmill exercise. J Sci Med Sport. 1998; 1 (4): 203-212.

PubMed ID: 9923728

Study Design:

Randomized crossover trial

Class:

A - Click here for explanation of classification scheme.

Quality Rating:

NEUTRAL: See Quality Criteria Checklist below.

Research Purpose:

To determine whether:

Exercise of a nature, distance and intensity similar to that of soccer-match play could induce a reduction in the skill performance of midfield soccer players
Whether a high-carbohydrate diet could improve skill performance in midfield soccer players.

Inclusion Criteria:

Trained male recreational midfield soccer players
All engaged in regular training twice per week
All engaged in competition once or twice per week.

Exclusion Criteria:

Subjects underwent a medical history questionnaire and a 12-lead ECG exam to ensure no contraindications to the proposed experimental procedure.

Description of Study Protocol:

Recruitment: Subjects voluntarily participated
Design: Randomized crossover trial
Blinding used: Single-blind
Intervention: Mixed or high-carbohydrate diet for 48 hours
Statistical Analysis: Data was analyzed by repeated-measures MANOVA. When significant multivariate differences were found, univariate tests of significance were used to locate where differences lay.

Data Collection Summary:

Timing of Measurements

Subjects completed 60 minutes of intermittent treadmill exercise followed by a mixed- or high-carbohydrate diet for 48 hours
A modified Zelenka Functional Performance Test was then administered, followed by the intermittent treadmill exercise and another skills test
Subjects repeated the protocol two weeks later under the alternative dietary regimen
Blood samples were obtained pre-exercise and after each procedure
Heart rate was recorded during and after each procedure.

Dependent Variables

Blood samples were analyzed for hematocrit, hemoglobin, plasma glucose and lactate
Heart rate was measured with the Polar Sport Tester PE 4000.

Independent Variables

Mixed diet (40kcal per kg per day, 40% CHO or four grams CHO per kg per day, 30% fat, 30% protein)
High-carbohydrate diet (40kcal per kg per day, 80% CHO or eight grams CHO per kg per day, 10% fat, 10% protein)
Meals were provided to subjects and they were instructed to eat only provided foods.

Description of Actual Data Sample:

Initial N: Six males
Attrition (final N): Six
Age: Mean, 18±0.73 years
Ethnicity: Not mentioned
Other relevant demographics: Mean weight, 68.72±1.4kg; mean VO_2max, 61.97±2.0
Location: Australia.

Summary of Results:

	Pre-Intermittent Treadmill Exercise	Post-Intermittent Treadmill Exercise
Shooting Accuracy (Goals); High CHO	4.50±0.12	4.23±0.12
Shooting Accuracy (Goals); Mixed	4.07±0.31	3.93±0.37
Time to Completion (Seconds); High CHO	26.88±1.29	26.82±1.51
Time to Completion (Seconds); Mixed	27.00±1.28	25.23±1.16, P<0.05

Other Findings

The skill performance was not impaired by the intermittent treadmill exercise (P>0.05)
There was a significant decrease in the time required to complete the skill test from pre- to post-treadmill exercise for the mixed diet condition (P<0.05), amounting to a 6.55% increase in speed
The high-carbohydrate diet did not increase the ability of players to shoot or dribble (P>0.05)
A significant increase was seen in heart rate during the post-treadmill exercise skill test, compared with that during the pre-treadmill exercise test (P<0.05)
There were no significant differences in plasma glucose, plasma lactate or hemoglobin concentrations between tests (P>0.05), but MANOVA analysis detected a significant order-by-time effect for hematocrit
There was a significant decrease in body mass from pre- to post-dietary regime within both conditions (P<0.05).

Author Conclusion:

In summary, the results of the present study showed that:

The prescribed intermittent treadmill exercise did not affect the ability of the player to execute the complex game skills of shooting and dribbling
The 48-hour high-carbohydrate diet had no significant influence on skill performance.

It is speculated that either:

Muscle glycogen depletion may not impair the ability of the player to execute game skills
An alternative fatigue mechanism, such as dehydration or increased lactate production, leading to inhibition of muscle contractile processes may be causative factors in the reduction in skill performance during match-play
The treadmill protocol employed failed to induce a degree of glycogen depletion large enough to cause a significant fall in skill performance.

Funding Source:

University/Hospital:

Central Queensland University, Southern Cross University (Australia)

Reviewer Comments:

Recruitment methods were not defined
Lack of significant differences could be due to small sample size
Muscle biopsy sampling was not done; the degree of glycogen depletion can only be speculated.

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?	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?	???
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?	Yes
	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?		???
	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?	???
	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?	???
	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?		Yes
	10.1.	Were sources of funding and investigators' affiliations described?	Yes
	10.2.	Was the study free from apparent conflict of interest?	Yes