NAP: Energy Balance and Body Composition (2007)


Tarnopolsky MA, Cipriano N, Woodcroft C, Pulkkinen WJ, Robinson DC, Henderson JM, MacDougall JD. Effects of rapid weight loss and wrestling on muscle glycogen concentration. Clin J Sports Med. 1996; 6 (2): 78-84.  

PubMed ID: 8673580
Study Design:
Randomized controlled trial
A - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:
To determine whether reduced muscle glycogen stores could be repleted during the 14- to 18-hour period prior to competition and to determine whether a complete wrestling tournament significantly decreased muscle glycogen stores.
Inclusion Criteria:
  • Highly-trained male wrestlers, aged 19 to 23 years
  • All subjects were free of medical conditions that would preclude participation in the study and all had performed rapid weight loss at least three times per year with no medical complications.
Exclusion Criteria:
Excluded if not included above.
Description of Study Protocol:
  • Recruitment: Subjects volunteered for study; financial incentive of $100
  • Design: Randomized controlled trial
  • Blinding used: Not blinded.


Subjects randomly assigned to Group A or Group B (methods not described)

  • Group A: Simulated wrestling tournament, four five-minute wrestling bouts (over seven hours) following a 5% body weight loss and 17-hour repletion period
  • Group B: 5% weight loss through energy restriction (1,141kcal per day), exercise, fluid restriction and dehydration methods over 72 hours.

Statistical Analysis

  • Subject characteristics analyzed through independent T-test
  • Lactate values analyzed with one-way ANOVA with repeated measures
  • Remaining data analyzed using two-way, between-within ANOVA design with Group A vs. Group B as between variables and pre-post values as within variables
  • Location of pairwise differences from ANOVA data located using Tukey post-hoc test
  • Power analysis to detect a difference would have required 34 subjects.
Data Collection Summary:

Timing of Measurements

  • Group A had muscle glycogen measured before and after each wrestling tournament, with plasma lactate measured after each bout
  • Group B had muscle glycogen measured before and after weight loss.

Dependent Variables

  • Groups A and B: Muscle glycogen content measured through muscle biopsy taken from dominant biceps brachii 
  • Group A: Plasma lactate measured through fingertip puncture samples
  • Weighed nude on balance scale.

Independent Variables

  • Assignment to Group A (simulated wrestling tournament) or Group B (5% weight loss)
  • Four of six subjects in each group kept food records of food consumed to determine energy and carbohydrate analysis
  • Ad libitum feeding between wrestling bouts.
Description of Actual Data Sample:
  • Initial N: 12 males
  • Attrition (final N): 12; six in Group A, six in Group B.


  • Group A mean: 21.2±2.1 years
  • Group B mean: 19.3±1.8 years.


Not mentioned.

Other Relevant Demographics
  • Group A mean weight: 74.4±9.9kg
  • Group B mean weight: 65.2±7.5kg.


There were no statistically significant differences between groups regarding age, height or weight.



Summary of Results:

  Baseline Weight (kg)

Post-Weight Loss (kg)

Percentage Loss

Pre-Competition Weight (kg)

A: First weight loss 74.4±10

70.4±9.4, P<0.001

5.3±0.4 73.6±9.8

A: Second weight loss


70.6±9.5, P<0.001



B: Only weight loss


61.9±7.1, P<0.001



Other Findings

  • Group A: Wrestling tournament resulted in non-significant 13% decrease in muscle glycogen concentration, yet large increases were seen in blood lactate concentrations. All of the blood lactate concentrations after each wrestling bout were significantly greater (P<0.001) than for pre-tournament level.
  • Group B: Weight loss resulted in a 54% (P<0.018) reduction in muscle glycogen concentration.
Author Conclusion:
  • In summary, the usual weight loss procedure (approximately 5% weight loss) used by wrestlers prior to a tournament resulted in a significant depletion of intramuscular glycogen concentration, presumably due to severe energy and carbohydrate restriction as well as to exercise
  • Glycogen stores were nearly completely restored following a 17-hour ad libitum feeding period
  • A simulated wrestling tournament does not have a significant effect on overall glycogen depletion across this time period when ad libitum feeding occurs. 
Funding Source:
University/Hospital: McMaster University (Canada)
Reviewer Comments:
  • Subjects volunteered
  • Food records only kept by two-thirds of subjects
  • Group A and B weights are approximately 10kg different, though not statistically significant
  • Authors note that insignificant findings for Group A may be due to ad libitum feedings between matches, insufficient intensity in the simulated tournament, compared to an actual tournament, improper muscle sampling, type II error and the possibility that glycogen repletion occurs between bouts.
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? 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%.) 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? 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? ???
  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? ???
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? ???
  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)? 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? Yes
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