Hydration and Physical Activity
Millard-Stafford ML, Sparling PB, Rosskopf LB, Snow TK. Should carbohydrate concentration of a sports drink be less than 8% during exercise in the heat? Int J Sports Nutr Exerc Metab. 2005; 15 (2): 117-130.PubMed ID: 16089271
Randomized crossover trial
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To determine if commercially available 6% sucrose-glucose and 8% fructose-glucose-maltodextrin carbohydrate-electrolyte drinks would differentially affect physiological responses, relative fluid uptake and run performance, compared to water placebo in the heat.
- Highly-trained male distance runners
- Aged less than 40 years
- Training of 110km per week for the last three months with no anticipated change in training throughout the duration of the study
- Use of programmed drinking during training
- Completion of a 32-kilometer training run in the month before the study.
Excluded if not included above.
Description of Study Protocol:
- Recruitment: Methods not specified; all were from the Georgia Tech cross-country team
- Design: Randomized crossover trial
- Blinding used: Double-blind.
- Subjects ran 32km while ingesting a placebo, 6% or 8% carbohydrate-electrolyte solutions
- At 15km, a 250ml drink labeled with deuterium oxide was ingested
- Trial was separated by 14 days
- 400ml consumed 15 minutes before the run and 250ml was consumed every five km.
- A two-way ANOVA with repeated measures was used to determine differences between trials
- ANCOVA was utilized on run performance data to account for different heat indices on different testing days.
Data Collection Summary:
Timing of Measurements
- Heart rate, ratings of perceived exertion and core temperature were measured throughout the run
- Respiratory gases collected at five, 15, 21 and 27km
- Blood samples were obtained before exercise, at selected intervals during exercise (not mentioned) and immediately after exercise.
- Heart rate was measured using telemetry
- Core temperature was measured with a telethermometer
- RPE was measured with a Borg scale
- Respiratory gases were collected using a Douglas bag
- Blood samples were analyzed for serum glucose, electrolytes, hemoglobin, lactate, hematocrit.
Independent VariablesPlacebo, 6% or 8% carbohydrate-electrolyte solutions.
Control VariablesRunners were asked to follow a standard-normal mixed diet (55% CHO, 15% protein, 30% fat) and to duplicate training for three days prior to testing.
Description of Actual Data Sample:
- Initial N: 10 men
- Attrition (final N): 10
- Age: Mean, 23.7±3.6 years
- Ethnicity: Not mentioned
- Location: Georgia.
Summary of Results:
- Environmental conditions were not similar on all testing days
- Blood glucose and respiratory exchange ratio were significantly higher for the 6% and 8% carbohydrate-electrolyte drinks, compared to placebo (P<0.05)
- There were no significant effects of the treatments on relative change in plasma volume, plasma osmolality or serum electrolytes
- Rectal temperature at 32km was higher for the 8% compared to placebo, but similar to the 6% solution
- Deuterium oxide accumulation was not different among trials
- Run performance was 8.5% faster for the 8% carbohydrate-electrolyte solution (1,062±31 seconds, P<0.05), compared to placebo (1,154±56 seconds) and tended to be faster (7%) for the 6% carbohydrate-electrolyte solution (1,078±33 seconds). There were no differences in performance between the two carbohydrate-electrolyte solutions.
- Congruent with ACSM guidelines, we observed an 8% CHO sports drink (containing 3.3% fructose) is clearly within the range for optimal CHO content and can enhance performance during competitive distance running in the heat
- No meaningful differences were observed in the relative fluid uptake or other measures reflecting the state of hydration between 6% and 8% commercially available sports drinks during running
- Moreover, these data suggest that among acclimatized distance runners, CHO availability (vs. achieving a similar peak core temperature) limits prolonged running performance in the heat.
Authors note the possibility of Type II errors resulting from uncontrolled environmental conditions.
Quality Criteria Checklist: Primary Research
|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|
|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)||Yes|
|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?||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?||???|
|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?||Yes|
|6.5.||Were co-interventions (e.g., ancillary treatments, other therapies) described?||Yes|
|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?||???|
|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?||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|